Ole Martin Løvvik

• Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub; Grabec, Tomáš & Seiner, Hanuš [Vis alle 11 forfattere av denne artikkelen] (2026). Screening for new elastocaloric materials in a compositionally graded NiCuTiZr thin film. Materialia. 50, s. 1–16. doi: 10.1016/j.mtla.2026.102896. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Grimenes, Øven Andreas; Løvvik, Ole M. & Berland, Kristian (2026). Exceptional thermoelectric properties in Na2TlSb enabled by quasi-one-dimensional band structure. Physical review B (PRB). ISSN 2469-9950. 113(15). doi: 10.1103/jnfj-2n8p. Fulltekst i vitenarkiv Vis sammendrag

  Materials with reduced dimensionality offer beneficial density-of-states (DOS) profiles for thermoelectric energy conversion, but can be impractical in realistic devices. Encouragingly, bulk high-symmetry materials can also exhibit similar quasi-low-dimensional band structures. A striking example is the full-Heusler compound Na2⁢TlSb, whose valence-band energy isosurfaces can form intersecting two-dimensional pockets, i.e., a boxlike structure. The individual energy isosurface sheets resemble those of 1D quantum wires. The combination of high electron velocities (perpendicular to the pockets) and a rapidly increasing DOS with energy in the transport regime (due to the low dimensionality) makes Na2⁢TlSb a representative case where the band structure gives rise to attractive electronic transport properties. However, these beneficial features could be counteracted by high electronic scattering rates due to the large scattering space. In this first-principles study of Na2⁢TlSb, we find that the electronic scattering rates remain modest. This result is linked to the reduced matrix elements of large-momentum (𝐪) scattering across the delocalized energy isosurfaces. The enhanced free-carrier screening due to the large DOS also contributes to reducing scattering. In combination, the low-dimensional features and modest scattering result in excellent electronic transport properties. Combined with an ultralow lattice thermal conductivity of 𝜅ℓ<1W/mK reported in the literature, we predict a thermoelectric figure of merit ranging from 2.4 at 300 K to 4.4 at 600 K. The 𝑛-type properties are also favorable, with 𝑧⁢𝑇 values from 1.5 at 300 K to 3.0 at 600 K.

• Larsen, Aleksander Amble; Gorantla, Sandeep; Nguyen, Phuong Dan; Rosnes, Andreas; Xu, Yijiang & Iordanidou, Konstantina [Vis alle 10 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 7 forfattere av denne artikkelen] (2026). Deciphering the structure of a high entropy Heusler antimonide. Acta Materialia. ISSN 1359-6454. Fulltekst i vitenarkiv
• 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, s. 1–12. doi: 10.1016/j.jmps.2025.106309. Fulltekst i vitenarkiv Vis sammendrag

  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 [Vis alle 14 forfattere av denne artikkelen] (2025). Synergistic effects of Sb doping and nanostructuring on spark plasma-sintered ZrNiSn thermoelectrics. Materials Advances. s. 1–11. doi: 10.1039/d5ma01100k. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Grimnes, Øven Andreas; Snyder, G. Jeffrey; Løvvik, Ole Martin & Berland, Kristian (2025). Thermoelectric transport of strained CsK2 Sb: Role of electron velocities and scattering within extended Fermi surfaces. Physical review B (PRB). ISSN 2469-9950. 111(19), s. 1–12. doi: 10.1103/PhysRevB.111.195205. Fulltekst i vitenarkiv Vis sammendrag

  In this first-principles study, we investigated the thermoelectric properties of the full-Heusler compound CsK2⁢Sb at different compressive strains. This material exhibits a valence band structure with significant effective mass anisotropy, forming tubelike energy isosurfaces below the band edge, akin to that of two-dimensional (2D) systems. Such systems can have a large number of high-mobility charge carriers and a beneficial density of states profile. In the calculations, we predicted a maximum p-type figure of merit (𝑧⁢𝑇) of 2.6 at 800 K, in line with previous predictions of high 𝑧⁢𝑇. This high 𝑧⁢𝑇 arises from the low lattice thermal conductivity of 0.35 Wm−1K−1 and the beneficial electronic band structure. The high density of states significantly increased the electron-scattering space, but this effect was largely compensated by reduced scattering rates of electrons with large momentum 𝐪. We further explored the effect of enhancing the low-dimensionality through compressive strain. This increased the p-type power factor by up to 66%; partly due to more strongly pronounced 2D features of the valence band, but primarily due to increased Fermi velocities. However, compressive strain also increased phonon velocities and hence the lattice thermal conductivity. The maximum p-type 𝑧⁢𝑇 thus only increased slightly, to 2.7 at 1% compressive strain. In the conduction band, strain aligned the Γ- and X-centered valleys, resulting in the optimal n-type 𝑧⁢𝑇 increasing from 0.9 to 2.3 at 2% compressive strain. Thus highly strained CsK2⁢Sb has the potential for both good p- and n-type thermoelectricity.

• Morton, William James; Melau, Jørgen; Olsen, Roar A.; Løvvik, Ole Martin; Hisdal, Jonny & Søvik, Signe (2025). Thermal physiology of open water wetsuited swimming: A cohort study. Temperature. ISSN 2332-8940. 12(3), s. 245–263. doi: 10.1080/23328940.2025.2479893. Fulltekst i vitenarkiv Vis sammendrag

  Swimming in cold water is intrinsically unsafe. One of the threats is a fall in deep-body temperature, which adversely affects all body systems and increases the risk of death. Wetsuits mitigate, but do not negate this threat. Environmental conditions may confound findings from laboratory studies or mathematical models. The study aimed to elucidate associations and patterns of deep-body temperature change in open water wetsuited swimmers, thus facilitating risk assessment and improving swimmer safety. In this exploratory cohort study, following collection of anthropomorphic data including a Dual-energy X-ray Absorptiometry scan, deep-body temperature was continuously measured in 76 open water swims by 31 wetsuited swimmers in water temperatures ranging from 8.4°C to 24.5°C. The temperature trajectories were analyzed by piece-wise and linear mixed model regression. Registered with clinicaltrials.gov NCT06685627. Following immersion, there was a tri-phasic deep-body temperature trajectory, although not all phases were present in all swims: an initial rise, then a plateau phase and then thermal decompensation. Water temperature was correlated with the duration of these phases, as was body habitus for the initial rise. Minimum deep-body temperature was correlated with pre-swim temperature. Despite environmental and individual variations, this paper identified a tri-phasic deep-body temperature trajectory for wetsuited swimmers and proposed physiological mechanisms that may account for them. The tri-phasic pattern of an initial rise, a plateau phase and then thermal decompensation, may be useful in assessing the risks of open water swimming and may facilitate development and validation of deep-body temperature models for wetsuited swimmers.

