Anette Eleonora Gunnæs

• Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub; Grabec, Tomáš & Seiner, Hanuš [Show all 11 contributors for this article] (2026). Screening for new elastocaloric materials in a compositionally graded NiCuTiZr thin film. Materialia. 50, p. 1–16. doi: 10.1016/j.mtla.2026.102896. Full text in Research Archive Show summary

  NiTi-based shape memory alloys can be used as the active material in elastocaloric cooling devices. For optimal performance, they should simultaneously exhibit high reversibility and low temperature hysteresis, which can be achieved by ensuring that the middle eigenvalue of the primary stretch matrix λ2=1. Also, an adequate transformation temperature and a high enthalpy of transformation are required. In this study, a systematic screening for highly reversible shape memory alloys was performed, using compositionally graded Ni-Cu-Ti-Zr thin films generated by magnetron sputtering. Based on experimental data from the literature, a model predicting λ2 from the quaternary film compositions indicated a range of targeted compositions with λ2=1. The properties of the thin-film compositions were experimentally investigated to corroborate the theoretical possibilities. Martensitic phase transformations were observed with differential scanning calorimetry, demonstrating a systematic change in transformation temperatures with composition. X-ray diffraction confirmed a transition between B2 austenite and B19’ martensite structures, similar to binary NiTi compounds. The targeted compositions did not exhibit the expected temperature-driven phase transformations with low hysteresis. Tensile testing revealed superelastic behaviour, but the samples were intrinsically brittle with large hysteresis and mechanical instability. This was explained by phase separation and the formation of Ti2Ni- and Ni4Ti3-like minority phases. Despite the failure to demonstrate new shape memory alloys with high reversibility, the study suggests a path to efficient searches for new alloys with novel functional properties.

• Stanciu, Anda Elena; Fischbacher, Johann; Gusenbauer, Markus; Kovacs, Alexander; Oezelt, Harald & Graff, Joachim Seland [Show all 12 contributors for this article] (2026). Tailoring Alnico magnets through micromagnetic simulations and machine learning. JPhys Materials. 9, p. 1–21. doi: 10.1088/2515-7639/ae94b3. Full text in Research Archive Show summary

  Alnico magnets have gained renewed interest in the search for rare-earth free permanent magnets due to their high thermal stability and magnetisation. However, the limited coercivity of these shape-anisotropy-based alloys constrains their performance. Their coercivity can be improved by tailoring their structure at the micro- and nano-levels and by identifying the elemental composition and crystal structure that would increase anisotropy. Alnico alloys are composed of millimetre-to-micrometer-sized grains of different sizes and orientations. Inside each grain, magnetic nanorods embedded in a non-magnetic matrix form as a result of thermo-magnetic treatment of the cast alloy. Starting from a reference Alnico sample, we realised a finite elements micromagnetic study of exchange-decoupled rods by varying their dimensions and interrod spacing across those observed experimentally. We computed the hysteresis properties by progressing from micromagnetic simulations of a small number of rods within the magnetostatic field of their neighbours to large systems treated statistically based on the distribution of orientations of the grains. We compared the coercivity of an isolated rod with that of the exchange-decoupled system to highlight the effect of agnetostatic interactions. We computed analytically the stray field acting on a single rod as a consequence of its surrounding rods in order to confirm the scaling of the coercivity with the packing fraction p. We explored how intrinsic material properties influence magnetic behaviour by examining materials with different magnetocrystalline anisotropy constants and saturation polarisation values. Results from several hundred simulations were used to train a multi-layer perceptron regressor and predict the magnetic properties as function of the dimensions of the rods, interrod spacing and orientation of the grains. With this approach, we highlight the underlying trends by which nanoscale structuring, intrinsic material properties and grain alignment can be tailored to improve the magnetic properties of Alnico alloys.

• Larsen, Aleksander Amble; Gorantla, Sandeep; Nguyen, Phuong Dan; Rosnes, Andreas; Xu, Yijiang & Iordanidou, Konstantina [Show all 10 contributors for this article] (2026). Atomic-Resolution EDS Characterization of Ordering in a β–Cu–Zn–Al Alloy. Metallurgical and Materials Transactions A. ISSN 1073-5623. doi: 10.1007/s11661-025-08093-9. Full text in Research Archive Show summary

  Abstract Atomic ordering in single-crystal β –Cu–Zn–Al, relevant to the martensitic transformation and functional properties, is investigated using analytical STEM. Atomic-resolution EDS along the [110] zone axis, where all Wyckoff positions are spatially resolved, reveals three chemically distinct site occupancies. Correlation with HAADF-STEM contrast provides real-space evidence consistent with L2 1 ordering. In agreement with experiments, first-principles calculations show a slight energetic preference for L2 1 over D0 3 , with finite-temperature free-energy calculations indicating that this preference persists at elevated temperatures.

• Rahman, Jamil Ur; Soltani, Nayereh; Sunding, Martin Fleissner; Løvvik, Ole Martin; Gunnæs, Anette Eleonora & Finstad, Terje Gunnar [Show all 7 contributors for this article] (2026). Deciphering the structure of a high entropy Heusler antimonide. Acta Materialia. ISSN 1359-6454. Full text in Research Archive
• Karami, Mostafa; Carvalho, Patricia Almeida; Gunnæs, Anette Eleonora; Løvvik, Ole Martin & Chen, Xian (2025). Grain boundary compatibility and its impact on the reversibility of superelastic micropillars. Journal of the Mechanics and Physics of Solids. ISSN 0022-5096. 205, p. 1–12. doi: 10.1016/j.jmps.2025.106309. Full text in Research Archive Show summary

  The mechanical reversibility of stress-induced martensitic transformations is critical for the functional durability of superelastic materials, particularly at small scale. This study investigates the impact of grain boundary (GB) compatibility on the mechanical reversibility of martensitic transformations in bicrystal Cu67Al24Mn9 micropillars. By combining the geometrically nonlinear theory with high-resolution transmission electron microscopy (TEM) and nanomechanical compression experiments, we demonstrate that the crystallographic orientation and geometric coherence of GBs play a decisive role in transformation reversibility. Micropillars with GBs satisfying a necessary condition for rank-one connections between twin laminates exhibit diffuse GB morphology and recoverable transformation strains over 10,000 cycles. The findings validate recent theoretical predictions on kinematic compatibility in polycrystalline systems with non-transforming defects. The rank-one criterion underlies a design strategy for polycrystalline superelastic alloys to achieve high fatigue-resistant without altering chemical composition. The theoretical framework opens new directions for advancing microstructural design in shape memory alloys.

• Álvarez, José Luis Garrido; Lopez-Garcia, Javier; Dura, Oscar J.; Schrade, Matthias; Poulia, Anthoula & González, Carlos F. Gutiérrez [Show all 14 contributors for this article] (2025). Synergistic effects of Sb doping and nanostructuring on spark plasma-sintered ZrNiSn thermoelectrics. Materials Advances. p. 1–11. doi: 10.1039/d5ma01100k. Full text in Research Archive Show summary

  Nanostructured ZrNiSn and ZrNiSn1−xSbx (x = 0.02 and 0.05) half-Heusler alloys were successfully synthesized via mechanical milling followed by spark plasma sintering. All samples crystallized in the expected MgAgAs-type crystal structure (space group 𝐹-43m) and retained their nanostructured powder morphology post-sintering. Thermoelectric measurements revealed that the mechanical milling effectively reduced lattice thermal conductivity, while Sb doping significantly enhances the electrical conductivity in the ZrNiSn system. However, extending the milling time beyond 5 hours led to reduced performance due to the increased structural disorder without further thermal conductivity decrease. Hall effect measurements yielded a relatively low effective carrier mass of around 0.7-1.3 me, which accounts for the observed reduction in the Seebeck coefficient. The optimal Sb doping level was found to be x = 0.02. At this doping level, a substantial improvement in thermoelectric performance is detected with a maximum thermoelectric figure of merit (ZT) of approximately 0.6 at 600 K (two folds that of the undoped sample) and a 60% improvement over the unmilled ZrNiSn0.98Sb0.02 alloy These results highlight the synergistic effects of controlled Sb doping and nanostructuring via mechanical milling on optimizing the thermoelectric properties of ZrNiSn-based half-Heuslers.

• Ravuri, SyamSai; Wrobel, Pawel S.; Gorantla, Sandeep; Bazioti, Kalliopi; Sunding, Martin Fleissner & Lis, Krzysztof [Show all 11 contributors for this article] (2024). High yield and wide lateral size growth of α-Mo2C: exploring the boundaries of CVD growth of bare MXene analogues. Nanotechnology. ISSN 0957-4484. 35(15). doi: 10.1088/1361-6528/ad1c97. Full text in Research Archive Show summary

  Synthesis of Mo2C bare MXenes, without surface terminations groups, via chemical vapor deposition (CVD) on metal foils is scientifically a very intriguing crystal growth process, and there are still challenges and limited fundamental understanding to overcome to obtain high yield and wide crystal size lateral growth. Achieving large area coverage via direct growth is scientifically vital to utilize the full potential of their unique properties in different applications. In this study, we sought to expand the boundaries of the current CVD growth approach for Mo2C MXenes and gain insights into the possibilities and limitations of large area growth, with a particular focus on controlling Mo concentration. We report a facile modification of their typical CVD growth protocol and show its influence on the Mo2C synthesis, with growth times spanning up to 3 h. Specifically, prior to initiating the CVD growth process, we introduced a holding step in temperature at 1095 °C. This proved to be beneficial in increasing the Mo concentration on the liquid Cu growth surface. We achieved an average Mo2C crystals coverage of approximately 50% of the growth substrate area, increased tendency of coalescence and merging of individual flakes, and lateral flake sizes up to 170 μm wide. To gain deeper understanding into their CVD growth behavior, we conducted a systematic investigation of the effect of several factors, including (i) a holding step time on Mo diffusion rate through molten Cu, (ii) the Cu foil thickness over the Mo foil, and (iii) the CVD growth time. Phase, chemical and microstructural characterization by x-ray diffraction, x-ray photon spectroscopy, SEM and scanning/transmission electron microscopy revealed that the grown crystals are single phase α-Mo2C. Furthermore, insights gained from this study sheds light on crucial factors and inherent limitations that are essential to consider and may help guide future research progress in CVD growth of bare MXenes.

