THELMA - termoelektriske materialer (avsluttet)

• Echevarria-Bonet, Cristina; Garrido-Alvarez, J.L.; Martinez-Blanco, D.; Gorria, P.; Sørby, Magnus Helgerud & Riktor, Marit Dalseth [Vis alle 8 forfattere av denne artikkelen] (2023). Anharmonicity effects and thermal expansion of thermoelectric (M,M’,M”)NiSn (M,M’,M”=Ti, Zr, Hf) half-Heusler alloys. Journal of Alloys and Compounds. ISSN 0925-8388. 959. doi: 10.1016/j.jallcom.2023.170583. Fulltekst i vitenarkiv
• Kanas, Nikola; Skomedal, Gunstein; Desissa, Temesgen D.; Feldhoff, Armin; Grande, Tor & Wiik, Kjell [Vis alle 7 forfattere av denne artikkelen] (2020). Performance of a thermoelectric module based on n-type (La0.12Sr0.88)0.95TiO3-δ and p-type Ca3Co4-xO9+δ . Journal of Electronic Materials. ISSN 0361-5235. 49(7), s. 4154–4159. doi: 10.1007/s11664-020-08127-5. Fulltekst i vitenarkiv Vis sammendrag

  Here, we present the performance of a thermoelectric (TE) module consisting of n-type (La0.12Sr0.88)0.95TiO3 and p-type Ca3Co4-xO9+δ materials. The main challenge in this investigation was operation of TE module in different atmosphere conditions, since n-type has its optimum TE-performance at reducing, while p-type at oxidizing conditions. The TE module was exposed to two different atmospheres and demonstrated higher stability in N2 atmosphere than in air. The maximum electrical power output decreased after 40 h when the hot side was exposed to N2 at 600 °C, while only 1 h at 400 °C in ambient air was enough to oxidize (La0.12Sr0.88)0.95TiO3 followed by a reduced electrical power output. The module generated a maximum electrical power of 0.9 mW (~ 4.7 mW/cm2) at 600 °C hot side and ΔT ~ 570 K in N2, while 0.15 mW (~ 0.8 mW/cm2) at 400 °C hot side and ΔT ~ 370 K in air. A stability limit of Ca3Co3.93O9+δ at ~ 700 °C in N2 was determined by in situ high-temperature X-ray diffraction.

• Kanas, Nikola; Bjørk, Rasmus; Wells, Kristin Høydalsvik; Schuler, Raphael; Einarsrud, Mari-Ann & Pryds, Nini [Vis alle 7 forfattere av denne artikkelen] (2020). Time-enhanced performance of oxide thermoelectric modules based on a hybrid p-n junction . ACS Omega. ISSN 2470-1343. 6(1), s. 197–205. doi: 10.1021/acsomega.0c04134. Fulltekst i vitenarkiv
• Gunnæs, Anette Eleonora; Tofan, Raluca; Berland, Kristian; Gorantla, Sandeep Madhukar; Storaas, Thomas Aarflot & Desissa, Temesgen Debelo [Vis alle 12 forfattere av denne artikkelen] (2020). Chemical stability of Ca3Co4−xO9+δ/CaMnO3−δ p–n junction for oxide-based thermoelectric generators. RSC Advances. ISSN 2046-2069. 10(9), s. 5026–5031. doi: 10.1039/c9ra07159h. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Schrade, Matthias; Berland, Kristian; Kosinskiy, Andrey; Heremans, Joseph P. & Finstad, Terje (2020). Shallow Impurity Band in ZrNiSn. Journal of Applied Physics. ISSN 0021-8979. 127(4). doi: 10.1063/1.5112820. Fulltekst i vitenarkiv Vis sammendrag

  ABSTRACT ZrNiSn and related half Heusler compounds are candidate materials for efficient thermoelectric energy conversion with a reported thermoelectric figure-of-merit of n-type ZrNiSn exceeding unity. Progress on p-type materials has been more limited, which has been attributed to the presence of an impurity band, possibly related to Ni interstitials in a nominally vacant 4d position. The specific energetic position of this band, however, has not been resolved. Here, we report the results of a concerted theory-experiment investigation for a nominally undoped ZrNiSn, based on the electrical resistivity, the Hall coefficient, the Seebeck coefficient, and the Nernst coefficient, measured in a temperature range from 80 to 420 K. The results are analyzed with a semianalytical model combining a density functional theory (DFT) description for ideal ZrNiSn, with a simple analytical correction for the impurity band. The model provides a good quantitative agreement with experiment, describing all salient features in the full temperature span for the Hall, conductivity, and Seebeck measurements, while also reproducing key trends in the Nernst results. This comparison pinpoints the impurity band edge to 40 meV below the conduction band edge, which agrees well with a separate DFT study of a supercell containing Ni interstitials. Moreover, we corroborate our result with a separate study of the ZrNiSn0.9Pb0.1 sample showing similar agreement with an impurity band edge shifted to 32 meV below the conduction band.