• Grimnes, Øven Andreas; Snyder, G. Jeffrey; Løvvik, Ole Martin & Berland, Kristian (2024). Thermoelectric transport of strained CsK2Sb: Role of momentum-dependent scattering in low-dimensional Fermi surfaces. arXiv.org. ISSN 2331-8422. doi: 10.48550/arXiv.2412.01681. Fulltekst i vitenarkiv
• Morton, William James; Melau, Jørgen; Olsen, Roar A.; Løvvik, Ole Martin; Hisdal, Jonny & Søvik, Signe (2024). Manual Dexterity in Open-Water Wetsuited Swimmers: A Cohort Crossover Study. International Journal of Sports Physiology and Performance (IJSPP). ISSN 1555-0265. 20(2), s. 213–223. doi: 10.1123/ijspp.2024-0100. Fulltekst i vitenarkiv Vis sammendrag

  Purpose: Laboratory studies have demonstrated that manual dexterity decreases with increasing cold, which may adverselyaffect performance. Dexterity may be impaired by cooling of the hand, cooling of the lower motor neurons, and cognitiveimpairment. Wetsuits are commonly used in open-water swimming and are mandated in some situations. This study investigatesthe effects of cold-water wetsuited swimming on dexterity. Methods: Five male and 4 female trained swimmers were recruited forthis cohort crossover study. Following dual-energy X-ray absorptiometry scans to determine body composition, they swam in afreshwater lake on 7 occasions with water temperatures between 24.5 °C and 8.4 °C. Dexterity was measured preswim andpostswim with a “nut–washer–bolt assembly time test” and cognition with a Stroop test. Core and peripheral body temperatureswere continuously monitored. Effects were analyzed by linear mixed-model regression. Results: Pre–post swim difference intime to complete the nut–bolt assembly increased as water temperatures decreased (1.0 s, 95% CI, 0.5–1.5 per 1 °C, P < .0001;R2 = .456), to a maximum of 14.7 seconds (95% CI, 3.3–26.0). This represented a 47.5% increase in assembly time from 24.5 °Cto 8.4 °C, which we consider to be of practical significance. Decreased dexterity was associated with decreased forearm andscapular temperature and decreased cognitive function. Body composition did not affect dexterity, cognitive function, or bodytemperature during swims. Water temperature did not affect swim speed. Conclusions: Despite the use of wetsuits, manualdexterity decreased with cold-water swimming. Swimmers, triathletes, and event organizers should consider the implications forsafety, performance, and equipment utilization.

• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2023). Lattice Thermal Conductivity from First Principles and Active Learning with Gaussian Process Regression. arXiv.org. ISSN 2331-8422. doi: 10.48550/arXiv.2309.06786. Fulltekst i vitenarkiv
• Amici, Julia; Asinari, Pietro; Ayerbe, Elixabete; Barboux, Philippe; Bayle-Guillemaud, Pascale & Behm, R. Juergen [Vis alle 49 forfattere av denne artikkelen] (2022). A Roadmap for Transforming Research to Invent the Batteries of the Future Designed within the European Large Scale Research Initiative BATTERY 2030+. Advanced Energy Materials. ISSN 1614-6832. 12. doi: 10.1002/aenm.202102785. Fulltekst i vitenarkiv Vis sammendrag

  This roadmap presents the transformational research ideas proposed by “BATTERY 2030+,” the European large-scale research initiative for future battery chemistries. A “chemistry-neutral” roadmap to advance battery research, particularly at low technology readiness levels, is outlined, with a time horizon of more than ten years. The roadmap is centered around six themes: 1) accelerated materials discovery platform, 2) battery interface genome, with the integration of smart functionalities such as 3) sensing and 4) self-healing processes. Beyond chemistry related aspects also include crosscutting research regarding 5) manufacturability and 6) recyclability. This roadmap should be seen as an enabling complement to the global battery roadmaps which focus on expected ultrahigh battery performance, especially for the future of transport. Batteries are used in many applications and are considered to be one technology necessary to reach the climate goals. Currently the market is dominated by lithium-ion batteries, which perform well, but despite new generations coming in the near future, they will soon approach their performance limits. Without major breakthroughs, battery performance and production requirements will not be sufficient to enable the building of a climate-neutral society. Through this “chemistry neutral” approach a generic toolbox transforming the way batteries are developed, designed and manufactured, will be created. © 2022 The Authors. Advanced Energy Materials published by Wiley-VCH GmbH

• Mayandi, Jeyanthinath; Schrade, Matthias; Ponniah, Vajeeston; Stange, Marit Synnøve Sæverud; Lind, Anna Maria & Sunding, Martin Fleissner [Vis alle 13 forfattere av denne artikkelen] (2022). High entropy alloy CrFeNiCoCu sputter deposited films: Structure, electrical properties, and oxidation. Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. ISSN 0734-2101. 40(2). doi: 10.1116/6.0001394. Fulltekst i vitenarkiv Vis sammendrag

  High entropy alloy (HEA) films of CrFeCoNiCu were deposited by sputtering. Their structure was characterized and their electric transport properties were studied by temperature-dependent Hall and Seebeck measurements. The HEA films show a solid solution with an fcc structure. The residual electrical resistivity of the films is around 130 μΩ cm, which is higher than the Mott limit for a metal while the temperature dependence of the resistivity above 30 K is metal-like but with a small temperature coefficient of resistivity (2 ppm/K). The dominant scattering mechanism of charge carriers is alloy scattering due to chemical disorder in the HEA. The Hall coefficient is positive while the Seebeck coefficient is negative. This is interpreted as arising from an electronic structure where the Fermi level passes through band states having both holes and electrons as indicated by band structure calculations. Below 30 K, the conduction is discussed in terms of weak localization and Kondo effects. The HEA structure appears stable for annealing in vacuum, while annealing in an oxygen-containing atmosphere causes the surface to oxidize and grow a Cr-rich oxide on the surface. This is then accompanied by demixing of the HEA solid solution and a decrease in the effective resistance of the film.