• Reiersen, Magnus; Gunnæs, Anette Eleonora; Azar, Amin S.; Diplas, Spyridon; Du, Qiang & M'Hamdi, Mohammed (2023). Accelerated material development for laser powder-bed fusion using the arc melting process. IOP Conference Series: Materials Science and Engineering. ISSN 1757-8981. 1274. doi: 10.1088/1757-899X/1274/1/012014. Full text in Research Archive Show summary

  Metal additive manufacturing has in recent years gained an increasing amount of attention, especially the subgroup of laser powder-bed fusion and aluminium alloys. However, established alloys are designed for casting and forging and often require alterations to make them eligible for the challenging processing conditions. The material selection is limited and calls for new alloys tailored specifically for additive manufacturing. In this work, an analysis suite is proposed as a tool to investigate material systems quickly and in-expensively for use in additive manufacturing. The selected material system is the Al7075 aluminium alloy, which is susceptible to cracking caused by hot tearing. To resolve this issue, it is mixed with varying quantities of silicon. The effect of silicon on solidification, grain refinement, and the resulting crack susceptibility is investigated with thermodynamical calculations considering the columnar to equiaxed transition, optical microscopy, and scanning electron microscopy after being processed by arc melting. The thermodynamical calculations of the compositions indicated a trend between the decreased columnar to equiaxed transition point at elevated temperature gradients to the silicon concentration. The experimental results reflected a similar trend by observing the reduction of the average grain size in the material system from 2470 μm2 to 323 μm2 for a composition with 0 wt.% and 10.5 wt.% silicon respectively. A composition of interest from the result was further mixed with zirconium hydride to investigate its grain refining properties on the alloy. The average grain size was reduced from 1055 μm2 to 453 μm2 by the inclusion of 0.24 wt.% zirconium. As such, this work provides a new approach to investigating a material system for use in additive manufacturing.

• Kamoutsi, Helen; Haidemenopoulos, Gregory N.; Gunnæs, Anette Eleonora & Diplas, Spyridon (2023). Microstructure and Salt Fog Corrosion of Wrought Mg-Al-Zn and Mg-RE Alloys. Materials. 16(3). doi: 10.3390/ma16031004. Full text in Research Archive Show summary

  Wrought magnesium alloys have received attention due to their potential application as lightweight materials. However, their use is limited by their poor corrosion resistance. Rare earth additions have the potential to enhance corrosion resistance. The present work included a microstructural investigation and corrosion testing of the alloy WE-43, containing Nd and Y, which was compared against the more conventional compositions of AZ31 and AZ61 alloys. All three alloys exhibited a recrystallized equiaxed structure after hot rolling with the presence of second phases—precipitates. The WE-43 alloy exhibited a better corrosion resistance than AZ31 and AZ61 under salt fog testing, indicated by the lower depth of attack and lower weight loss. The second phases in the microstructure of AZ31 and AZ61 alloys determined their corrosion resistance. The second phases in the AZ31 and AZ61 alloys (based on Al-Mg and Al-Mn phases) were nobler than the Mg matrix and catholically acted, thus sacrificing the Mg matrix. The superior corrosion resistance of WE43 was due to the incorporation of Y in the oxide/hydroxide film. In addition, the second phases in the WE43 consisted of Nd and Y and were less noble than the Mg-matrix. Thus, they acted as anodic sites protecting the Mg-matrix. The above results show the beneficial effect of rare earth additions to wrought Mg alloys towards increased corrosion resistance.

• Strandbakke, Ragnar; Wragg, David Stephen; Sørby, Magnus Helgerud; Guzik, Matylda; Gunnæs, Anette Eleonora & Szpunar, Iga [Show all 12 contributors for this article] (2022). Structural properties of mixed conductor Ba1−xGd1−yLax+yCo2O6−δ. Dalton Transactions. ISSN 1477-9226. 51(48), p. 18667–18677. doi: 10.1039/d2dt02277j. Full text in Research Archive Show summary

  Ba1−xGd1−yLax+yCo2O6−δ (BGLC) compositions with large compositional ranges of Ba, Gd, and La have been characterised with respect to phase compositions, structure, and thermal and chemical expansion. The results show a system with large compositional flexibility, enabling tuning of functional properties and thermal and chemical expansion. We show anisotropic chemical expansion and detailed refinements of emerging phases as La is substituted for Ba and Gd. The dominating phase is the double perovskite structure Pmmm, which is A-site ordered along the c-axes and with O vacancy ordering along the b-axis in the Ln-layer. Phases emerging when substituting La for Ba are orthorhombic Ba-deficient Pbnm and cubic LaCoO3-based R[3 with combining macron]c. When La is almost completely substituted for Gd, the material can be stabilised in Pmmm, or cubic Pm[3 with combining macron]m, depending on thermal and atmospheric history. We list thermal expansion coefficients for x = 0–0.3, y = 0.2.

• Bazioti, Kalliopi; Løvvik, Ole Martin; Poulia, Anthoula; Carvalho, Patricia Almeida; Azar, Amin S. & Mikheenko, Pavlo [Show all 8 contributors for this article] (2022). Probing the structural evolution and its impact on magnetic properties of FeCoNi(AlMn)x high-entropy alloy at the nanoscale. Journal of Alloys and Compounds. ISSN 0925-8388. 910, p. 1–12. doi: 10.1016/j.jallcom.2022.164724. Full text in Research Archive Show summary

  We report the first nanoscale investigation of FeCoNi(AlMn)x high-entropy alloys (HEAs) processed by laser metal deposition. The structural evolution of the alloy upon chemical composition variation (0.2 ≤ x ≤ 1.5) was investigated by combining imaging and spectroscopies in (scanning) transmission electron microscopy (S)TEM with density functional theory (DFT). A gradual change from a face-centered cubic (FCC) towards an ordered full-Heusler (L21) phase by increasing the Al and Mn contents was observed. Direct imaging and atomic-scale calculations revealed a nanoscale interplay between B2 and L21 ordered structures for x = 1.5, wherein the latter, Al and Mn occupy two different Wyckoff sites. By decreasing x, the FCC phase dominates exhibiting intense phase separation tendency, ordering phenomena, and nano-precipitation. Although not chemically discriminated, plasmon-peak splitting in low-loss electron energy loss spectra revealed the presence of two valence electron densities within the FCC phase. Lorentz TEM showed that the ordered nano-precipitates and nano-sized grains with a structure based on a tripled FCC unit cell are pinning-sites for magnetic domain walls and dislocations. All alloy compositions exhibited soft-magnetic behavior with coercivity (Hc) values< 1000 A/m. The FeCoNi(AlMn)1.5 alloy with L21/B2 nanostructure showed the highest magnetization (Ms) with relatively low Hc, attributed to the large magnetic moment of Mn and the synergistic effect of Mn-Al according to DFT, whilst ordering does not impose a negative effect. Phase separation trends within the FCC phase seem to decrease the Ms however, the overall impact on the magnetic behavior is not intense, opening up for new avenues for tuning FeCoNiAlMn properties through chemically-designed phase decomposition regimes.

• Amundsen, Monika; Pike, Nicholas; Løvvik, Ole Martin; Carvalho, Patricia Almeida & Gunnæs, Anette Eleonora (2022). New structure and insight on the phase transition within the Cu-Pd-Sn system with 25 at. % Sn. Materialia. 24, p. 1–6. doi: 10.1016/j.mtla.2022.101461. Full text in Research Archive Show summary

  The Cu-Pd-Sn material system has a (Cu, Pd) 3 Sn phase region that shows an interesting and unexplored marten- sitic phase transformation. Literature on this system is limited and the description of the phases present is incom- plete and partly contradictory. With focus on a specific Cu-rich composition in this phase region (Cu 33 Pd 42 Sn 25 ) and having employed a combination of differential scanning calorimetry, X-ray diffraction, optical microscopy and density functional theory (DFT) methods we analyze the phases involved and the phase transformation tem- peratures. The martensitic transformation was found to occur at approximately 378 K upon heating and at 328 K under cooling conditions. The crystal structure of the high temperature (HT) austenite phase was identified as face centered cubic with lattice constant 𝑎 = 6 . 2261(1) Åat 473 K. DFT simulations of plausible atomic arrange- ments indicated that the HT phase was an L2 1 ( 𝐹 𝑚 ̄3 𝑚 ) type structure. The martensitic LT phase was found to be orthorhombic with a D0 11 ( 𝑃 𝑛𝑚𝑎 ) type structure with lattice parameters a = 8.9860(3) Å, 𝑏 = 5 . 9347(2) Åand 𝑐 = 4 . 5328(2) Åat 298 K.