• Bittner, Michael; Kanas, Nikola; Hinterding, Richard; Steinbach, Frank; Groeneveld, Dennis & Wemhoff, Piotr [Vis alle 9 forfattere av denne artikkelen] (2019). Triple-phase ceramic 2D nanocomposite with enhanced thermoelectric properties. Journal of the European Ceramic Society. ISSN 0955-2219. 39(4), s. 1237–1244. doi: 10.1016/j.jeurceramsoc.2018.10.023. Fulltekst i vitenarkiv
• Bittner, Michael; Kanas, Nikola; Hinterding, Richard; Steinbach, Frank; Räthel, Jan & Schrade, Matthias [Vis alle 9 forfattere av denne artikkelen] (2019). A comprehensive study on improved power materials for high-temperature thermoelectric generators. Journal of Power Sources. ISSN 0378-7753. 410-411, s. 143–151. doi: 10.1016/j.jpowsour.2018.10.076. Fulltekst i vitenarkiv Vis sammendrag

  Dense Ca3Co4O9-NaxCoO2-Bi2Ca2Co2O9 (CCO-NCO-BCCO) nanocomposites were produced from sol-gel derived Ca2.25Na0.3Bi0.35Tb0.1Co4O9 powder by four methods: Hot-pressing (HP), spark plasma sintering (SPS) and pressureless sintering in air or O2 atmosphere. Nanocomposites from HP and SPS revealed nanosized grains and showed a thermoelectric power factor of 4.8 and 6.6 μW cm−1 K−2, respectively, at 1073 K in air. A dense 2D nanocomposite with structures on multiple length scales and enhanced thermoelectric properties was obtained from pressureless sintering in O2 atmosphere. The resulting 2D nanocomposite enabled the simultaneous increase in isothermal electrical conductivity σ and Seebeck coefficient α, and showed a thermoelectric power factor of 8.2 μW cm−1 K−2 at 1073 K in air. The impact of materials with enhanced electrical conductivity and power factor on the electrical power output of thermoelectric generators was verified in prototypes. A high electrical power output and power density of 22.7mW and 113.5mW cm−2, respectively, were obtained, when a hot-side temperature of 1073 K and a temperature difference of 251 K were applied. Different p- and n-type materials were used to verify the effect of the thermoelectric figure-of-merit zT and power factor on the performance of thermoelectric generators.

• Singh, Sathya Prakash; Kanas, Nikola; Desissa, Temesgen Debelo; Johnsson, Mats; Einarsrud, Mari-Ann & Norby, Truls Eivind [Vis alle 7 forfattere av denne artikkelen] (2019). Thermoelectric properties of A-site deficient La-doped SrTiO3 at 100–900 °C under reducing conditions. Journal of the European Ceramic Society. ISSN 0955-2219. 40(2), s. 401–407. doi: 10.1016/j.jeurceramsoc.2019.09.024. Fulltekst i vitenarkiv
• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Almeida Carvalho, Patricia; Berland, Kristian & Sørby, Magnus Helgerud [Vis alle 9 forfattere av denne artikkelen] (2019). Long- and short-range structures of Ti1-xHfxNi1.0/1.1Sn half-Heusler compounds and their electric transport properties. CrysteEngComm. ISSN 1466-8033. 21, s. 3330–3342. doi: 10.1039/c9ce00046a. Fulltekst i vitenarkiv
• Skomedal, Gunstein; Vehus, Tore; Kanas, Nikola; Singh, Sathya Prakash; Einarsrud, Mari-Ann & Wiik, Kjell [Vis alle 7 forfattere av denne artikkelen] (2019). Long term stability testing of oxide unicouple thermoelectric modules. Materials Today: Proceedings. ISSN 2214-7853. 8(2), s. 696–705. doi: 10.1016/j.matpr.2019.02.070. Fulltekst i vitenarkiv
• Kanas, Nikola; Singh, Sathya Prakash; Rotan, Magnus; Desissa, Temesgen Debelo; Grande, Tor & Wiik, Kjell [Vis alle 8 forfattere av denne artikkelen] (2019). Thermoelectric Properties of Ca3Co2−xMnxO6 (x = 0.05, 0.2, 0.5, 0.75, and 1). Materials. ISSN 1996-1944. 12(3). doi: 10.3390/ma12030497. Fulltekst i vitenarkiv Vis sammendrag

  High-temperature instability of the Ca3Co4−yO9+δ and CaMnO3−δ direct p-n junction causing the formation of Ca3Co2−xMnxO6 has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca3Co2−xMnxO6 with x = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca3CoMnO6 (x = 1) demonstrated a large positive Seebeck coefficient of 668 μV/K at 900 °C, but very low electrical conductivity. Materials with compositions with x < 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 ± 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1−x. The conductivity reached about 11 S·cm−1 at 900 °C for x = 0.05. The material Ca3Co1.8Mn0.2O6 (x = 0.2) yielded a maximum zT of 0.021 at 900 °C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca3Co2−xMnxO6 layers between Ca3Co4−yO9+δ and CaMnO3−δ open for new geometries and designs of oxide-based thermoelectric generators.

• Berland, Kristian; Shulumba, Nina; Hellman, Olle; Persson, Clas & Løvvik, Ole Martin (2019). Thermoelectric transport trends in group 4 half-Heusler alloys. Journal of Applied Physics. ISSN 0021-8979. 126(14), s. 1–15. doi: 10.1063/1.5117288. Fulltekst i vitenarkiv Vis sammendrag