• Bazioti, Kalliopi; Løvvik, Ole Martin; Poulia, Anthoula; Carvalho, Patricia Almeida; Azar, Amin S. & Mikheenko, Pavlo [Vis alle 8 forfattere av denne artikkelen] (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, s. 1–12. doi: 10.1016/j.jallcom.2022.164724. Fulltekst i vitenarkiv Vis sammendrag

  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, s. 1–6. doi: 10.1016/j.mtla.2022.101461. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2022). Attaining Low Lattice Thermal Conductivity in Half-Heusler Sublattice Solid Solutions: Which Substitution Site Is Most Effective? Electronic Materials. 3(1), s. 1–14. doi: 10.3390/electronicmat3010001. Fulltekst i vitenarkiv Vis sammendrag

  Low thermal conductivity is an important materials property for thermoelectricity. The lattice thermal conductivity (LTC) can be reduced by introducing sublattice disorder through partial isovalent substitution. Yet, large-scale screening of materials has seldom taken this opportunity into account. The present study aims to investigate the effect of partial sublattice substitution on the LTC. The study relies on the temperature-dependent effective potential method based on forces obtained from density functional theory. Solid solutions are simulated within a virtual crystal approximation, and the effect of grain-boundary scattering is also included. This is done to systematically probe the effect of sublattice substitution on the LTC of 122 half-Heusler compounds. It is found that substitution on the three different crystallographic sites leads to a reduction of the LTC that varies significantly both between the sites and between the different compounds. Nevertheless, some common criteria are identified as most efficient for reduction of the LTC: The mass contrast should be large within the parent compound, and substitution should be performed on the heaviest atoms. It is also found that the combined effect of sublattice substitution and grain-boundary scattering can lead to a drastic reduction of the LTC. The lowest LTC of the current set of half-Heusler compounds is around 2 W/Km at 300 K for two of the parent compounds. Four additional compounds can reach similarly low LTC with the combined effect of sublattice disorder and grain boundaries. Two of these four compounds have an intrinsic LTC above ∼15 W/Km, underlining that materials with high intrinsic LTC could still be viable for thermoelectric applications.

• Mayandi, Jeyanthinath; Finstad, Terje Gunnar; Dahl, Øystein; Ponniah, Vajeeston; Schrade, Matthias & Løvvik, Ole Martin [Vis alle 8 forfattere av denne artikkelen] (2022). Thin films made by reactive sputtering of high entropy alloy FeCoNiCuGe: Optical, electrical and structural properties. Thin Solid Films. ISSN 0040-6090. 744(139083). doi: 10.1016/j.tsf.2022.139083. Fulltekst i vitenarkiv Vis sammendrag

  Films were reactively sputtered from a high entropy alloy (HEA) FeCoNiCuGe target in an Ar/O2 plasma. The case of zero O2 gas flow yielded HEA films of FeCoNiCuGe. These as-deposited HEA films have a face centered cubic (FCC) structure, showing a texture with columnar grains containing many planar defects. The residual electrical resistivity of the films is around 225 μΩcm and the temperature dependence of the resistivity is metal-like. The temperature coefficient of resistivity is small (4.5 ppm/K). The Hall coefficient is positive while the Seebeck coefficient is negative. This is interpreted as arising from an electronic structure having both holes and electrons at the Fermi level as indicated by band structure calculations. The HEA FCC structure is unstable upon annealing in forming gas and showed demixing. Annealing in O2 also yielded inhomogeneous oxides, with a thick layer of CuO growing on the surface. The cases of reactive sputtering with an oxygen flow yielded oxides that are either nanocrystalline or amorphous dependent upon the sputter conditions. These can be classified as high entropy oxides (HEO) and have an optical bandgap around 1.9 eV and high transmission in the infrared region. The amorphous HEO has an electrical conduction interpreted as due to variable range hopping described by the Efros–Shklovskii theory. The HEO films were reduced in forming gas. For the amorphous HEO film, the reduction at 300–500 °C yielded hexagonal Ni5Ge2 and an FCC phase. For the nanocrystalline HEO, reduction resulted in creation of FCC and body centered cubic HEA metal phases.

• Berland, Kristian; Løvvik, Ole Martin & Tranås, Rasmus André (2021). Discarded gems: Thermoelectric performance of materials with band gap emerging at the hybrid-functional level. Applied Physics Letters. ISSN 0003-6951. 119(8). doi: 10.1063/5.0058685. Fulltekst i vitenarkiv Vis sammendrag

  A finite electronic band gap is a standard filter in high-throughput screening of materials using density functional theory (DFT). However, because of the systematic underestimation of band gaps in standard DFT approximations, a number of compounds may be incorrectly predicted metallic. In a more accurate treatment, such materials may instead appear as low band gap materials and could have good thermoelectric properties if suitable doping is feasible. To explore this possibility, we performed hybrid functional calculations on 1093 cubic materials listed in the MATERIALS PROJECT database with four atoms in the primitive unit cell, spin-neutral ground state, and a formation energy within 0.3 eV of the convex hull. Out of these materials, we identified eight compounds for which a finite band gap emerges. Evaluating electronic and thermal transport properties of these compounds, we found the compositions MgSc2Hg and Li2CaSi to exhibit promising thermoelectric properties. These findings underline the potential of reassessing band gaps and band structures of compounds to identify additional potential thermoelectric materials.