• Rahman, Jamil Ur; Carvalho, Patricia Almeida; Soltani, Nayereh; Schrade, Matthias; Gunnæs, Anette Eleonora & Finstad, Terje Gunnar (2022). Synthesis, microstructure, and thermoelectric properties of Sb-Based high entropy alloys. Intermetallics (Barking). ISSN 0966-9795. 143. doi: 10.1016/j.intermet.2022.107495. Full text in Research Archive Show summary

  In this paper, we explore the synthesis of new antimonide compounds based upon concepts of high entropy alloys (HEA). HEAs are usually multi-element (⪆5) alloys with near the equiatomic composition. They have been given very large attention due to their vast potential within many fields. We investigated the thermoelectric transport properties of antimony-based high entropy alloys. The observed electrical conductivity, Seebeck coefficient, and thermal conductivity were comparable to those of cutting-edge half-Heusler thermoelectric alloys. Alloys with different valence electron counts (VEC) were synthesized and correlated with measured electrical properties.

• Poulia, Anthoula; Larsen, Aleksander Amble; Graff, Joachim Seland; Diplas, Spyridon; Gunnæs, Anette Eleonora & Mikheenko, Pavlo (2022). Imaging Magnetic Domain Structure of a High Entropy Alloy: Effect of Applied Magnetic Field, 2022 IEEE 12th International Conference Nanomaterials: Applications & Properties (NAP). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781665489829. p. NMM01-1–NMM01-5. doi: 10.1109/NAP55339.2022.9934250. Full text in Research Archive Show summary

  High-Entropy Alloys (HEAs) are recently introduced materials consisting of numerous—at least five—elements in nearly equal-atomic concentrations. Studying them, previously unexplored phase fields in multidimensional phase diagrams are now being explored. The HEA concept is based on a thermodynamic balance between mixing entropy and enthalpy, which defines values of several critical parameters that determine the formation of simple or complicated phases. Physical properties, like magnetism, are of great interest for these materials, even though they have not been extensively analyzed so far. Particularly, the exploration of the magnetic domain structure and its correlation with the micro- and nano-structural features of the materials is of high scientific value. In this work, we study the influence of the magnetic history on the alteration of the magnetic domain patterns in polycrystalline FeCoNiAl0.9Mn0.9 High Entropy Alloy (HEA). For the study, we introduce a combinatorial method of Electron Backscatter Diffraction and Magnetic Force Microscopy imaging, which reveals specific magnetic domain structures in the grains of different crystallographic orientations. It is found that in the HEA polycrystal, an increase of the applied magnetic field affects the formation of magnetic domains and leads to a transition from a labyrinth-like pattern to a dotted domain configuration, which is expressed differently in the differently oriented grains.

• Larsen, Aleksander Amble; Poulia, Anthoula; Azar, Amin S.; Bazioti, Kalliopi; Carvalho, Patricia Almeida & Gunnæs, Anette Eleonora [Show all 9 contributors for this article] (2021). Identifying Magnetic Phases in Additively Manufactured High-Entropy Alloy FeCoNiAlxMnx, 2021 IEEE 10th International Conference on “Nanomaterials: Applications & Properties” (NAP – 2021). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781665439077. p. NMM03-1–NMM03-4. doi: 10.1109/NAP51885.2021.9568591. Full text in Research Archive Show summary

  High-Entropy Alloys are advanced technological materials composed of several (typically five) elements in nearly equal atomic concentration. By forming these alloys, previously unknown phase fields of multidimensional phase diagrams are explored. The large number of possible substitutions of constituent elements on crystal lattice sites justifies the dominant contribution of mixing entropy over enthalpy to the free energy reduction. This leads to the formation of phases, which otherwise could not be formed in alloys with fewer main alloying elements. Here we explore magnetic and compositional properties of a High-Entropy Alloy, namely FeCoNiAl x Mn x (0.05 ≤ x ≤ 3.08), composed of magnetic (Fe, Co, Ni) and non-magnetic elements (Al, Mn). By magnetic force microscopy of a selected area, it is observed that for intermediate to low Al and Mn contents, the alloy splits in two major crystallographic phases with different magnetic properties. Elemental maps of the same area were recorded with energy dispersive spectroscopy and scanning electron microscopy. Counterintuitively, it was found that the phase rich in non-magnetic Al has stronger magnetism than the phase rich in Fe. This work showcases possible applications of the here presented HEAs as soft magnetic materials in functional magnetic elements.

• Poulia, Anthoula; Azar, Amin S.; Schrade, M.; Graff, J.S.; Bazioti, Kalliopi & Gunnæs, Anette Eleonora [Show all 8 contributors for this article] (2021). Process–Structure–Property Relationship in FeCoNiAlxMnx Complex Concentrated Alloys Processed by Additive Manufacturing. Journal of materials engineering and performance (Print). ISSN 1059-9495. 30(9), p. 6961–6971. doi: 10.1007/s11665-021-06082-8. Full text in Research Archive Show summary

  Fourteen alloys of the FeCoNiAlxMnx system were processed by laser metal deposition (LMD). The feedstock was a weighted and proportional blend of the containing elemental powders, targeting the nominal alloy compositions. Prior to processing, the composition and particle characteristics of the feedstock were assessed. The microstructural features and crystal structures of all LMD processed materials were characterized with scanning electron microscopy/energy dispersive spectroscopy and x-ray diffraction, in both as-received and heat-treated conditions. Selected samples were investigated via scanning transmission electron microscopy and electron backscattered diffraction for further structural understanding. Hardness tests, under various indentation loads and dwelling times, were performed to assess the mechanical properties of the processed samples. The results showed a rise in hardness as Al and Mn contents increase. The variation of hardness with composition follows a reverse sigma-type curve, reflecting the microstructural evolution and grain size variations in the alloys. Based on the hardness data, we suggest a trained and validated predictive model, which can be used in alloy design for future developments.

• Ruiter, Lisa de; Gunnæs, Anette Eleonora; Dysthe, Dag Kristian & Austrheim, Håkon Olaf (2021). Quartz dissolution associated with magnesium silicate hydrate cement precipitation. Solid Earth (SE). ISSN 1869-9510. 12(2), p. 389–404. doi: 10.5194/se-12-389-2021. Full text in Research Archive
• Pop-Ghe, Patricia; Amundsen, Monika; Zamponi, Christiane; Gunnæs, Anette Eleonora & Quandt, Eckhard (2021). Direct observation of intermediate twinning in the phase transformations of ferroelectric potassium sodium niobate. Ceramics International. ISSN 0272-8842. 47(14), p. 20579–20585. doi: 10.1016/j.ceramint.2021.04.067. Full text in Research Archive
• Wachowski, Sebastian Lech; Szpunar, Iga; Sørby, Magnus Helgerud; Mielewczyk-Gryń, Aleksandra; Balaguer, Maria & Ghica, Corneliu [Show all 12 contributors for this article] (2020). Structure and water uptake in BaLnCo2O6−δ (Ln = La, Pr, Nd, Sm, Gd, Tb and Dy). Acta Materialia. ISSN 1359-6454. 199, p. 297–310. doi: 10.1016/j.actamat.2020.08.018. Full text in Research Archive Show summary

  The structure of BaLnCo2O6-δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy) was studied by the means of synchrotron radiation powder X-ray diffraction, neutron powder diffraction and Transmission Electron Microscopy (TEM), while water uptake properties were analysed with the use of thermogravimetry (TG) and water adsorption isotherms. The structure refinement revealed that the dominant phase in all compositions was orthorhombic with an ordering of the A-site cations along the c-axis and ordering of oxygen vacancies along the b-axis, which was also directly evidenced by TEM. It was shown that both unit cell volume and average Co-oxidation state at room temperature decrease linearly with decreasing Ln radius. TG water uptake experiments in humidified N2–O2 gas mixture at 300 °C revealed that among all compositions, only BaLaCo2O6-δ and BaGdCo2O6-δ exhibit significant water uptake. Surface water adsorption studies showed that the α, a normalised parameter reflecting the surface hydrophilicity, mostly independently of Ln radius was close to 0.5, which means that the surface is neither hydrophobic nor hydrophilic. The results indicated that water uptake observed at 300 °C is a bulk process, which cannot be described by standard hydration/hydrogenation reaction and it is related to the layered structure of the perovskite lattice and characteristic to La or Gd being present in the lattice.

• Kalyva, Maria Evangelou; Sunding, Martin Fleissner; Gunnæs, Anette Eleonora; Diplas, Spyridon & Redekop, Evgeniy (2020). Correlation between surface chemistry and morphology of PtCu and Pt nanoparticles during oxidation-reduction cycle. Applied Surface Science. ISSN 0169-4332. 532, p. 1–6. doi: 10.1016/j.apsusc.2020.147369. Full text in Research Archive Show summary

  Process conditions during catalytic reactions induce significant changes in surface chemistry and structure of bi- (mono) metallic nanoparticles leading to their deactivation, and this can ultimately affect the reactions long-term performance. Here PtCu and Pt model nanoparticles are prepared by microwave synthesis and characterized by X-ray diffraction (XRD). Surface chemical and morphological changes of the nanoparticles during high-temperature oxidation and reduction treatments cycle are correlated by near in situ X-ray photoelectron spectroscopy (XPS) and ex situ transmission electron microscopy (TEM) - energy-dispersive X-ray spectroscopy (EDS) studies. At 300 °C the surface atomic composition of the PtCu nanoparticles switches reversibly upon the cycle and at the same time their morphology and composition are maintained. At 400 °C, the surface atomic composition does not fully restore and, while the shape is maintained, the size and composition are not. This occurs by a mechanism of Cu leaching out from the nanoparticles. These data delineate potential operating conditions for stable PtCu nanocatalysts.