  The thermoelectric properties of 54 different group 4 half-Heusler (HH) alloys have been studied from first principles. Electronic transport was studied with density functional theory using hybrid functionals facilitated by the k⋅p method, while the temperature-dependent effective potential method was used for the phonon contributions to the figure of merit ZT. The phonon thermal conductivity was calculated including anharmonic phonon-phonon, isotope, alloy, and grain-boundary scattering. HH alloys have an XYZ composition, and those studied here are in the group 4-9-15 (Ti,Zr,Hf)(Co,Rh,Ir)(As,Sb,Bi) and group 4-10-14 (Ti,Zr,Hf)(Ni,Pd,Pt)(Ge,Sn,Pb). The electronic part of the thermal conductivity was found to significantly impact ZT and thus the optimal doping level. Furthermore, the choice of functional was found to significantly affect thermoelectric properties, particularly for structures exhibiting band alignment features. The intrinsic thermal conductivity was significantly reduced when alloy and grain-boundary scattering were accounted for, which also reduced the spread in thermal conductivity. It was found that sublattice disorder on the Z-site, i.e., the site occupied by group 14 or 15 elements, was more effective than X-site substitution, occupied by group 4 elements. The calculations confirmed that ZrNiSn, ZrCoSb, and ZrCoBi based alloys display promising thermoelectric properties. A few other n-type and p-type compounds were also predicted to be potentially excellent thermoelectric materials, given that sufficiently high charge carrier concentrations can be achieved. This study provides insight into the thermoelectric potential of HH alloys and casts light on strategies to optimize the thermoelectric performance of multicomponent alloys.

• Desissa, Temesgen D.; Kanas, Nikola; Singh, Sathya Prakash; Wiik, Kjell; Einarsrud, Mari-Ann & Norby, Truls Eivind (2018). Chemical tracer diffusion of Sr and Co in polycrystalline Ca-deficient CaMnO3-δ with CaMn2O4 precipitates. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 20(4), s. 2754–2760. doi: 10.1039/c7cp07471a. Fulltekst i vitenarkiv Vis sammendrag

  Diffusivity on the A- and B-site of polycrystalline perovskite CaMnO3-δ with Ca deficiency and spinel CaMn2O4 (marokite) as a secondary phase was studied using chemical tracers and secondary ion mass spectrometry (SIMS) complemented by electron probe microanalysis (EPMA). Thin films containing Sr and Co chemical tracers were deposited on the polished surface of the polycrystalline composite sample followed by annealing at 800 – 1200 °C for 96 h. Diffusion profiles for each tracer were determined with SIMS, followed by calculation of diffusion coefficients by fitting to appropriate models. The Sr tracer showed mainly lattice diffusion, with an activation energy of 210±30 kJ/mol, whereas the Co tracer showed a combination of lattice and enhanced grain-boundary diffusion, with activation energies of 270±30 kJ/mol and 380±40 kJ/mol, respectively. The diffusivities may be used to predict interdiffusion and lifetime of junctions between n-type CaMnO3-δ or CaMnO3-δ/CaMn2O4 composites and metallization interlayers or p-type leg materials in oxide thermoelectrics. In particular, the relatively high effective diffusivity of Co in polycrystalline CaMnO3 δ may play a role in the reported fast formation of the secondary phase (Ca3Co2-yMnyO6) between p-type Ca3Co3.92O9+δ and n-type CaMnO3-δ in a direct p-n thermoelectric junction.

• Abu Hamed, Tareq; Adamovic, Nadja; Aeberhard, Urs; Alonso-Alvarez, Diego; Amin-Akhlaghi, Zoe & Auf der Maur, Matthias [Vis alle 82 forfattere av denne artikkelen] (2018). Multiscale in modelling and validation for solar photovoltaics. EPJ Photovoltaics. ISSN 2105-0716. 9. doi: 10.1051/epjpv/2018008.
• Kanas, Nikola; Bittner, Michael; Desissa, Temesgen Debelo; Singh, Sathya Prakash; Norby, Truls Eivind & Feldhoff, Armin [Vis alle 9 forfattere av denne artikkelen] (2018). All-Oxide Thermoelectric Module with in Situ Formed Non-Rectifying Complex p-p-n Junction and Transverse Thermoelectric Effect. ACS Omega. ISSN 2470-1343. 3(8), s. 9899–9906. doi: 10.1021/acsomega.8b01357. Fulltekst i vitenarkiv Vis sammendrag

  All-oxide thermoelectric modules for energy harvesting are attractive due to high temperature stability, low cost, and the potential to use non-scarce and non-toxic elements. Thermoelectric modules are mostly fabricated in the conventional π-design, associated with the challenge of unstable metallic interconnects at high temperature. Here, we report on a novel approach to fabrication of a thermoelectric module with an in situ formed p-p-n junction made of state-of-the-art oxides Ca3Co4-xO9+δ (p-type) and CaMnO3-CaMn2O4 composite (n-type). The module was fabricated by spark plasma co-sintering of p- and n-type powders partly separated by insulating LaAlO3. Where the n- and p-type materials originally were in contact, a layer of p-type Ca3CoMnO6 was formed in situ. The hence formed p-p-n junction exhibited ohmic behavior and a transverse thermoelectric effect, boosting the open circuit voltage of the module. The performance of the module was characterized at 700 - 900 °C, with the highest power output of 5.7 mW (around 23 mW/cm2) at 900 °C and a temperature difference of 160 K. The thermoelectric properties of the p- and n-type materials were measured in the temperature range 100 - 900 °C, where the highest zT of 0.39 and 0.05 were obtained at 700 and 800 °C, respectively, for Ca3Co4-xO9+δ and the CaMnO3-CaMn2O4 composite.