• Mayandi, Jeyanthinath; Finstad, Terje Gunnar; Stange, Marit Synnøve Sæverud; Vasquez, Geraldo Cristian; Sunding, Martin Fleissner & Løvvik, Ole Martin [Vis alle 8 forfattere av denne artikkelen] (2021). Controlling the Electrical Properties of Reactively Sputtered High Entropy Alloy CrFeNiCoCu Films. Journal of Electronic Materials. ISSN 0361-5235. 51, s. 803–812. doi: 10.1007/s11664-021-09343-3. Fulltekst i vitenarkiv Vis sammendrag

  Oxide-containing films were made by reactively sputtering a high-entropy alloy target of CrFeCoNiCu. We report on a wide range of changes to the electrical properties made by different heat treatments in oxidizing and reducing atmospheres, respectively. We combine temperature-dependent Hall effect measurements down to 10 K to study the transport mechanisms and correlate that with structural measurements by x-ray diffraction and scanning electron microscopy. The measured/effective resistivity could be varied between 1.3 × 10−4 Ω cm and 1.2 × 10−3 Ω cm by post-deposition processing. The temperature coefficient of resistivity could be varied between − 1.2 × 10−3 K−1 through 0 and to + 0.7 × 10−3 K−1. The key to the variation is controlling the morphology and topology of the film. The conduction of charge carriers is dominated by the relative contribution of weak localization and alloy scattering by varying the degree of disorder in the metallic high-entropy alloy and its topology.

• Bernal, Fabian Leonardo Martinez; Lundvall, Fredrik; Kumar, Susmit; Hansen, Per-Anders S.; Wragg, David S. & Fjellvåg, Helmer [Vis alle 7 forfattere av denne artikkelen] (2021). Jahn-Teller active fluoroperovskites ACrF3 (A=Na+, K+): Magnetic and thermo-optical properties. PHYSICAL REVIEW MATERIALS. 5(6). doi: 10.1103/PhysRevMaterials.5.064420. Fulltekst i vitenarkiv Vis sammendrag

  Chromium (II) fluoroperovskites A CrF 3 ( A = Na + , K + ) are strongly correlated Jahn-Teller active materials at low temperatures. In this paper, we examine the role that the A -site ion plays in this family of fluoroperovskites using both experimental methods (x-ray diffraction, optical absorption spectroscopy, and magnetic fields) and density functional theory simulations. Temperature-dependent optical absorption experiments show that the spin-allowed transitions E 2 and E 3 only merge completely for A = Na at 2 K. Field-dependent optical absorption measurements at 2 K show that the oscillating strength of the spin-allowed transitions in NaCrF 3 increases with increasing applied field. Direct magneto-optical correlations suppress the spin-flip transitions for KCrF 3 below its Néel temperature. In NaCrF 3 the spin-flip transitions vanish abruptly below 9 K revealing magneto-optical correlations possibly linked to crystal structure changes. This suggests that as the long range ordering is reduced, local Jahn-Teller effects in the individual CrF 4 − 6 octahedra take control of the observed behavior. Our results show clear deviation from the pattern found for the isoelectronic A x MnF 3 + x system. The size of the A -site cation is shown to be central in dictating the physical properties and phase transitions in A CrF 3 , opening up the possibility of varying the composition to create novel states of matter with tunable properties.

• Graff, Joachim Seland; Schuler, Raphael; Song, Xin; Castillo-Hernandez, Gustavo; Skomedal, Gunstein & Enebakk, Erik [Vis alle 11 forfattere av denne artikkelen] (2021). Fabrication of a Silicide Thermoelectric Module Employing Fractional Factorial Design Principles. Journal of Electronic Materials. ISSN 0361-5235. 50, s. 4041–4049. doi: 10.1007/s11664-021-08902-y. Fulltekst i vitenarkiv Vis sammendrag

  Thermoelectric modules can be used in waste heat harvesting, sensing, and cooling applications. Here, we report on the fabrication and performance of a four-leg module based on abundant silicide materials. While previously optimized Mg2Si0.3Sn0.675Bi0.025 is used as the n-type leg, we employ a fractional factorial design based on the Taguchi methods mapping out a four-dimensional parameter space among Mnx-εMoεSi1.75−δGeδ higher manganese silicide compositions for the p-type material. The module is assembled using a scalable fabrication process, using a Cu metallization layer and a Pb-based soldering paste. The maximum power output density of 53 μW cm–2 is achieved at a hot-side temperature of 250 °C and a temperature difference of 100 °C. This low thermoelectric output is related to the high contact resistance between the thermoelectric materials and the metallic contacts, underlining the importance of improved metallization schemes for thermoelectric module assembly.

• Tranås, Rasmus André; Løvvik, Ole Martin; Tomic, Oliver & Berland, Kristian (2021). Lattice thermal conductivity of half-Heuslers with density functional theory and machine learning: Enhancing predictivity by active sampling with principal component analysis. Computational Materials Science. ISSN 0927-0256. 202. doi: 10.1016/j.commatsci.2021.110938. Fulltekst i vitenarkiv Vis sammendrag

  Low lattice thermal conductivity is essential for high thermoelectric performance of a material. Lattice thermal conductivity is often computed using density functional theory (DFT), typically at a high computational cost. Training machine learning models to predict lattice thermal conductivity could offer an effective procedure to identify low lattice thermal conductivity compounds. However, in doing so, we must face the fact that such compounds can be quite rare and distinct from those in a typical training set. This distinctness can be problematic as standard machine learning methods are inaccurate when predicting properties of compounds with features differing significantly from those in the training set. By computing the lattice thermal conductivity of 122 half-Heusler compounds, using the temperature-dependent effective potential method, we generate a data set to explore this issue. We first show how random forest regression can fail to identify low lattice thermal conductivity compounds with random selection of training data. Next, we show how active selection of training data using feature and principal component analysis can be used to improve model performance and the ability to identify low lattice thermal conductivity compounds. Lastly, we find that active learning without the use of DFT-based features can be viable as a quicker way of selecting samples.

• Polfus, Jonathan; Peters, Thijs; Bredesen, Rune & Løvvik, Ole Martin (2021). Vacancy diffusion in palladium hydrides. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 23(24), s. 13680–13686. doi: 10.1039/d1cp01960k. Fulltekst i vitenarkiv Vis sammendrag

  The self-diffusion coefficients of palladium in PdHx (x = 0, 0.25, 0.5, 0.75, 1) were studied using density functional theory to obtain the required thermodynamic and kinetic parameters. The enthalpy of migration decreased from 0.95 eV for Pd to 0.78 eV for PdH. The enthalpy of vacancy formation exhibited a substantial decrease from about 1.1 eV in Pd to 0.4 eV in PdH, which was ascribed to successive filling of antibonding states weakening the Pd–Pd bonds. Concurrently, the Arrhenius pre-exponential was significantly reduced from 4.75 × 10−3 cm2 s−1 for Pd to 5.67 × 10−9 cm2 s−1 for PdH due to softening of the vibrational modes that determine the entropy of vacancy formation and initial/transition state frequencies. A linear correlation between the logarithm of the pre-exponential and the activation energy was interpreted as enthalpy–entropy compensation (Meyer–Neldel rule). The Pd self-diffusion coefficients in the hydrides were within 1 order of magnitude of that in pure palladium above 200 °C for hydrogen pressures up to at least 107 Pa.