• Gutterød, Emil Sebastian; Pulumati, S.H.; Kaur, Gurpreet; Lazzarini, Andrea; Solemsli, Bjørn Garding & Gunnæs, Anette Eleonora [Show all 13 contributors for this article] (2020). Influence of Defects and H2O on the Hydrogenation of CO2 to Methanol over Pt Nanoparticles in UiO-67 Metal-Organic Framework. Journal of the American Chemical Society. ISSN 0002-7863. 142(40), p. 17105–17118. doi: 10.1021/jacs.0c07153. Full text in Research Archive Show summary

  In catalysts for CO2 hydrogenation, the interface between metal nanoparticles (NPs) and the support material is of high importance for the activity and reaction selectivity. In Pt NP-containing UiO Zr-metal–organic frameworks (MOFs), key intermediates in methanol formation are adsorbed at open Zr-sites at the Pt–MOF interface. In this study, we investigate the dynamic role of the Zr-node and the influence of H2O on the CO2 hydrogenation reaction at 170 °C, through steady state and transient isotope exchange experiments, H2O cofeed measurements, and density functional theory (DFT) calculations. The study revealed that an increased number of Zr-node defects increase the formation rates to both methanol and methane. Transient experiments linked the increase to a higher number of surface intermediates for both products. Experiments involving either dehydrated or prehydrated Zr-nodes showed higher methanol and methane formation rates over the dehydrated Zr-node. Transient experiments suggested that the difference is related to competitive adsorption between methanol and water. DFT calculations and microkinetic modeling support this conclusion and give further insight into the equilibria involved in the competitive adsorption process. The calculations revealed weaker adsorption of methanol in defective or dehydrated nodes, in agreement with the larger gas phase concentration of methanol observed experimentally. The microkinetic model shows that [Zr2(μ-O)2]4+ and [Zr2(μ–OH)(μ-O)(OH)(H2O)]4+ are the main surface species when the concentration of water is lower than the number of defect sites. Lastly, although addition of water was found to promote methanol desorption, water does not change the methanol steady state reaction rate, while it has a substantial inhibiting effect on CH4 formation. These results indicate that water can be used to increase the reaction selectivity to methanol and encourages further detailed investigations of the catalyst system.

• Poulia, Anthoula; Azar, Amin S.; Svec, Peter; Bazioti, Kalliopi; Belle, Branson & Gunnæs, Anette Eleonora [Show all 8 contributors for this article] (2020). Nanoscale Magnetic Properties of Additively Manufactured FeCoNiAlxMnx High-Entropy Alloys, 2020 IEEE 10th International Conference on “Nanomaterials: Applications & Properties” (NAP – 2020). IEEE (Institute of Electrical and Electronics Engineers). ISSN 9781728185064. p. 01NMM02-1–01NMM02-5. doi: 10.1109/NAP51477.2020.9309571. Full text in Research Archive Show summary

  Magnetic properties of High-Entropy Alloys based on the Fe-Co-Ni-Al-Mn system are reported. High-Entropy Alloys are cutting-edge technological materials containing five or more elements in relatively high concentrations (5–35 at.%) within one or several solid-state solutions. These solutions are stabilized at the nanometer scale due to the high contribution of the mixing entropy to the Gibbs free energy, which can overcome the enthalpic contribution. Two magnetic alloys are found in FeCoNiAlxMnx (1.6 at.%  x  7.8 at.%) samples processed by laser metal deposition. The magnetic techniques used to screen the materials were magneto-optical imaging and magnetic force microscopy. The former allows characterizing magnetic properties within the mm-μm scale, while the latter is efficient down to the nanometer scale. Magnetic screening confirms the importance of the nanostructure in defining magnetic properties of the alloys, and the trends in the magnetic behavior as a function of the alloy composition are revealed. The experimental results suggest that it is possible to form unique alloys, which may outperform conventional magnetic materials used in a variety of applications such as transformers, screening shields and wind power generators.

• Gunnæs, Anette Eleonora; Tofan, Raluca; Berland, Kristian; Gorantla, Sandeep Madhukar; Storaas, Thomas Aarflot & Desissa, Temesgen Debelo [Show all 12 contributors for this article] (2020). Chemical stability of Ca3Co4−xO9+δ/CaMnO3−δ p–n junction for oxide-based thermoelectric generators. RSC Advances. 10(9), p. 5026–5031. doi: 10.1039/c9ra07159h. Full text in Research Archive Show summary

  An all-oxide thermoelectric generator for high-temperature operation depends on a low electrical resistance of the direct p–n junction. Ca3Co4−xO9+δ and CaMnO3−δ exhibit p-type and n-type electronic conductivity, respectively, and the interface between these compounds is the material system investigated here. The effect of heat treatment (at 900 °C for 10 h in air) on the phase and element distribution within this p–n junction was characterized using advanced transmission electron microscopy combined with X-ray diffraction. The heat treatment resulted in counter diffusion of Ca, Mn and Co cations across the junction, and subsequent formation of a Ca3Co1+yMn1−yO6 interlayer, in addition to precipitation of Co-oxide, and accompanying diffusion and redistribution of Ca across the junction. The Co/Mn ratio in Ca3Co1+yMn1−yO6 varies and is close to 1 (y = 0) at the Ca3Co1+yMn1−yO6–CaMnO3−δ boundary. The existence of a wide homogeneity range of 0 ≤ y ≤ 1 for Ca3Co1+yMn1−yO6 is corroborated with density functional theory (DFT) calculations showing a small negative mixing energy in the whole range.

• Molino, Andrea; Holzinger, J.; Lukaszuk, Katarzyna Anna; Rojo-Gama, Daniel; Gunnæs, Anette Eleonora & Skibsted, J. [Show all 11 contributors for this article] (2019). Synthesis of ZSM-23 (MTT) zeolites with differentcrystal morphology and intergrowths: effects onthe catalytic performance in the conversion ofmethanol to hydrocarbons. Catalysis Science & Technology. ISSN 2044-4753. 9(23), p. 6782–6792. doi: 10.1039/c9cy01068h. Full text in Research Archive Show summary

  A series of zeolite ZSM-23 samples prepared with different organic structure-directing agents, gave rise to crystalline phases, which show a large variety of particle dimensions. A detailed analysis of the structure of these materials revealed the presence of different levels of stacking fault defects when using different recipes. The effect of crystal size and morphology was investigated in the methanol to hydrocarbon reaction at 400 °C, showing a predominant production of hydrocarbons in the range C3–C6+ and negligible amount of aromatics (<3%) in all cases. More importantly, we show that methanol conversion and catalytic lifetime are strongly influenced by small differences in crystal size and morphology due to a preferential crystal growth along the microchannel direction.

• Bundli, Silje; Dhak, Prasanta; Jensen, Martin; Gunnæs, Anette Eleonora; Nguyen, Phuong Dan & Fjellvåg, Helmer [Show all 7 contributors for this article] (2019). Controlled alloying of Pt-Rh nanoparticles by the polyol approach. Journal of Alloys and Compounds. ISSN 0925-8388. 779, p. 879–885. doi: 10.1016/j.jallcom.2018.11.301. Full text in Research Archive
• Oyama, Kohei; Diplas, Spyridon; M'hamdi, Mohammed; Gunnæs, Anette Eleonora & Azar, Amin S. (2019). Heat source management in wire-arc additive manufacturing process for Al-Mg and Al-Si alloys. Additive Manufacturing. ISSN 2214-8604. 26, p. 180–192. doi: 10.1016/j.addma.2019.01.007. Full text in Research Archive Show summary

  Modelling of wire-arc additive manufacturing process is an effective way for adapting the optimum parameters as well as understanding and managing the sequences of layer-by-layer deposition. Some of these parameters such as toolpath, deposition intervals and heat source power play important roles in improving the process viability and cost efficiency. In this article, we have studied Al-5Mg, Al-3Si alloys as demonstrators, from both experimental and modelling perspectives, to benchmark different deposition parameters and provided guidelines for optimising the process conditions. Physical values such as total distortion and residual stress were selected as indicators for the manufacturability of the structure. The simulations were performed by Simufact Welding software, that is outfitted with the MARC solver and the experiments were executed in a robotic cell. We have introduced a method for optimising the process parameters based on the heat source power modification and selection of unique parameters for each deposition layer. This was performed by monitoring the evolution of the molten pool size and geometry when building a wall structure. The results suggest that achieving an uninterrupted deposition process entails modification of the heat input for each layer. Thus, a simple analytical method was proposed to estimate the heat input reduction coefficient for a wall structure as a function of molten pool geometry and the height at which, a new layer is being deposited. It was also shown that a generic selection of parameters for aluminium alloys may impair the eventual quality for some of the alloys due to their inherent physical properties such as high temperature flowability.

• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Carvalho, Patricia Almeida; Berland, Kristian & Sørby, Magnus Helgerud [Show all 9 contributors for this article] (2019). Long- and short-range structures of Ti1-xHfxNi1.0/1.1Sn half-Heusler compounds and their electric transport properties. CrysteEngComm. 21, p. 3330–3342. doi: 10.1039/c9ce00046a. Full text in Research Archive
• Hjelmeland, Trude Bjørgås; Bazioti, Kalliopi; Gunnæs, Anette Eleonora; Volkov, Y & Mikheenko, Pavlo (2019). Effect of colossal magnetoresistance material La0.67Ca0.33MnO3 on superconducting properties of YBa2Cu3O7-δ thin films. Journal of Magnetism and Magnetic Materials. ISSN 0304-8853. 487. doi: 10.1016/j.jmmm.2019.165335. Full text in Research Archive Show summary

  By specific design of the sample, in which SrTiO3 substrate is fully covered by a thin layer of the colossal magnetoresistive material La0.67Ca0.33MnO3 (LCMO) and the latter is partially covered by high-temperature superconductor YBa2Cu3O7-δ (YBCO), and by using multiple current and voltage contacts, direct evidence of the strong effect of LCMO on YBCO is obtained. It is found that LCMO strongly influences not only superconducting, but also normal state of YBCO, and it is argued that this is a consequence of the spin injection from the former to the latter. The effect of the deposition conditions and crystal orientation of YBCO layer on this effect is clarified. A surprising peak in the temperature dependence of resistance seen in ex-situ ab-plane oriented sample is explained as a combination of two effects: influence of spin-polarized electrons on superconductor below its critical temperature and the interface-controlled shift of Curie temperature of LCMO to low temperatures. Considering expected use of LCMO and YBCO in composite quantum computation circuits, their combination with another advanced quantum material, graphene, is explored.