• Schrade, Matthias & Finstad, Terje (2018). Using the Callaway Model to Deduce Relevant Phonon Scattering Processes: The Importance of Phonon Dispersion. Physica status solidi (b). ISSN 0370-1972. 255(12), s. 1–6. doi: 10.1002/pssb.201800208.
• Desissa, Temesgen D.; Haugsrud, Reidar; Wiik, Kjell & Norby, Truls Eivind (2018). Inter-diffusion across a direct p-n heterojunction of Li-doped NiO and Al-doped ZnO. Solid State Ionics. ISSN 0167-2738. 320, s. 215–220. doi: 10.1016/j.ssi.2018.03.011. Fulltekst i vitenarkiv Vis sammendrag

  We herein report inter-diffusion across the interface between p-type Ni0.98Li0.02O and n-type Zn0.98Al0.02O for various applications including p-n-heterojunction diodes and oxide thermoelectrics. Diffusion couples were made of polished surfaces of ceramic samples pre-sintered at 1250 and 1350 °C for Ni0.98Li0.02O and Zn0.98Al0.02O, respectively. The inter-diffusion couples were annealed at 900–1200 °C for 160 h in ambient air. Electron Probe Micro Analysis (EPMA) was used to acquire diffusion profiles, followed by fitting to Fick's second law and Whipple–Le Claire's models for bulk and grain-boundary diffusion calculation, respectively. Zn2+ diffused into Ni0.98Li0.02O mainly by bulk diffusion with an activation energy of 250 ± 10 kJ/mol, whereas Ni2+ diffused into Zn0.98Al0.02O by both bulk and enhanced grain boundary diffusion with activation energies of 320 ± 120 kJ/mol and 245 ± 50 kJ/mol, respectively. The amount of Al3+ diffused from the Al-doped ZnO into the NiO phase was too small for a corresponding diffusion coefficient to be calculated. Li-ion distribution and diffusivity were not determined due to lack of analyzer sensitivity for Li. The bulk and effective diffusivities of Zn2+ and Ni2+ into NiO and ZnO enable prediction of inter-diffusion lengths as a function of time and temperature, allowing estimates of device performance, stability, and lifetimes at different operation temperatures.

• Guzik, Matylda N.; Echevarria-Bonet, Cristina; Riktor, Marit Dalseth; Almeida Carvalho, Patricia; Gunnæs, Anette Eleonora & Sørby, Magnus Helgerud [Vis alle 7 forfattere av denne artikkelen] (2018). Half-Heusler phase formation and Ni atom distribution in M-Ni-Sn (M = Hf, Ti, Zr) systems. Acta Materialia. ISSN 1359-6454. 148, s. 216–224. doi: 10.1016/j.actamat.2018.01.019. Fulltekst i vitenarkiv
• Hansen, Vidar; Echevarria-Bonet, Cristina; Minde, Mona Wetrhus & Taftø, Johan (2018). Determination of atomic positions and polar direction in half-Heusler material Sb1- xSnxTi1-y-zHfyZrzCo using electron channeling. AIP Advances. ISSN 2158-3226. 8(12), s. 1–9. doi: 10.1063/1.5042816. Fulltekst i vitenarkiv
• Musland, Lars & Flage-Larsen, Espen (2018). Thermoelectric effect in superlattices; applicability of coherent and incoherent transport models. Computational Materials Science. ISSN 0927-0256. 153, s. 88–96. doi: 10.1016/j.commatsci.2018.05.044. Fulltekst i vitenarkiv
• Berland, Kristian & Persson, Clas (2018). Thermoelectric transport of GaAs, InP, and PbTe: Hybrid functional with kp interpolation versus scissor-corrected generalized gradient approximation. Journal of Applied Physics. ISSN 0021-8979. 123. doi: 10.1063/1.5030395. Fulltekst i vitenarkiv
• Kanas, Nikola; Singh, Sathya Prakash; Rotan, Magnus; Saleemi, Mohsin; Bittner, Michael & Feldhoff, Armin [Vis alle 10 forfattere av denne artikkelen] (2018). Influence of processing on stability, microstructure and thermoelectric properties of Ca3Co4-xO9+δ. Journal of the European Ceramic Society. ISSN 0955-2219. 38(4), s. 1592–1599. doi: 10.1016/j.jeurceramsoc.2017.11.011. Fulltekst i vitenarkiv Vis sammendrag

  Due to high figure of merit, Ca3Co4-xO9+δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 °C for CCO with 98 and 72 % relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen ( ̴ 970 °C) than in air ( ̴ 930 °C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 °C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.

• Zamulko, Sergii; Berland, Kristian & Persson, Clas (2018). Optical properties of Cu2ZnSn(S(x)Se(1-x))4 by first-principles calculations. Physica Status Solidi (a) applications and materials science. ISSN 1862-6300. 215(17), s. 1–7. doi: 10.1002/pssa.201700945. Fulltekst i vitenarkiv
• Desissa, Temesgen D.; Schrade, Matthias & Norby, Truls Eivind (2018). Electrical Properties of a p–n Heterojunction of Li-Doped NiO and Al-Doped ZnO for Thermoelectrics. Journal of Electronic Materials. ISSN 0361-5235. 47(9), s. 5296–5301. doi: 10.1007/s11664-018-6394-3. Fulltekst i vitenarkiv Vis sammendrag

  The electrical properties of a p–n heterojunction of polycrystalline p-type Ni0.98Li0.02O and n-type Zn0.98Al0.02O have been investigated for potential applications in high-temperature oxide-based thermoelectric generators without metallic interconnects. Current–voltage characteristics of the junction were measured in a two-electrode setup in ambient air at 500–1000°C. The resistance and rectification of the junction decreased with increasing temperature. A non-ideal Shockley diode model was used to fit the measured current–voltage data in order to extract characteristic parameters of the junction, such as area specific series resistance Rs and parallel shunt resistance Rp, non-ideality factor, and the saturation current density. Rs and Rp decreased exponentially with temperature, with activation energies of 0.4 ± 0.1 eV and 1.1 ± 0.2 eV, respectively. The interface resistance of the direct p–n junction studied here is as such too high for practical applications in thermoelectrics. However, it is demonstrated that it can be reduced by an order of magnitude by using a composite of the individual materials at the interface, yielding a large effective contact area.