Se alle arbeider i NVA

• Løvvik, Ole Martin (2026). Spille klarinett med helium. [Radio]. NRK P2. doi: https:/radio.nrk.no/podkast/abels_taarn/l_c5c3e976-8c65-4426-83e9-768c65142664. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Hvordan låter en klarinett som spilles med helium? Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Accelerated discovery of functional materials at the atomistic scale. doi: https:/eu-mace.eu/event/5862:training-school-2026-accelmaps-accelerating-energy-materials-development-from-legacy-labs-to-material-accelerationplatforms.html. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Solceller og strømstøtte. [TV]. NRK1. doi: https:/tv.nrk.no/serie/dagsnytt-atten-tv/sesong/202606/episode/NNFA56060926. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Solcelletak er det nesten ingen som vil ha lenger. [Internet]. www.nrk.no. Fulltekst i vitenarkiv Vis sammendrag

  Interessen for solcellepanel på taket har stupt. Bransjen snakker om full krise. Strømstøtte og norgespris får skylda, men regjeringen er helt uenig.

• Løvvik, Ole Martin (2026). Norgespris er aktiv dødshjelp. [TV]. NRK1. doi: https:/tv.nrk.no/se?v=NNFA19060726&t=791s. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Na-ion batteries – what is their current status, and what is their future potential? Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Development of new materials with modern digital tools – the Emperor’s new clothes? Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2026). Development of new materials with beneficial properties for thermoelectricity. [Internet]. ThermoBuild Brief. doi: https:/www.unav.edu/documents/d/departamento-de-construccion-instalaciones-estructuras/bites-newsletter-2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Bratlie, Sigrid; Goodwin, Morten & Vidnes, Aksel Kjær (2026). Årets forskningsgjennombrudd - Abels tårn - NRK Radio. [Radio]. NRK P2. Fulltekst i vitenarkiv Vis sammendrag

  Torkild Jemterud og hans panel ser på 2025s forskningsresultater. Har datamaskiner bestått Turing-testen? Lever nakenrotter evig?

• Jemterud, Torkild; Bjorå, Charlotte Sletten; Görbitz, Carl Henrik; Bøhn, Einar Duenger; Dietrichs, Erik Sveberg & Paus-Knudsen, Julie Sørlie [Vis alle 8 forfattere av denne artikkelen] (2025). Abels tårns ekstrasending. [Radio]. P2. doi: https:/radio.nrk.no/podkast/abels_taarn/sesong/2025. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhard; Kušnír, Jakub & Grabek, Tomas [Vis alle 11 forfattere av denne artikkelen] (2025). Phase change materials for elastocaloric cooling. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Stange, Marit Synnøve Sæverud; Bumke, Lars; Quandt, Eckhardt; Kusnir, Jakub & Grabek, Tomas [Vis alle 10 forfattere av denne artikkelen] (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. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2025). Kan vi hente verdifulle mineraler fra månen? - Abels tårn - NRK Radio. [Radio]. NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2025). Tellur - Grunnstoffene. Fulltekst i vitenarkiv Vis sammendrag

  Tellur er en skikkelig luring. Dette grunnstoffet som ligger helt i skjæringspunktet mellom å være en halvleder og en hel-leder (eller metall som det jo også heter) gir oppgav til mange interessante fysiske fenomener, og er en av grunnene til at det er dagens gjest, Kristian Berland fra NMBU, har det som sitt favorittgrunnstoff. Ikke… Fortsett å lese Tellur

• Uggerud, Hilde Thelle; Skomedal, Gunstein; Løvvik, Ole Martin & Runde, Birte (2025). Livepod på NILU - Tungmetaller på avveie, med Hilde Uggerud. doi: https:/youtu.be/8V63hTgz9B8?si=mb_1c-48wEoMWPNW. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Bjorå, Charlotte Sletten; Jemterud, Torkild; Løvvik, Ole Martin & Sletsjøe, Arne Bernhard (2024). Abels tårn. [Radio]. NRK P2. Fulltekst i vitenarkiv
• Sagvolden, Espen; Løvvik, Ole Martin; Fertitta, Edoardo; Roshaninejad, Parisa; Habicht, Klaus & Quintero-Castro, Diana Lucia [Vis alle 7 forfattere av denne artikkelen] (2024). Ab-initio calculations of anharmonicity in thermoelectric materials via the stochastic temperature-dependent effective potential (sTDEP) method. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2024). Lyddemping i tømmervegger, holdbarhet av hamptau og den høyeste mulige temperaturen. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Quintero-Castro, Diana Lucia; Habicht, Klaus; kojda, Danny; Keller, Thomas; Bourdarot, Frederic & Løvvik, Ole Martin [Vis alle 10 forfattere av denne artikkelen] (2024). Probing Phonon Lifetimes in Strongly Anharmonic SrTiO3. Fulltekst i vitenarkiv
• Skomedal, Gunstein & Løvvik, Ole Martin (2024). Podcast Grunnstoffene - en vimsete reise gjennom det periodiske system. [Internet]. Podkast. Fulltekst i vitenarkiv Vis sammendrag

  En podcast om alle grunnstoffene i det periodiske system, hvert grunnstoff én episode, som publiserer 1-2 episoder per måned.