• Guzik, Matylda N.; Echevarria-Bonet, Cristina; Riktor, Marit Dalseth; Carvalho, Patricia Almeida; Gunnæs, Anette Eleonora & Sørby, Magnus Helgerud [Show all 7 contributors for this article] (2018). Half-Heusler phase formation and Ni atom distribution in M-Ni-Sn (M = Hf, Ti, Zr) systems. Acta Materialia. ISSN 1359-6454. 148, p. 216–224. doi: 10.1016/j.actamat.2018.01.019. Full text in Research Archive
• Bergum, Kristin; Riise, Heine Nygard; Gorantla, Sandeep Madhukar; Lindberg, Per; Jensen, Ingvild Julie Thue & Gunnæs, Anette Eleonora [Show all 10 contributors for this article] (2018). Improving carrier transport in Cu2O thin films by rapid thermal annealing. Journal of Physics: Condensed Matter. ISSN 0953-8984. 30(7). doi: 10.1088/1361-648X/aaa5f4. Full text in Research Archive
• Lindberg, Per Filip; Gorantla, Sandeep Madhukar; Gunnæs, Anette Eleonora; Svensson, Bengt Gunnar & Monakhov, Edouard (2017). Electronic properties and morphology of copper oxide/n-type silicon heterostructures. Journal of Physics: Condensed Matter. ISSN 0953-8984. 29(31). doi: 10.1088/1361-648X/aa77bc. Full text in Research Archive
• Jensen, Ingvild Julie Thue; Gorantla, Sandeep Madhukar; Løvvik, Ole Martin; Gan, Jiantuo; Nguyen, Phuong Dan & Monakhov, Edouard [Show all 9 contributors for this article] (2017). Interface phenomena in magnetron sputtered Cu2O/ZnO heterostructures. Journal of Physics: Condensed Matter. ISSN 0953-8984. 29(43). doi: 10.1088/1361-648X/aa8799. Full text in Research Archive Show summary

  The interface between ZnO and Cu2O has been predicted to be a good candidate for use in thin film solar cells. However, the high predicted conversion efficiency has yet to be fully realized experimentally. To explore the underlying causes of this we investigate the interface between ZnO and Cu2O in magnetron sputtered samples. Two different sample geometries were made: In the first set thin layers of ZnO were deposited on Cu2O (type A), while in the second set the order was reversed (type B). Using x-ray photoelectron spectroscopy (XPS), an intermediate CuO layer was identified regardless of the order in which the Cu2O and ZnO layers were deposited. The presence of a CuO layer was supported by transmission electron microscopy (TEM) results. Changes in the electron hole screening conditions were observed in CuO near the interface with ZnO, manifested as changes in the relative peak-to-satellite ratio and the degree of asymmetric broadness in the Cu 2p peak. The suppression of the Cu 2p satellite characteristic of CuO may cause the CuO presence to be overlooked and cause errors in determinations of valence band offsets (VBOs). For the type A samples, we compare four different approaches to XPS-based determination of VBO and find that the most reliable results are obtained when the thin CuO layer and the altered screening conditions at the interface were taken into account. The VBOs were found to range between 2.5 eV and 2.8 eV. For the B type samples a reduction of the Cu 2p-LMM Auger parameter was found as compared to bulk Cu2O, indicative of quantum confinement in the Cu2O overlayer.

• Schrade, Matthias; Berland, Kristian; Eliassen, Simen Nut Hansen; Guzik, Matylda Natalia; Echevarria-Bonet, Cristina & Sørby, Magnus Helgerud [Show all 13 contributors for this article] (2017). The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X=Hf, Zr, Ti) half-Heusler alloys. Scientific Reports. 7. doi: 10.1038/s41598-017-14013-8. Full text in Research Archive Show summary

  Thermoelectric application of half-Heusler compounds suffers from their fairly high thermal conductivities. Insight into how effective various scattering mechanisms are in reducing the thermal conductivity of fabricated XNiSn compounds (X = Hf, Zr, Ti, and mixtures thereof) is therefore crucial. Here, we show that such insight can be obtained through a concerted theory-experiment comparison of how the lattice thermal conductivity κLat(T) depends on temperature and crystallite size. Comparing theory and experiment for a range of Hf0.5Zr0.5NiSn and ZrNiSn samples reported in the literature and in the present paper revealed that grain boundary scattering plays the most important role in bringing down κLat, in particular so for unmixed compounds. Our concerted analysis approach was corroborated by a good qualitative agreement between the measured and calculated κLat of polycrystalline samples, where the experimental average crystallite size was used as an input parameter for the calculations. The calculations were based on the Boltzmann transport equation and ab initio density functional theory. Our analysis explains the significant variation of reported κLat of nominally identical XNiSn samples, and is expected to provide valuable insights into the dominant scattering mechanisms even for other materials.

• Gunnæs, Anette Eleonora; Gorantla, Sandeep Madhukar; Løvvik, Ole Martin; Gan, Jiantuo; Carvalho, Patricia & Svensson, Bengt Gunnar [Show all 10 contributors for this article] (2016). Epitaxial strain-induced growth of CuO at Cu2O/ZnO interfaces. Journal of Physical Chemistry C. ISSN 1932-7447. 120(41), p. 23552–23558. doi: 10.1021/acs.jpcc.6b07197. Full text in Research Archive Show summary

  Cu2O/ZnO has been envisaged as a potential material system for the next generation thin film solar cells. So far, the experimental efforts to obtain conversion efficiencies close to the theoretically predicted value have failed. Combining aberration-corrected (scanning) transmission electron microscopy and density functional theory modelling, we have studied the interfaces between single crystal c-axis oriented ZnO and high-quality magnetron sputtered Cu2O films. Strikingly, our study shows that the first ~5 nm of the Cu-oxide films have the structure of the monoclinic CuO phase. The CuO layer is textured with the (111), (11¯1), (¯111), (1¯1 ¯1), (¯1 ¯11), (1¯11), (¯11¯1) and (100) planes parallel to the (0001) and (000¯1) ZnO interfaces. The ionic arrangement on these planes resembles the hexagonal arrangement of the ZnO interface and epitaxy exists across the interface. A continued epitaxial growth of [111] oriented Cu2O follows resulting in epitaxial 180o rotation twins in the Cu2O layer. For the case with the (100)CuO interfacial plane we have: (111)[1¯10]Cu2O II (100)[011]CuO II (0001)[11¯20]ZnO. Because of a closer lattice matching of CuO with ZnO and Cu2O, the total strain and energy is reduced compared to a pure (111)Cu2O II (0001)ZnO interface. The existence of CuO is anticipated to be a contributing factor for the low conversion efficiencies obtained experimentally.

• Gan, Jiantuo; Gorantla, Sandeep Madhukar; Riise, Heine Nygard; Fjellvåg, Øystein Slagtern; Diplas, Spyridon & Løvvik, Ole Martin [Show all 9 contributors for this article] (2016). Structural properties of Cu2O epitaxial films grown on c-axis single crystal ZnO by magnetron sputtering. Applied Physics Letters. ISSN 0003-6951. 108:152110(15), p. 1–5. doi: 10.1063/1.4945985. Full text in Research Archive Show summary

  Epitaxial Cu2O films grown by reactive and ceramic radio frequency magnetron sputtering on single crystalline ZnO (0001) substrates are investigated. The films are grown on both O- and Zn-polar surface of the ZnO substrates. The Cu2O films exhibit a columnar growth manner apart from a ∼5 nm thick CuO interfacial layer. In comparison to the reactively sputtered Cu2O, the ceramic-sputtered films are less strained and appear to contain nanovoids. Irrespective of polarity, the Cu2O grown by reactive sputtering is observed to have (111)Cu2O||(0001)ZnO epitaxial relationship, but in the case of ceramic sputtering the films are found to show additional (110)Cu2O reflections when grown on O-polar surface. The observed CuO interfacial layer can be detrimental for the performance of Cu2O/ZnO heterojunction solar cells reported in the literature.

• Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora & Luxsacumar, Sivakanesar [Show all 9 contributors for this article] (2015). Nanostructuring of undoped ZnSb by Cryo-Milling. Journal of Electronic Materials. ISSN 0361-5235. 44(8), p. 2578–2584. doi: 10.1007/s11664-015-3708-6. Full text in Research Archive Show summary

  We report the preparation of nanosized ZnSb powder by cryo-milling. The effect of cryo-milling then hot-pressing of undoped ZnSb was investigated and compared with that of room temperature ball-milling and hot-pressing under different temperature conditions. ZnSb is a semiconductor with favorable thermoelectric properties when doped. We used undoped ZnSb to study the effect of nanostructuring on lattice thermal conductivity, and with little contribution at room temperature from electronic thermal conductivity. Grain growth was observed to occur during hot-pressing, as observed by transmission electron microscopy and x-ray diffraction. The thermal conductivity was lower for cryo-milled samples than for room-temperature ball-milled samples. The thermal conductivity also depended on hot-pressing conditions. The thermal conductivity could be varied by a factor of two by adjusting the process conditions and could be less than a third that of single-crystal ZnSb.