• Eliassen, Simen Nut Hansen; Katre, Anikta; Madsen, Georg; Persson, Clas; Løvvik, Ole Martin & Berland, Kristian (2017). Lattice thermal conductivity of TixZryHf1−x−yNiSn half-Heusler alloys calculated from first principles: Key role of nature of phonon modes. Physical review B (PRB). ISSN 2469-9950. 95(4). doi: 10.1103/PhysRevB.95.045202. Fulltekst i vitenarkiv Vis sammendrag

  In spite of their relatively high lattice thermal conductivity κℓ, the XNiSn (X=Ti, Zr, or Hf) half-Heusler compounds are good thermoelectric materials. Previous studies have shown that κℓ can be reduced by sublattice alloying on the X site. To cast light on how the alloy composition affects κℓ, we study this system using the phonon Boltzmann-transport equation within the relaxation time approximation in conjunction with density functional theory. The effect of alloying through mass-disorder scattering is explored using the virtual crystal approximation to screen the entire ternary TixZryHf1−x−yNiSn phase diagram. The lowest lattice thermal conductivity is found for the TixHf1−xNiSn compositions; in particular, there is a shallow minimum centered at Ti0.5Hf0.5NiSn with κℓ taking values between 3.2 and 4.1 W/mK when the Ti content varies between 20% and 80%. Interestingly, the overall behavior of mass-disorder scattering in this system can only be understood from a combination of the nature of the phonon modes and the magnitude of the mass variance. Mass-disorder scattering is not effective at scattering acoustic phonons of low energy. By using a simple model of grain boundary scattering, we find that nanostructuring these compounds can scatter such phonons effectively and thus further reduce the lattice thermal conductivity; for instance, Ti0.5Hf0.5NiSn with a grain size of L=100 nm experiences a 42% reduction of κℓ compared to that of the single crystal.

• Vøllestad, Einar; Schrade, Matthias; Segalini, Julie; Strandbakke, Ragnar & Norby, Truls Eivind (2017). Relating defect chemistry and electronic transport in the double perovskite Ba1-xGd0.8La0.2+xCo2O6-d (BGLC). Journal of Materials Chemistry A. ISSN 2050-7488. 5(30), s. 15743–15751. doi: 10.1039/c7ta02659e. Fulltekst i vitenarkiv
• Berland, Kristian; Jiao, Yiao; Lee, Jung-Hoon; Rangel, Tonatiuh; Neaton, Jeffrey B. & Hyldgaard, Per (2017). Assessment of two hybrid van der Waals density functionals for covalent and non-covalent binding of molecules. Journal of Chemical Physics. ISSN 0021-9606. 146(23). doi: 10.1063/1.4986522. Fulltekst i vitenarkiv
• Schrade, Matthias; Maso Carcases, Nahum; Perejón, Antonio; Pérez-Maqueda, Luis A. & West, Anthony R. (2017). Defect chemistry and electrical properties of BiFeO3. Journal of Materials Chemistry C. ISSN 2050-7526. 5(38), s. 10077–10086. doi: 10.1039/c7tc03345a.
• Song, Xin & Finstad, Terje (2017). A study of S doped ZnSb. Materials Science in Semiconductor Processing. ISSN 1369-8001. 71, s. 421–426. doi: 10.1016/j.mssp.2017.09.007. Vis sammendrag

  We report on S-doping of ZnSb for S concentrations ranging from 0.02 at% to 2.5 at%. There are no previous reports on S-doping. ZnSb is a thermoelectric material with some advantages for the temperature range 400 K - 600 K. The solid solubility of S in ZnSb was estimated to be lower than 0.1% from observations of precipitates by scanning microscopy. Hall and Seebeck measurements were performed as a function of temperature from 6K to 623 K. The temperature dependence of the electrical properties suggests that S introduces neutral scattering centers for holes in the p-type material. An increase in hole concentration by S is argued by defect reactions involving Zn vacancies.

• Cerretti, G; Schrade, Matthias; Song, Xin; Balke, B; Lu, H & Weidner, T [Vis alle 10 forfattere av denne artikkelen] (2017). Thermal stability and enhanced thermoelectric properties of the tetragonal tungsten bronzes Nb8-xW9+xO47 (0 < x < 5). Journal of Materials Chemistry A. ISSN 2050-7488. 5(20), s. 9768–9774. doi: 10.1039/c7ta01121k.
• Song, Xin; Schrade, Matthias; Maso Carcases, Nahum & Finstad, Terje (2017). Zn vacancy formation, Zn evaporation and decomposition of ZnSb at elevated temperatures: Influence on the microstructure and the electrical properties. Journal of Alloys and Compounds. ISSN 0925-8388. 710, s. 762–770. doi: 10.1016/j.jallcom.2017.03.339. Fulltekst i vitenarkiv Vis sammendrag

  The influence of annealing on the microstructure and electrical properties of undoped polycrystalline ZnSb samples has been investigated by different experimental techniques. In situ XRD in an argon at- mosphere showed that ZnSb powders decompose at 300 C, which is attributed to Zn evaporation. In situ SEM in a moist atmosphere showed fast surface deterioration at 450 C and above, reflecting decom- position of ZnSb and the formation of metallic Sb precipitates. The rate of Zn loss in a reducing atmo- sphere was determined by thermogravimetry and related to the Zn partial vapor pressure. The increase of the hole carrier concentration of ZnSb measured at room temperature after heat treatment was correlated with Zn evaporation at elevated temperature. The carrier concentration after annealing at 400 C is consistent with an activation energy for Zn vacancy formation of 0.4 eV and a maximum Zn deficiency x of Zn1-xSb of 1 10 3.