• Vestre, Katharina; Mossige, Joachim; Løvvik, Ole Martin & Jemterud, Torkild (2024). Abels tårn 12.1.2024. [Radio]. Abels tårn NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2024). Hvor tynt kan gull bli og hvorfor er jorda full av tunge grunnstoffer? [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Grimenes, Øven Andreas; Løvvik, Ole Martin & Berland, Kristian (2024). The Importance of Electronic Relaxation Times in Complex Fermi Surfaces. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2024). Sykling, radongass og oversikt over hva vi vet. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Grimenes, Øven Andreas; Løvvik, Ole Martin; Snyder, G. Jeffrey & Berland, Kristian (2024). Electron scattering in materials with extended Fermi surfaces. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Berland, Kristian; Grimenes, Øven Andreas & Løvvik, Ole Martin (2024). New materials with very low lattice conductivity from first principles and machine learning. Fulltekst i vitenarkiv
• Roshaninejad, Parisa; Quintero-Castro, Diana Lucia; Løvvik, Ole Martin; Habicht, Klaus; kojda, Danny & Fertitta, Edoardo [Vis alle 7 forfattere av denne artikkelen] (2024). Phonon lifetime studies in thermoelectric materials by combining inelastic neutron scattering and ab-initio calculations. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2023). Hvor dramatisk er det å la kjøleskapdøra stå åpen flere minutter? [TV]. Intervju i Praktisk Info med Jon Almaas, TV Norge. Fulltekst i vitenarkiv
• Delsett, Lene Liebe; Løvvik, Ole Martin; Strumke, Inga & Jemterud, Torkild (2023). Abels tårn - Den viktigste forskninga i 2022. [Radio]. NRK P2. Fulltekst i vitenarkiv
• Rahman, Jamil Ur; Gunnæs, Anette Eleonora; Finstad, Terje Gunnar; Løvvik, Ole Martin & Carvalho, Patricia Almeida (2023). Structure of a high entropy Heusler antimonide. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2023). Screening of low lattice thermal conductivity materials using active learning. Fulltekst i vitenarkiv
• Marthinsen, Astrid; Marchand, Daniel; Ringdalen, Inga Gudem; Zhang, Kai; Løvvik, Ole Martin & Du, Qiang [Vis alle 11 forfattere av denne artikkelen] (2023). Transforming ideas into reality: exploring the power of numerical modelling & simulation tools for material and process development. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Grimenes, Øven Andreas; Løvvik, Ole Martin & Berland, Kristian (2023). Complex Fermi surfaces for high ZT. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2023). Abels tårns årskavalkade – nye materialer og maskinlæring. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Rønning, Sissel Beate; Uggerud, Einar & Løvvik, Ole Martin (2023). Abels tårn - Hvordan bør oppvaskkosten oppbevares? [Radio]. NRK Radio. Fulltekst i vitenarkiv Vis sammendrag

  - Er selv brød ultraprosessert, og gjør det noe? - Lading av powerbank på tur - Bør man la oppvaskkosten ligge i vasken eller henge den opp? - Hva er best: oppvaskkost eller svamp? - Hva ville en kjemiker kunne lage hvis hen ble kasta 2000 år tilbake i tid? - Hvordan ville det vært å bevege seg rundt inni jorda, dersom den var hul? - Er kværna rødt kjøtt mer usunt enn en hel biff? - Kan man lage en stjerne av vann? I panelet: Sissel Beate Rønning - Genteknolog og matforsker Einar Uggerud - Kjemiker Ole Martin Løvvik - Fysiker

• Løvvik, Ole Martin (2023). Plast som leder strøm og andre nye materialer for det grønne skiftet. [Radio]. Intervju i Ekko, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2023). Storsatsing på utvikling av materialer med automatisering og kunstig intelligens. [Radio]. Intervju i Abels tårn. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2023). Om varmepumper, magnetisme og tyngdekraft. [Radio]. Intervju i Abels tårn. Fulltekst i vitenarkiv
• Finstad, Terje Gunnar; Mayandi, Jeyanthinath; Soltani, Nayereh; Pokle, Anuj; Løvvik, Ole Martin & Carvalho, Patricia Almeida (2023). TiFe2Si Thin Films. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2023). Norwegian efforts towards a materials acceleration platform: combining high-throughput experiments, modelling, and machine learning/artificial intelligence. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2022). Finding Low Lattice Thermal Conductivity Compounds in Materials Space: Machine Learning with Active Sampling. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Hvordan få strøm fra varme – uten bevegelige deler? Fulltekst i vitenarkiv
• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2022). Alloying leads to drastic reduction of lattice thermal conductivity of half-Heusler compounds. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Bør du lukke døra til komfyren når den er ferdig med å steke? [TV]. Intervju i Praktisk Info med Jon Almaas, TV Norge. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Er virkelig norsk olje verdens reneste? [Radio]. Intervju i Abels bakgård, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Vind, vann og sol kan stille hele verdens energibehov innen 2050. [Radio]. Intervju i Abels bakgård, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Thermoelectrics of alloys and intermetallic materials: potential benefits and challenges of using SPS. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Løvvik, Ole Martin & Berland, Kristian (2022). Material Informatics: Machine Learning with Active Sampling for Small Training Sets. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Schrade, Matthias; Grimenes, Øven Andreas; Tranås, Rasmus André & Berland, Kristian (2022). Predictive screening for thermoelectric properties using atomic-scale simulations and machine learning tools. Fulltekst i vitenarkiv
• Løvvik, Ole Martin; Carvalho, Patricia A.; Stange, Marit Synnøve Sæverud; Sunding, Martin Fleissner; Rajput, Kalpna & Larsen, Aleksander Amble [Vis alle 9 forfattere av denne artikkelen] (2022). Elastocaloric cooling with TiNiCuZr alloys? Fulltekst i vitenarkiv
• Grimenes, Øven Andreas; Løvvik, Ole Martin & Berland, Kristian (2022). Hybrid Functional Screening Identifies Previously Discarded Thermoelectric Materials. Fulltekst i vitenarkiv
• Grimenes, Øven Andreas; Løvvik, Ole Martin & Berland, Kristian (2022). More than 130 new low bandgap materials identified in a hybrid functional screening study – some with very promising thermoelectric properties. Fulltekst i vitenarkiv
• 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. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Berland, Kristian; Tomic, Oliver & Løvvik, Ole Martin (2022). Discovering Energy Materials: Low Thermal Conductivity Thermoelectric Compounds and Barocaloric Compounds. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Jordvarme, kjernekraft og batterier. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2022). Abels tårn: Artig underholdning eller nyttig kunnskap? Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Volum av Li-batterier og horisontale raketter. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Magneter, solceller og isbiter. [Radio]. Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Screening of materials for thermoelectric conversion of heat into electricity. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Vi skal utvikle materialer for fornybar energi ti ganger raskere enn i dag. [Journal]. Apollon : Forskningsmagasin for Universitetet i Oslo. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Casting Materials Acceleration Platform and the accelerated search for thermoelectric materials. Fulltekst i vitenarkiv
• Mayandi, Jeyanthinath; Finstad, Terje; Stange, Marit Synnøve Sæverud; Vasque, Giovanni; Sunding, Martin Fleissner & Løvvik, Ole Martin [Vis alle 8 forfattere av denne artikkelen] (2021). Engineering Electrical Properties of Reactively Sputtered High Entropy Alloy CrFeNiCoCu Films. Fulltekst i vitenarkiv Vis sammendrag