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• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub & Grabek, Tomas [Show all 11 contributors for this article] (2025). Phase change materials for elastocaloric cooling. Full text in Research Archive
• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhardt; Kusnir, Jakub & Grabek, Tomas [Show all 10 contributors for this article] (2025). Martensitic phase transformations in a compositionally graded thin film. doi: https:/www.icomat2025.org/wp-content/uploads/2025/09/Full_program_ICOMAT2025_10092025.pdf. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Mishra, Mochan; Diplas, Spyridon; Sartori, Sabrina & Koposov, Alexey [Show all 8 contributors for this article] (2025). In situ and operando TEM: real-time nanoscale insights into emerging materials for batteries. Full text in Research Archive
• Larsen, Aleksander Amble; Huang, Xinyue; Carvalho, Patricia A.; Gunnæs, Anette Eleonora; Løvvik, Ole Martin & Chen, Xian (2025). Size and Orientation Effects in Cu-Zn-Al Shape Memory Micropillars. Full text in Research Archive Show summary

  Introduction and objective Martensitic phase transformations in Cu-Zn-Al alloys give rise to functional behaviors such as superelasticity, the shape memory effect, and elastocaloric responses, making them attractive for various applications, including solid-state cooling. While the bulk behavior of these alloys is well-characterized, their response under small-scale mechanical loading is complex and remains an area of ongoing research. This study explores the effects of pillar size and crystallographic orientation on stress-induced martensitic transformation in Cu-Zn-Al single crystals using nanomechanical compression testing. Methods Two compositions of β-phase Cu-Zn-Al single crystals were selected for nanomechanical studies. Samples were cut and prepared with surface orientations corresponding to the (001), (011), and (111) planes of the austenitic phase, as confirmed by electron backscatter diffraction (EBSD). Micropillars with diameters ranging from 0.2 to 3 µm were fabricated using focused ion beam (FIB) milling. Mechanical uniaxial compression tests were performed at room temperature using a nanoindenter to induce martensitic transformation in the pillars. Results Micropillar compression experiments revealed a clear size effect on the martensitic phase transformation. Smaller pillars showed diminished or incomplete transformation compared to larger ones. In addition, crystal orientation significantly influenced the nature and extent of the transformation, with certain orientations exhibiting more substantial transformation strains during compression. For some orientations, no transformation was observed, indicating a strong dependence on crystallographic alignment. These observations highlight how geometric confinement and crystal orientation affect martensitic phase transformation behavior in Cu-Zn-Al.

• Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Mishra, Mochan & Sunding, Martin Fleissner [Show all 11 contributors for this article] (2024). Operando and in situ transmission electron microscopy: exploring real-time nanoscale phenomena of battery materials. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Sunding, Martin Fleissner & Sartori, Sabrina [Show all 9 contributors for this article] (2024). In situ and operando (S)TEM investigations of MXene-based anodes for Li-ion all-solid-state batteries. Full text in Research Archive
• Holmestad, Randi; Gunnæs, Anette Eleonora; Nord, Magnus; Hage, Fredrik Sydow; Hansen, Vidar Folke & Prytz, Øystein [Show all 7 contributors for this article] (2024). Electron diffraction in physical science in Norway – past, present, and future. Full text in Research Archive
• Rahman, Jamil Ur; Gunnæs, Anette Eleonora; Finstad, Terje Gunnar; Løvvik, Ole Martin & Carvalho, Patricia Almeida (2023). Structure of a high entropy Heusler antimonide. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Sunding, Martin Fleissner & Sartori, Sabrina [Show all 9 contributors for this article] (2023). In situ and operando transmission electron microscopy investigations of MXene-based anodes for Li-ion all-solid-state batteries. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Ravuri, SyamSai; Wrobel, Pawel S.; Sunding, Martin Fleissner & Sartori, Sabrina [Show all 9 contributors for this article] (2023). In situ and operando transmission electron microscopy: real-time nanoscale insights into emerging materials for batteries. Full text in Research Archive
• Rahman, Jamil Ur; Sunding, Martin Fleissner; Løvvik, Ole Martin; Gunnæs, Anette Eleonora; Finstad, Terje Gunnar & Carvalho, Patricia Almeida (2023). Deciphering the structure of a high-entropy Heusler antimonide. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja [Show all 7 contributors for this article] (2023). In situ and Operando Transmission Electron Microscopy investigations of novel 2D-based anodes for Li-ion all-solid-state batteries. Full text in Research Archive
• Poulia, Anthoula; Larsen, Aleksander; Graff, Joachim Seland; Diplas, Spyridon; Gunnæs, Anette Eleonora & Mikheenko, Pavlo (2022). Imaging Magnetic Domain Structure of a High Entropy Alloy: Effect of Applied Magnetic Field. Full text in Research Archive Show summary

  High-Entropy Alloys (HEAs) are recently introduced materials consisting of numerous—at least five—elements in nearly equal-atomic concentrations. Studying them, previously unexplored phase fields in multidimensional phase diagrams are now being explored. The HEA concept is based on a thermodynamic balance between mixing entropy and enthalpy, which defines values of several critical parameters that determine the formation of simple or complicated phases. Physical properties, like magnetism, are of great interest for these materials, even though they have not been extensively analyzed so far. Particularly, the exploration of the magnetic domain structure and its correlation with the micro- and nano-structural features of the materials is of high scientific value. In this work, we study the influence of the magnetic history on the alteration of the magnetic domain patterns in polycrystalline FeCoNiAl0.9Mn0.9 High Entropy Alloy (HEA). For the study, we introduce a combinatorial method of Electron Backscatter Diffraction and Magnetic Force Microscopy imaging, which reveals specific magnetic domain structures in the grains of different crystallographic orientations. It is found that in the HEA polycrystal, an increase of the applied magnetic field affects the formation of magnetic domains and leads to a transition from a labyrinth-like pattern to a dotted domain configuration, which is expressed differently in the differently oriented grains.

• Reiersen, Magnus; Gunnæs, Anette Eleonora; Azar, Amin S.; Diplas, Spyridon; Du, Qiang & M`hamdi, Mohammed (2022). Accelerated material development for laser powder-bed fusion using the arc melting process. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja [Show all 7 contributors for this article] (2022). Novel 2D-based anodes for Li-ion all-solid-state batteries. Full text in Research Archive
• Bazioti, Kalliopi; Gorantla, Sandeep; Sunding, Martin Fleissner; Sartori, Sabrina; Diplas, Spyridon & Bachmatiuk, Alicja [Show all 7 contributors for this article] (2022). In situ and Operando Transmission Electron Microscopy investigations of MXenes for Li-ion all-solid-state batteries. Full text in Research Archive
• Løvvik, Ole Martin; Carvalho, Patricia A.; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Rajput, Kalpna & Larsen, Aleksander Amble [Show all 9 contributors for this article] (2022). Elastocaloric cooling with TiNiCuZr alloys? Full text in Research Archive
• Løvvik, Ole Martin; Rahman, Jamil Ur; Finstad, Terje Gunnar; Gunnæs, Anette Eleonora & Carvalho, Patricia Almeida (2022). Thermoelectric properties of multiple component (high entropy) silicides and antimonides. Full text in Research Archive
• Carvalho, Patricia Almeida; Rahman, Jamil Ur; Soltani, Nayereh; Schrade, Matthias; Stange, Marit Synnøve Sæverud & Gunnæs, Anette Eleonora [Show all 8 contributors for this article] (2021). Functional high entropy antimonides and silicides. Full text in Research Archive
• Carvalho, Patricia Almeida; Mayandi, Jeyanthinath; Rahman, Jamil Ur; Soltani, Nayereh; Schrade, Matthias & Gunnæs, Anette Eleonora [Show all 9 contributors for this article] (2021). Exploring the structure of high entropy oxides, silicides and antimonides for functional applications. Full text in Research Archive
• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Azar, Amin S.; Mikheenko, Pavlo & Diplas, Spyridon [Show all 7 contributors for this article] (2021). Advanced Scanning Transmission Electron Microscopy investigations of FeCoNi(AlMn)x high-entropy alloy: nanoscale structure and impact on magnetic properties. Full text in Research Archive
• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Carvalho, Patricia Almeida; Azar, Amin S. & Mikheenko, Pavlo [Show all 8 contributors for this article] (2021). STEM-EELS investigations and Lorentz microscopy unravelling the structural evolution of FeCoNi(AlMn)x high-entropy alloy and its impact on magnetic properties. Full text in Research Archive
• Larsen, Aleksander; Poulia, Anthoula; Azar, Amin S.; Bazioti, Kalliopi; Carvalho, Patricia Almeida & Gunnæs, Anette Eleonora [Show all 9 contributors for this article] (2021). Identifying Magnetic Phases in Additively Manufactured High-Entropy Alloy FeCoNiAlxMnx. Full text in Research Archive
• Poulia, Anthoula; Azar, Amin S.; Gunnæs, Anette Eleonora; Bazioti, Kalliopi; Mikheenko, Pavlo & Diplas, Spyridon (2021). Tailoring mechanical and magnetic properties of the FeCoNi(AlMn)x high entropy alloys via compositional alterations. Full text in Research Archive
• Poulia, Anthoula; Azar, Amin S.; Bazioti, Kalliopi; Gunnæs, Anette Eleonora; Mikheenko, Pavlo & Diplas, Spyridon (2021). Additively manufactured FeCoNi(AlMn)x high entropy alloys: Mechanical and magnetic properties investigation. Full text in Research Archive
• Poulia, Anthoula; Azar, Amin S.; Bazioti, Kalliopi; Gunnæs, Anette Eleonora; Mikheenko, Pavlo & Diplas, Spyridon (2021). Investigation of High Entropy Alloys via Magnetic Force Microscopy. Full text in Research Archive
• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Azar, Amin S.; Mikheenko, Pavlo & Diplas, Spyridon [Show all 7 contributors for this article] (2021). Structural evolution of FeCoNi(AlMn)x high-entropy alloy and impact on magnetic properties: nano-scale STEM-EELS investigations. Full text in Research Archive
• Pop-Ghe, Patricia; Amundsen, Monika; Zamponi, Christiane; Gunnæs, Anette Eleonora & Quandt, Eckhard (2021). Direct observation of intermediate twinning in the phase transformations of ferroelectric potassium sodium niobate. Full text in Research Archive
• Poulia, Anthoula; Azar, Amin S.; Svec, Peter; Bazioti, Kalliopi; Belle, Branson & Gunnæs, Anette Eleonora [Show all 8 contributors for this article] (2020). Nanoscale Magnetic Properties of Additively Manufactured FeCoNiAlxMnx High-Entropy Alloys. Full text in Research Archive Show summary