• Berland, Kristian & Persson, Clas (2017). Enabling accurate first-principle calculations of electronic properties with a corrected kp scheme. Computational Materials Science. ISSN 0927-0256. 134, s. 17–24. doi: 10.1016/j.commatsci.2017.03.017.
• Schrade, Matthias; Berland, Kristian; Eliassen, Simen Nut Hansen; Guzik, Matylda Natalia; Echevarria-Bonet, Cristina & Sørby, Magnus Helgerud [Vis alle 13 forfattere av denne artikkelen] (2017). The role of grain boundary scattering in reducing the thermal conductivity of polycrystalline XNiSn (X=Hf, Zr, Ti) half-Heusler alloys. Scientific Reports. ISSN 2045-2322. 7. doi: 10.1038/s41598-017-14013-8. Fulltekst i vitenarkiv
• Berland, Kristian; Song, Xin; Carvalho, Patricia; Persson, Clas; Finstad, Terje & Løvvik, Ole Martin (2016). Enhancement of thermoelectric properties by energy filtering: Theoretical potential and experimental reality in nanostructured ZnSb. Journal of Applied Physics. ISSN 0021-8979. 119(12). doi: 10.1063/1.4944716. Fulltekst i vitenarkiv Vis sammendrag

  Energy filtering has been suggested by many authors as a means to improve thermoelectric properties. The idea is to filter away low-energy charge carriers in order to increase Seebeck coefficient without compromising electronic conductivity. This concept was investigated in the present paper for a specific material (ZnSb) by a combination of first-principles atomic-scale calculations, Boltzmann transport theory, and experimental studies of the same system. The potential of filtering in this material was first quantified, and it was as an example found that the power factor could be enhanced by an order of magnitude when the filter barrier height was 0.5 eV. Measured values of the Hall carrier concentration in bulk ZnSb were then used to calibrate the transport calculations, and nanostructured ZnSb with average grain size around 70 nm was processed to achieve filtering as suggested previously in the literature. Various scattering mechanisms were employed in the transport calculations and compared with the measured transport properties in nanostructured ZnSb as a function of temperature. Reasonable correspondence between theory and experiment could be achieved when a combination of constant lifetime scattering and energy filtering with a 0.25 eV barrier was employed. However, the difference between bulk and nanostructured samples was not sufficient to justify the introduction of an energy filtering mechanism. The reasons for this and possibilities to achieve filtering were discussed in the paper.

• Kosinskiy, Andrey; Karlsen, Ole Bjørn; Sørby, Magnus Helgerud & Prytz, Øystein (2016). Ternary Phases (Heusler) in the System Ti-Co-Sn. Metallurgical and Materials Transactions E. ISSN 2196-2936. 3(4), s. 329–336. doi: 10.1007/s40553-016-0098-5. Fulltekst i vitenarkiv
• Bittner, Michael; Geppert, Benjamin; Kanas, Nikola; Singh, Sathya Prakash; Wiik, Kjell & Feldhoff, Armin (2016). Oxide-Based Thermoelectric Generator for High-Temperature Application Using p-Type Ca3Co4O9 and n-Type In1.95Sn0.05O3 Legs. Energy Harvesting and Systems. ISSN 2329-8774. 3(3), s. 213–222. doi: 10.1515/ehs-2016-0002.