  Oxide containing films were deposited by reactive sputtering using a high entropy alloy (HEA) target made of equal concentrations of the five 3d-transion metals: Cr, Fe, Co, Ni, and Cu. We report on controlled alterations to the electrical properties made by post-deposition heat treatments in oxidizing and reducing atmospheres respectively. The temperature coefficient of resistivity of the films could be varied between -1.2×10-3 K-1 through 0 and to +0.7×10-3 K-1, while the measured effective resistivity could be varied between 1.3×10-4 Ωcm and 1.2×10-3 Ωcm by post deposition processing. To study the transport mechanisms, we performed temperature dependent Hall effect measurements down to 10 K. We correlated the electrical behavior with structural measurements by a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS) for elemental mapping at various length scales and secondary ions mass spectroscopy (SIMS). The key to engineering the resistivity is controlling the topology of the film. The topology of the as- deposited thin films can be controlled by the oxygen flow during reactive sputtering as the most important parameter. For zero oxygen flow we have obtained a homogenous HEA film having a FCC structure with the CrFeNiCoCu target. For high oxygen flow we have observed a high entropy oxide with a rock salt crystal structure. Here we report on the case of intermediate flow of oxygen. The as-deposited structure is then complex. There are nano sized regions with oxides and regions with FCC HEA alloys with different compositions of all the 3d-metals but also supersaturated with oxygen. The topology of these regions, and also their concentration, can be altered by post-deposition heat treatment. The transport in the HEA regions are dominated by alloy scattering. The potential in the FCC HEA has disorder due to the random mixing of the elements, which also gives distortion of the individual atom sites. This gives resistivities above the Mott- Ioffe-Regel limit while still having a positive TCR. These disorder effects will be further enhanced by the uptake of oxygen atoms. For these cases one gets weak localization, yielding a negative TCR. The oxides may be insulating but may also conduct by variable range hopping of the Efros–Shklovskii-type or the Mott- type yielding characteristic negative TCR. The post-deposition yields oxide segregation, of for example of spinel type containing Cr. This reduce the entropy and stability of the metal alloy, creating FCC and BCC metal alloys of different compositions. In the case of reducing the heat treatment in a reducing atmosphere, the oxides are reduced. The experimental resistivities are in excellent agreement with the model for the conduction.

• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Azar, Amin S.; Mikheenko, Pavlo & Diplas, Spyridon [Vis alle 7 forfattere av denne artikkelen] (2021). Advanced Scanning Transmission Electron Microscopy investigations of FeCoNi(AlMn)x high-entropy alloy: nanoscale structure and impact on magnetic properties. Fulltekst i vitenarkiv
• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Carvalho, Patricia Almeida; Azar, Amin S. & Mikheenko, Pavlo [Vis alle 8 forfattere av denne artikkelen] (2021). STEM-EELS investigations and Lorentz microscopy unravelling the structural evolution of FeCoNi(AlMn)x high-entropy alloy and its impact on magnetic properties. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Løvvik, Ole Martin; Tomic, Oliver & Berland, Kristian (2021). Active sample selection for finding low lattice thermal conductivity materials using machine learning. Fulltekst i vitenarkiv
• Azar, Amin S.; Schrade, Matthias; Graff, Joachim Seland; Flage-Larsen, Espen; Løvvik, Ole Martin & Belle, Branson [Vis alle 8 forfattere av denne artikkelen] (2021). Structural and magnetic performance of soft magnets based on FeCoNiMnAl additively manufactured high entropy alloys. Fulltekst i vitenarkiv
• Bazioti, Kalliopi; Poulia, Anthoula; Løvvik, Ole Martin; Azar, Amin S.; Mikheenko, Pavlo & Diplas, Spyridon [Vis alle 7 forfattere av denne artikkelen] (2021). Structural evolution of FeCoNi(AlMn)x high-entropy alloy and impact on magnetic properties: nano-scale STEM-EELS investigations. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Pepperkakehus, stearinlys og sprø ribbe. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Løvvik, Ole Martin (2021). Effektivitet og pris av batterier i batteribanker og nettbrett. [Radio]. Intervju i Abels tårn, NRK P2. Fulltekst i vitenarkiv
• Tranås, Rasmus André; Berland, Kristian; Løvvik, Ole Martin & Tomic, Oliver (2021). Fingerprints of low lattice thermal conductivity compounds: half-Heusler case study and beyond. Fulltekst i vitenarkiv
• Jemterud, Torkild; Danielsen, Anne; Brodal, Per; Løvvik, Ole Martin; Goodwin, Morten & Knudsen, Pål Moddi (2020). Abels tårn: En følsom AI tester visesang. Fulltekst i vitenarkiv Vis sammendrag

  Kan en AI lage bedre tekster enn en visesanger? Og bedre drinker enn en bartender? Vi tester begge deler. Prøvekanin er Pål Moddi Knudsen. En AI har tygd seg gjennom de gamle tekstene hans, og spytta ut en splitter ny. Dessuten - Hvorfor hører man bare bassen fra festen ved siden av? - Konsentrer man seg bedre med musikk? - Løper man raskere med musikk? - Hvorfor har vi så ulik musikksmak? - Hvorfor er Moddis gitar alltid sur? - Hvor varmt blir det i en peisovn? I panelet Visesanger Pål Moddi Knudsen Datalog Morten Goodwin Musikkviter Anne Danielsen Fysiker Ole Martin Løvvik Hjerneforsker Per Brodal