  Magnetic properties of High-Entropy Alloys based on the Fe-Co-Ni-Al-Mn system are reported. High-Entropy Alloys are cutting-edge technological materials containing five or more elements in relatively high concentrations (5–35 at.%) within one or several solid-state solutions. These solutions are stabilized at the nanometer scale due to the high contribution of the mixing entropy to the Gibbs free energy, which can overcome the enthalpic contribution. Two magnetic alloys are found in FeCoNiAlxMnx (1.6 at.%  x  7.8 at.%) samples processed by laser metal deposition. The magnetic techniques used to screen the materials were magneto-optical imaging and magnetic force microscopy. The former allows characterizing magnetic properties within the mm-μm scale, while the latter is efficient down to the nanometer scale. Magnetic screening confirms the importance of the nanostructure in defining magnetic properties of the alloys, and the trends in the magnetic behavior as a function of the alloy composition are revealed. The experimental results suggest that it is possible to form unique alloys, which may outperform conventional magnetic materials used in a variety of applications such as transformers, screening shields and wind power generators.

• Løberg, Monika; Pike, Nicholas; Carvalho, Patricia Almeida; Karlsen, Ole Bjørn; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2019). Martensitic-like phase transformations within the Cu-Pd-Sn system. Full text in Research Archive
• Løberg, Monika; Løvvik, Ole Martin; Carvalho, Patricia Almeida; Karlsen, Ole Bjørn & Gunnæs, Anette Eleonora (2019). Phase Transformations within the Cu-Pd-Sn system. Full text in Research Archive
• Løberg, Monika; Karlsen, Ole Bjørn; Løvvik, Ole Martin; Carvalho, Patricia Almeida & Gunnæs, Anette Eleonora (2019). Characterization of phase transformations within the Cu-Pd-Sn system - a possible shape memory alloy for energy conversion. Full text in Research Archive
• Sunding, Martin Fleissner; Løberg, Monika; Azar, Amin S.; Stange, Marit Synnøve Sæverud; Carvalho, Patricia Almeida & Karlsen, Ole Bjørn [Show all 10 contributors for this article] (2019). The Need for a Multi-Technique Approach in the Search for New Phase-Transforming Materials. Full text in Research Archive Show summary

  Introduction/Purpose Reversible diffusionless first-order phase transformations are a fundamental part of phase change materials and shape memory alloys [1]. Some of these materials even possess useful physical characteristics that show abrupt changes e.g. in their electrical[2] and magnetic [3] polarizations. These phase transformations can be studied using multiple techniques, enabling access to different types of information including length scales and time periods, but how should this characterisation be approached? Methods TEM studies give highly relevant data in this field of research, from detailed crystallographic structures, to relative orientations between grains and phases and to the phase transformation temperature. However, TEM analyses are time consuming and requires small sample sizes and ad hoc preparation. High-throughput measurement techniques are thus required in the search for improved compositions and new materials in order to rapidly assess the properties of many samples or samples with graded composition [4]. Optical methods (for example unpolarised and polarised microscopy and thermal imaging) and electric conductivity measurements can for example be used to map phase transformation temperatures much faster and on much larger areas than traditional TEM techniques. XRD and SEM-EDS-EBSD can then be applied to obtain initial crystallographic and microstructure information on an intermediate size scale, before TEM is applied for the in-depth study of the most relevant compositions. Results We applied this multi-pronged approach in the search for Heusler and half-Heusler alloys with a low temperature martensitic phase transformation and with low thermal hysteresis, with potential applications in waste heat energy harvesting. Conclusions Drawing advantage of the strengths of multiple analysis techniques – with respect to the obtainable information, the sample size and/or the time frame of the analyses – renders the search for new phase change materials more effective. It enables faster identification of potential target compositions and of sample areas optimal for in depth studies. Selected references [1] David Dye, Nature Materials14 (8), 760 (2015). [2] M. M. Vopson, Critical Reviews in Solid State and Materials Sciences40 (4), 223 (2015). [3] L. Huang, D. Y. Cong, L. Ma, Z. H. Nie, Z. L. Wang, H. L. Suo, Y. Ren, and Y. D. Wang, Applied Physics Letters108 (3) (2016). [4] M. L. Green, C. L. Choi, J. R. Hattrick-Simpers, A. M. Joshi, I. Takeuchi, S. C. Barron, E. Campo, T. Chiang, S. Empedocles, J. M. Gregoire, A. G. Kusne, J. Martin, A. Mehta, K. Persson, Z. Trautt, J. Van Duren, and A. Zakutayev, Applied Physics Reviews 4 (1), 011105 (2017).

• Strandbakke, Ragnar; Bjørheim, Tor Svendsen; Sørby, Magnus Helgerud; Wachowski, Sebastian Lech; Mielewczyk-Gryn, Aleksandra & Balaguer, Maria [Show all 9 contributors for this article] (2019). Hydration and hydrogenation of mixed conducting BaGd1‑xLaxCo2O6‑δ (BGLC). Full text in Research Archive
• Kalyva, Maria Evangelou; Redekop, Evgeniy; Johansson, Niclas; Urpelainen, Samuli; Gunnæs, Anette Eleonora & Diplas, Spyridon [Show all 7 contributors for this article] (2019). AP-XPS study of bimetallic PtCu nanoparticles supported on SiO2 films. Full text in Research Archive
• Løberg, Monika; Pike, Nicholas; Karlsen, Ole Bjørn; Carvalho, Patricia Almeida; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2019). Characterization of phase transforming, Heusler based (Cu-Pd-Sn), alloys for energy harvesting. Full text in Research Archive
• Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2018). Energy Conversion using Phase Transforming Materials - the Cu-Pd-Sn system. Full text in Research Archive
• Løberg, Monika; Løvvik, Ole Martin & Gunnæs, Anette Eleonora (2018). Martensitic like phase transformations in the Cu-Pd-Sn system. Full text in Research Archive
• Strandbakke, Ragnar; Gunnæs, Anette Eleonora; Carvalho, Patricia A.; Mielewczyk-Gryn, Aleksandra; Wachowski, Sebastian & Balaguer, Maria [Show all 8 contributors for this article] (2018). Coupled hydration, cation reorganization and red-ox in MIEC perovskites. Full text in Research Archive
• Ruiter, Lisa de; Austrheim, Håkon Olaf; Gunnæs, Anette Eleonora & Dysthe, Dag Kristian (2018). Quartz dissolution and M-S-H cement precipitation in a high pH ultramafic system. Full text in Research Archive
• Ruiter, Lisa de; Austrheim, Håkon Olaf; Dysthe, Dag Kristian & Gunnæs, Anette Eleonora (2018). Quartz weathering associated with magnesium silicate hydrate cement precipitation. Full text in Research Archive
• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Berland, Kristian; Gunnæs, Anette Eleonora & Persson, Clas [Show all 8 contributors for this article] (2017). Structural Investigation of Ti1-xHfxNiySn Half-Heusler Compounds. Full text in Research Archive
• Berland, Kristian; Eliassen, Simen Nut Hansen; Schrade, Matthias; Tofan, Raluca; Guzik, Matylda Natalia & Gunnæs, Anette Eleonora [Show all 11 contributors for this article] (2017). Using theory to understand thermoelectric materials. Full text in Research Archive
• Gunnæs, Anette Eleonora (2017). Evaluation of a thermoelectric p-n junction at the macro and nano scale by X-ray and electron probe techniques. Full text in Research Archive
• Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Gunnæs, Anette Eleonora & Ulyashin, Alexander (2017). On the evolution of properties of ITO layers deposited on crystalline and amorphous Si upon heat treatments. Full text in Research Archive
• Kepaptsoglou, Despoina Maria; Diplas, Spyridon; Ramasse, Quentin; Gunnæs, Anette Eleonora & Ulyashin, Alexander (2017). A high resolution electron microscopy and spectroscopy study of interfaces in Si-based solar cell heterojunctions. Full text in Research Archive
• Gunnæs, Anette Eleonora; Diplas, Spyros & Ulyashin, Alexander G. (2017). A TEM and XPS study of epitaxially grown amorphous hydrogenated silicon in solar cell structures. Full text in Research Archive
• Granerød, Cecilie Skjold; Nguyen, Phuong Dan; Gunnæs, Anette Eleonora & Prytz, Øystein (2016). The Structure Physics group. Full text in Research Archive
• Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian [Show all 10 contributors for this article] (2016). The effect of spark plasma sintering on structure and phase stability in half-Heusler thermoelectric alloys. Full text in Research Archive
• Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian [Show all 10 contributors for this article] (2016). Microstructural characterization of spark plasma sintered (X,X’)NiSn half‐Heusler alloys. Full text in Research Archive
• Gunnæs, Anette Eleonora (2016). Nanoscience with TEM at the Center for Material Science and Nanotechnology/NORTEM, Oslo, Norway. Full text in Research Archive
• Schrade, Matthias; Echevarria-Bonet, Cristina; Eliassen, Simen Nut Hansen; Berland, Kristian; Persson, Clas & Tofan, Raluca [Show all 9 contributors for this article] (2016). Thermal Properties of XNiSn(X = Hf, Zr, Ti) half Heusler Alloys. Full text in Research Archive
• Schrade, Matthias; Echevarria-Bonet, Cristina; Guzik, Matylda Natalia; Tofan, Raluca; Gunnæs, Anette Eleonora & Eliassen, Simen Nut Hansen [Show all 10 contributors for this article] (2016). Thermal properties of XNiSN (X = Ti, Zr, Hf) half Heusler alloys. Full text in Research Archive
• Lervik, Adrian; Bjørheim, Tor Svendsen; Nguyen, Phuong Dan; Diplas, Spyridon; Haugsrud, Reidar & Gunnæs, Anette Eleonora (2016). Chemical and Structural Investigations of Grain Boundaries in Y-Doped BaZrO3. Full text in Research Archive
• Lervik, Adrian; Haugsrud, Reidar; Diplas, Spyridon & Gunnæs, Anette Eleonora (2015). A TEM approach to BZY. Full text in Research Archive
• Gunnæs, Anette Eleonora (2015). Atomkikking med Norges supermikroskop. Full text in Research Archive
• Fjellvåg, Øystein Slagtern; Sjåstad, Anja Olafsen; Haugsrud, Reidar & Gunnæs, Anette Eleonora (2015). Investigation of Novel Hydride Oxides for Holistic Understanding of Functional Materials. Full text in Research Archive
• Song, Xin; Valset, Kjetil; Graff, Joachim Seland; Thøgersen, Annett; Gunnæs, Anette Eleonora & Carbalho, Partricia [Show all 10 contributors for this article] (2015). Nano Improves Thermoelectric Performance. Full text in Research Archive Show summary