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• Berland, Kristian; Eliassen, Simen Nut Hansen; Løvvik, Ole Martin; Persson, Clas & Schrade, Matthias (2018). Computational Engineering of Thermoelectric Materials.
• Vehus, Tore; Skomedal, Gunstein; Kanas, Nikola & Middleton, Peter Hugh (2018). Hot side electrical contacts for oxide thermoelectric modules.
• Wiik, Kjell; Singh, Sathya Prakash; Kanas, Nikola & Einarsrud, Mari-Ann (2018). All-oxide thermoelectric generators and the development of n-type oxides with improved thermoelectric properties.
• Wiik, Kjell; Singh, Sathya Prakash; Kanas, Nikola & Einarsrud, Mari-Ann (2018). All-oxide thermoelectrics for high temperature applications-Materials and devices.
• Berland, Kristian; Zamulko, Sergii & Persson, Clas (2017). Resolving fine features of the dielectric function: Computational issues and opportunities.
• Berland, Kristian; Zamulko, Sergii & Persson, Clas (2017). Comparison of hybrid functional and GGA for transport and excited-state properties of bulk semiconductors.
• Schrade, Matthias (2017). Nye materialer lager strøm av temperaturforskjeller. Apollon : Forskningsmagasin for Universitetet i Oslo. ISSN 0803-6926. 27(1), s. 26–29.
• Schrade, Matthias; Berland, Kristian; Guzik, Matylda Natalia; Løvvik, Ole Martin & Finstad, Terje (2017). Why does the thermal conductivity of XNiSn vary for nominally identical samples?
• Persson, Clas (2017). Tailor-making materials for 100-nm thin inorganic solar cells.
• Løvvik, Ole Martin (2017). Californias miljøkamp inspirerer. [Radio]. Intervju i Ekko, NRK P2.
• Løvvik, Ole Martin (2017). Hva skjer hvis du setter et kjøleskap i fryseren? [Radio]. Intervju i Ekko, NRK P2.
• Løvvik, Ole Martin; Shulumba, Nina; Hellman, Olle; Persson, Clas & Berland, Kristian (2017). Predicted figure-of-merit of half-Heusler alloys - importance of scattering mechanisms.
• Singh, Sathya Prakash; Kanas, Nikola; Norby, Truls Eivind; Johnsson, Mats; Einarsrud, Mari-Ann & Wiik, Kjell (2017). Thermoelectric properties of (La0.12Sr0.88)0.95TiO3 between 100 and 900 oC at reducing conditions.
• Berland, Kristian; Eliassen, Simen Nut Hansen; Schrade, Matthias; Tofan, Raluca; Guzik, Matylda Natalia & Gunnæs, Anette Eleonora [Vis alle 11 forfattere av denne artikkelen] (2017). Using theory to understand thermoelectric materials.
• Berland, Kristian & Persson, Clas (2017). The need for dense Brillouin zone sampling in transport and optical calculations... and how to deal with it.
• Berland, Kristian; Løvvik, Ole Martin & Persson, Clas (2017). How hybrid exchange affects thermoelectric transport properties of GaAs, PbTe, Cu2Se, and half Heuslers: Accurate grid sampling enabled with a corrected k.p scheme.
• Berland, Kristian & Persson, Clas (2017). Computing accurate dielectric functions and transport properties of semiconductors with help of a new k.p based interpolation scheme.
• Desissa, Temesgen D. & Norby, Truls Eivind (2017). Electrical properties and diffusion coefficient analysis of NiO:Li/ZnO:Al p-n heterojunction for oxide based thermoelectric generators.
• Guzik, Matylda N.; Schrade, Matthias; Tofan, Raluca; Berland, Kristian; Gunnæs, Anette Eleonora & Persson, Clas [Vis alle 8 forfattere av denne artikkelen] (2017). Structural Investigation of Ti1-xHfxNiySn Half-Heusler Compounds.
• Guzik, Matylda N.; Echevarria-Bonet, Cristina; Sørby, Magnus Helgerud & Hauback, Bjørn (2017). Half-Heusler Phase Formation and Ni atom distribution in M-Ni-Sn (M = Hf, Ti, Zr) System.
• Skomedal, Gunstein (2017). Long term stability testing of oxide unicouple thermoelectric modules.
• Berland, Kristian; Eliassen, Simen Nut Hansen; Katre, Anikta; Madsen, Georg; Persson, Clas & Løvvik, Ole Martin (2016). How to bring down the thermal conductivity of MNiSn Half-Heuslers - a theoretical analysis .
• Løvvik, Ole Martin; Eliassen, Simen Nut Hansen; Berland, Kristian & Peters, Thijs (2016). Transport properties of functional materials – understanding the motion of electrons, atoms, and phonons.
• Løvvik, Ole Martin; Eliassen, Simen Nut Hansen; Berland, Kristian & Peters, Thijs (2016). Transport in materials – understanding the motion of electrons, atoms, and phonons.
• Løvvik, Ole Martin; Eliassen, Simen Nut Hansen & Berland, Kristian (2016). Transport calculations of thermoelectric materials from first principles.
• Berland, Kristian; Persson, Clas & Tomic, Stanko (2016). STSM Report: Connecting the ab initio atomistic with continuum modeling: parameterization.
• Schrade, Matthias (2016). Å hente strøm fra varme overflater kan bli like vanlig som å hente strøm fra sollys. [Internett]. Teknisk Ukeblad.
• Schrade, Matthias (2016). 900 deltok på festival. [TV]. NRK.
• Løvvik, Ole Martin; Shulumba, Nina & Hellman, Olle (2016). Thermal conductivity from the temperature dependent effective potential (TDEP) method.
• Desissa, Temesgen D. & Norby, Truls (2016). A p-Ni1-xLixO and n-Zn1-xAlxO p-n junctions for oxide-based thermoelectric modules. Vis sammendrag

  A p-type Ni0.98Li0.02O and n-type Zn0.98Al0.02O thermoelectric materials have been synthesized from their respective powder precursors via solid state synthesis technique from which a pellets were obtained by uniaxial pressing. The pellets were sintered at a sintering temperature of 1523 K and 1623 K for Ni0.98Li0.02O and Zn0.98Al0.02O, respectively. The sintered samples were carefully polished to a surface finish of ¼ μm by using a diamond abrasive before establishing a p-n junction. After a p-n junction is formed, an I-V and C-V measurement has been performed. The p-n junction is rectifying in the lower temperature region and became ohmic in the highest temperature. A p-n junction resistivity was delineated from the overall resistivity and it constituted the main part of the overall resistivity. A built-in voltage of 0.875± 0.039 V was obtained from a C-V measurement at a frequency of 1 MHz at a temperature of 1173 K. Additionally, the p-n junction was annealed in ambient air at 1173 K for 160 hours to determine inter-diffusion coefficient using an electron probe micro analyzer (EPMA). The bulk diffusion coefficient of Ni2+ and Zn2+ was about 4.08*10-15 cm2/s and 4.51 * 10-15 cm2/s, respectively, after fitting to the solution of Fick’s second law of diffusion equation with a semi-infinite source type.