• Løvvik, Ole Martin & Vucetic, Vasilija (2025). First-principles study of structure and phase stability of Cu2AlMn Heusler alloy using TDEP and DFT. Universitetet i Oslo. Fulltekst i vitenarkiv
• Grimnes, Øven Andreas; Berland, Kristian & Løvvik, Ole Martin (2025). Scattering dependent electronic transport in thermoelectric materials with complex band structures. Norges miljø- og biovitenskapelige universitet (NMBU). ISSN 9788257523039. Fulltekst i vitenarkiv Vis sammendrag

  Thermoelectric (TE) materials, which can convert heat to electricity and vice versa, have great potential for energy harvesting from waste heat and have seen renewed interest in recent years. These materials are also used in many niche applications, such as electrical generators in remote locations, sensors, and cooling for medical and scientific equipment. With the advent of computational methods like density functional theory (DFT), modeling is becoming an increasingly more important tool in the TE field. Providing, among other things, electronic band structures and electronic transport properties, DFT combined with Boltzmann transport theory provides both predictive and explanatory power. A limiting factor, however, has long been the modeling of electron scattering, resulting in the use of coarse approximations like the constant relaxation time approximation or textbook results based on heavily simplified models. More accurate modeling and understanding of electronic scattering in complex materials and band structures could lift the field of TE and result in new and improved TE materials. To find suitable candidate materials for more detailed analysis, a highthroughput (HT) screening of the Materials Project database was performed. Based on criteria such as crystal structure complexity, elements, energy above convex hull, magnetic properties, and valence electron count, 6965 materials were selected. For more accurate band gap estimations, the MBJ functional was employed. This revealed band gaps in 189 materials predicted to be metallic with PBE, and an average band gap increase of 0.43 eV in 331 materials with narrow PBE band gaps. The electronic transport properties and thermoelectric figure of merit (zT) were calculated with a constant relaxation time (τ ) of 10 fs and with a lattice thermal conductivity (κℓ) of 5 W/mK for each material. Using the same, constant τ and κℓ for every material results in both false positives and negatives, but still yields a rough ranking on how applicable the electronic structure is for TE purposes. Based on the high-throughput results, two promising full-Heusler materials were selected for further investigation. CsK2Sb, a known photocatode material, has a complex band structure with features akin to those of two-dimensional (2D) quantum wells. The other material, Na2TlSb, also has a quasi-low-dimensional band structure, but one-dimensional (1D), resulting in a Fermi surface consisting of sheets. Both band structures have a rapidly increasing density of states (DOS) with high-mobility carriers close to the band gap, a favorable trait for thermoelectric materials. Despite high DOS generally being associated with excessive electron scattering, this was not found to be the case in these materials, counterintuitive to conventional wisdom. Both materials were also found to have very low κℓ, resulting in a predicted zT of 2.6 and 4.4 for CsK2Sb and Na2TlSb, respectively. Compressive strain was found to improve the electronic transport properties of CsK2Sb by enhancing the 2D features and reducing electron scattering, but also increased κℓ, resulting in only a marginally increased zT of 2.7 at 1% strain. The changes to materials properties and the resulting electronic scattering rates in strained CsK2Sb prompted further investigation. The materials properties of ZrNiSn were systematically adjusted, and the following changes to scattering rates were observed. While most materials properties changed scattering rates as expected, some gave less intuitive results. Other parameters relevant to scattering, such as carrier concentration (Nc) and temperature (T), were also investigated. In addition to directly affecting different scattering mechanisms, both Nc and T change the location of the Fermi level and the magnitude of free-carrier screening, creating highly interconnected results. The low scattering rates could also, in part, be explained by the exotic geometries of the Fermi surfaces. For momentum-dependent scattering mechanisms, the large separation in k-space prevented scattering between large parts of the surface. Further, the combination of wavefunction overlaps and the geometrical momentum relaxation time factor strongly reduced elastic scattering to large portions of the total scattering space. The results for both materials indicate that Fermi surfaces delocalized in k-space tend to reduce electronic scattering. These insights, combined with knowledge of how materials properties affect scattering, can help build understanding and intuition that can aid the discovery and design of new TE materials.

• Høylo-Rosenberg, Jørn-Marcus; Løvvik, Ole Martin & Persson, Clas (2022). An ab initio study of the band gaps of high-entropy silicides based on FeSi2. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  In this work we have set out to examine the band gaps of potential high-entropy stabilized transition metal silicides, based on the FeSi2 semiconductor. Here, we have performed a first principles study utilizing density functional theory in combination with the special quasi-random structures method. The band gaps has been evaluated primarily with the PBE GGA functional, but also the SCAN meta-GGA functional and hybrid functional HSE06 has been applied in this project. Potential alloys has been examined by generating a set of distinct supercells of the FeSi2 structure, where the iron sites are populated quasi-randomly by a combination of 3d transition metals. The alloys we have studied in this project are comprised of combinations of Cr, Fe, Mn, Ni, Co and Ti, most emphasis has been put on the Cr-Fe-Mn-Ni-Si system. In the (CrFeMnNi)Si2 composition, we can report several semiconducting supercells with band gaps ranging between 0 - 0.05 eV using PBE GGA. The band gaps displayed significant spin polarization, in the spin up direction most supercells pointed to a gap around 0.3 eV. Contrary, the band gaps in spin down varied between 0 - 0.05 eV. Accordingly, we found a finite magnetic moment in this alloy equal to 0.083 mu_B, this was attributed mainly to chromium and manganese atoms in the lattice. Successive simulations of alloys based on the Cr-Fe-Mn-Ni-Si system with non-equimolar distribution of 3d elements, resulted most frequently in half-metallic structures with a spin up band gap ranging between 0.1 eV and 0.5 eV. Of the different compositions we tested, the ones either rich in manganese and/or poor in chromium showed the most promise with respect to the band gap. In particular, we report a PBE total band gap equal to 0.1 eV in the Cr3Fe5Mn5Ni3Si32 composition. Lastly, we looked at compositions where either Cr, Mn or Ni were replaced by either cobalt or titanium. This yielded predominately metallic compounds, where the lack of band gaps could be ascribed to defect states at the band edges.

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