  The rule of thumb for improving the performance of thermoelectric materials is to reduce the thermal conduction, which attributes to electron transport and phonon transport. Phonons are characterized by different wavelength, Short wavelength phonons are scattered by impurity atoms in alloyed matels, Mid- and Long wavelength phonns are scattered by the iuinterfaces. Nanostructuring can engineer the phonon transport by introduce numerous grain boundaries, thus increasing phonon scattering, further improving thermal resistance. The aim of the present study is the nano-grains of the thermoelectric material ZnSb and the correlation with thermal transport measurements. We explored cryomilling (by ball-milling powders at Cryogenic temperature) as a technique to created nano—powders of ZnSb for pressing into pellets. The effect of cryomilling flowed by hot-pressing of undoped ZnSb was investigated.

• Larsen, Aleksander Amble & Gunnæs, Anette Eleonora (2021). A Correlated Study of FeNiCoMnxAlx - Magnetic, structural, and compositional properties of additive manufactured high-entropy alloy. Universitetet i Oslo. Full text in Research Archive
• Røsvik, Mari Mathillas; Gunnæs, Anette Eleonora; Carvalho, Patricia Almeida & Schrade, Matthias (2021). Structural Characterization of High Entropy Metal Silicide Alloys An investigation of the Si:Cr:Fe:Co:Ni:Cu system. Universitetet i Oslo. Full text in Research Archive
• Solemsli, Bjørn Gading; Olsbye, Unni; Gunnæs, Anette Eleonora & Gutterød, Emil Sebastian (2020). A Study of Catalytic Pt Nanoparticles inside a Nano-porous Functionalized UiO MOF-matrix for CO2-Hydrogenation. Universitetet i Oslo. Full text in Research Archive
• Fjellvåg, Øystein; Sjåstad, Anja Olafsen & Gunnæs, Anette Eleonora (2019). Oxyhydrides – Synthesis, Crystal Structure and Properties. Universitetet i Oslo. Full text in Research Archive Show summary

  This thesis focus on the research of the new and scarcely explored material class oxyhydrides, where the anionic lattice consists of both oxide and hydride anions. Selected oxyhydrides described by the formula La2‑xNdxLiHO3 (0 ≤ x ≤ 2) have been obtained by a halide salt flux method in large quantities (gram scale). We describe key factors for preparation of oxyhydrides by this approach, and we discover lithium chloride to serve as an excellent flux also below its melting temperature, opening for a completely new temperature range for synthesis of oxyhydrides. Phase pure Nd2LiHO3 was in this work produced phase pure for the first time. Neutron diffraction was employed to study the long range and local structure of La2LiHO3, and neutron spectroscopy combined with computational methods yields new insight the migration of hydride anions in the compound based on evaluation of the chemical bonding. LaSr3Fe3O9 is found to be a new layered compound with a G-type antiferromagnetic structure which is immiscible with LaSr3Fe3O10‑δ. Preliminary neutron diffraction experiments on corresponding oxyhydrides prepared by topotactic anion-exchange with CaH2, indicate successful preparation of an oxyhydride with the composition LaSr3Fe3H1.1O8.9.

• Løberg, Monika & Gunnæs, Anette Eleonora (2017). Influence of Mn Stoichiometry on the Structure and Thermoelectric Properties of CaMn(1+y)O(3-d). Universitetet i Oslo. Full text in Research Archive Show summary

  The energy consumption of present day society is ever increasing and the sources for more and cleaner energy is sought for. A possible contributor are thermoelectric generators, which convert parts of a heat flux directly into electrical energy. Unfortunately, the efficiency of current generators is too low for large scale commercialization, and new and better materials must be designed. In the present master project, the performance of n-type thermoelectric oxide CaMn(1+y)O(3-d) is attempted improved by creating precipitates within the nano-range. The precipitates could be anticipated to enhance phonon scattering, thereby lowering thermal conductivity and enhance the overall thermoelectric properties of the material. A sample series of CaMn(1+y)O(3-d), with composition y = 0, 0.020 , 0.036, 0.074 and 0.10, has been synthesized by solid state reaction and the microstructure and thermoelectric properties were characterized. Secondary phase, CaMn2O4, precipitates were found from X-ray diffraction and Scanning Electron Microscopy in the size range 5-10 um. Further investigations into the presence of nanoprecipitates were performed by Transmission Electron Microscopy finding no areas enriched in manganese within the CaMnO3 matrix. Electrical resistivity and Seebeck coefficient were measured from room temperature up to 600C finding a resistivity ranging from 20 - 100 mOhm cm and Seebeck coefficient from -300 to -200 uVK-1, showing no trend with manganese content. Thermal conductivity measurements were performed, showing a thermal conductivity between 2.3 - 3.6 Wm-1K-1, however no trend with varying manganese content was observed. Further, the obtained thermoelectric data was compared with samples fabricated using a different synthesis method, yielding similar results and no significant variations was observed. The absence of a Mn-dependency in all transport parameters was carefully confirmed by a thorough investigation of potential experimental influences, like sample porosity, impurity level and measurement uncertainty. Finally, the results are qualitatively rationalized using a simple Callaway model for the thermal conductivity. The concluding remarks are that all manganese excess will manifest as secondary phase CaMn2O4 and no manganese rich precipitates will exist within the CaMnO3 matrix. The variation in manganese content does not influence the thermoelectric properties of CaMn(1+y)O(3-d).

• Lervik, Adrian; Haugsrud, Reidar; Diplas, Spyridon & Gunnæs, Anette Eleonora (2016). Structural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3. Universitetet i Oslo. Full text in Research Archive Show summary

  Proton-conducting electrolytes are candidates for a range of electrochemical applications. The search for one which may operate in the intermediate temperature range of 400-800 °C has been ongoing for a while, and Yttrium-doped BaZrO3 (BZY) have been established as one of the most promising materials. Unfortunately, its highly refractory nature makes processing difficult, and generally results in a small grained polycrystalline material with high areas of highly resistive grain boundaries. The cause of resistive grain boundaries is attributed to the formation of space-charge layers, where negatively charged defects segregate close to the grain boundaries in order to compensate the positively charged grain boundary core. A sample prepared unconventionally using extreme temperatures of 2200 °C overcame the grain boundary problem, but an unanswered question is: what did occur during the high temperature treatment? In this thesis, conventional samples were prepared by the Solid State Reaction (SSR) method and characterised by a range of methods. X-Ray Diffraction (XRD) indicates the presence of two cubic phases with slightly different lattice parameters, and X-ray Photoelectron Spectorscopy (XPS) shows Y situated two different chemical states with a seperation of ~2.6 eV. Energy Dispersive Spectroscopy (EDS) performed in the Transmission Electron Microscope (TEM) shows an enrichment of Y and depletion of Ba at the grain boundaries. These are strong indications that Y also substitutes on Ba site in the structure. The microstructure has grains of ~600 nm and the grain boundaries mostly adapt random configurations. Conductivity measurements by impedance spectroscopy indicates the presence of highly resistive grain boundaries, as the conductivity of grain boundaries is three orders of magnitude lower than that of bulk (0.001 vs. 0.000001 S/cm at 400 °C in wet O2). In the high temperature sample the same degree of Ba depletion is not observed, but Y also segregates to the grain boundaries. The grain boundaries are also more frequently near a Coincident Site Lattice (CSL) type grain boundary; an indication of grain boundary migration during the high temperature treatment. Furthermore, two samples prepared through the Solid State Reactive Sintering (SSRS) method, with Ba non-stoichiometry (x = ±0.02, in Ba_{x}Y_{0.15}Zr_{0.75}O_{3}), have been studied by TEM. The goal was to gain more understanding on how the addition of small amounts of NiO assists in the sintering stage, and how it is distributed in the resulting sample. The results shows that Ni rich phase(s) are present at the grain boundaries and triple points in the Ba rich sample. In the Ba deficient sample no secondary phases are observed, but the Ni content is found to be twice as high at the grain boundaries than in the grain interior (bulk).

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