• Musland, Lars (2016). BTE and Landauer results for crossplane transport in superlattices.
• Singh, Sathya Prakash; Einarsrud, Mari-Ann & Wiik, Kjell (2016). Thermoelectric properties of Ta doped CaMnO3.
• Guzik, Matylda Natalia (2016). Influence of Phase Composition and Microstructure on Thermoelectric Properties of Half‐Heuslers.
• Berland, Kristian & Persson, Clas (2016). A corrected k.p scheme for accurate electronic properties .
• Berland, Kristian; Eliassen, Simen Nut Hansen; Katre, A; Madsen, Georg; Løvvik, Ole Martin & Persson, Clas (2016). Optimizing the thermoelectric properties of (TiHfZr)NiSn alloys.
• Kanas, Nikola (2016). Ceramic processing of all‐oxide ceramic thermoelectric module.
• Røe, Ingeborg Treu (2016). Simulation of Phonon Propagation in Thermoelectric Materials.
• Norby, Truls (2016). Protonics og termoelektrisitet.
• Schrade, Matthias; Echevarria-Bonet, Cristina; Eliassen, Simen Nut Hansen; Berland, Kristian; Persson, Clas & Tofan, Raluca [Vis alle 9 forfattere av denne artikkelen] (2016). Thermal Properties of XNiSn(X = Hf, Zr, Ti) half Heusler Alloys.
• Schrade, Matthias; Echevarria-Bonet, Cristina; Guzik, Matylda Natalia; Tofan, Raluca; Gunnæs, Anette Eleonora & Eliassen, Simen Nut Hansen [Vis alle 10 forfattere av denne artikkelen] (2016). Thermal properties of XNiSN (X = Ti, Zr, Hf) half Heusler alloys.
• Berland, Kristian & Persson, Clas (2016). Enabling accurate transport calculations with a k.p-method based interpolation scheme: Applications to thermoelectric properties.
• Løvvik, Ole Martin (2016). Måling av varmeledning med lasere på Caltech. [Radio]. Intervju i Ekko, NRK P2.
• Løvvik, Ole Martin (2016). Denne bilen går på telys - kan drive frem ny utvikling. Aftenposten Viten. ISSN 2464-3033.
• Sørby, Magnus Helgerud; Heere, Michael; Frommen, Christoph & Hauback, Bjørn (2016). Rare-earth borohydrides - crystal structures and in-situ characterization.
• Echevarria-Bonet, Cristina; Guzik, Matylda Natalia; Sørby, Magnus Helgerud & Hauback, Bjørn (2016). Composition of n-type Half-Heusler Compounds by SR-PXD .
• Tofan, Raluca; Echevarria-Bonet, Cristina; Berland, Kristian; Schrade, Matthias; Sørby, Magnus Helgerud & Hauback, Bjørn Christian [Vis alle 10 forfattere av denne artikkelen] (2016). Microstructural characterization of spark plasma sintered (X,X’)NiSn half‐Heusler alloys.
• Skomedal, Gunstein (2016). Denne bilen går på telys. [Tidsskrift]. Aftenposten Viten.
• Skomedal, Gunstein (2016). HAN SKAL FINNE OPP NYE MÅTER Å LAGE STRØM PÅ. [Avis]. Fedrelandsvennen.
• Skomedal, Gunstein (2016). Thermally activated degradation processes in thermoelectric materials and devices based on Skutterudites and Silicides.
• Wiik, Kjell (2015). Oxide Thermoelectric materials.
• Kanas, Nikola (2015). Ceramic processing of all-oxide ceramic thermoelectric module.
• Løvvik, Ole Martin (2015). Termoelektrisitet kan lage strøm fra spillvarme. [Radio]. Intervju i Jacobsen, NRK P1+.
• Løvvik, Ole Martin (2015). Transport plans for Caltech.
• Eliassen, Simen Nut Hansen; Berland, Kristian & Løvvik, Ole Martin (2015). FIRST PRINCIPLE CALCULATIONS OF THERMAL CONDUCTIVITY IN HALF-HEUSLER COMPOUNDS.
• Desissa, Temesgen D.; Norby, Truls Eivind & Haugsrud, Reidar (2018). Stability and properties of materials and interfaces for oxide thermoelectrics. Universistetet i Oslo. ISSN 1501-7710. 2018(1969).
• Singh, Sathya Prakash & Wiik, Kjell (2018). Development of oxides with n-type electronic conductivity for applications in high temperature thermoelectric generators (TEGs). NTNU. ISSN 978-82-326-3544-3. 2018(378).
• Prytz, Øystein; Flage-Larsen, Espen & Bilden, Sindre Rannem (2018). Simulation of momentum resolved Electron Energy Loss Spectroscopy in the low loss region using model band structures. Unipub forlag. Vis sammendrag

  One of the key limiting factors to progress within nano science is the ability to measure properties on the relevant length scale. The probe size provided by optical measurements is often larger than the individual nanoscale structures, and the resulting measurement is an average over some large volume, thus other methods must be applied. Electron Energy Loss Spectroscopy (EELS) in a Transmission Electron Microscope (TEM) provides a probe size suitable for measuring on nanoscopic structures, but the physics of the probe change when using electrons instead of photons. The fast electrons passing through the sample carry a significant momentum in addition to energy, and both can be transferred to an electron in the sample. The possible transfer of momentum in addition to energy increases the number of possible excitations immensely thus making the spectra of EELS more complex than its optical equivalent. The EELS-spectra also provide useful information about properties earlier methods could not measure such as excitations resolved by momentum, and a straight measure of transitions across indirect band gaps. However, simulations are key in interpretation of EELS where transitions with momentum transfer contribute. Most simulation software for EELS focus on the optical limit and a production ready software for momentum resolved simulations is so far missing. In the present project a simulation software for EELS is developed for a momentum and energy resolved spectrum. Based on existing theory, a full framework for EELS simulation is developed in the dielectric formulation, strongly depending on the dielectric permittivity. The framework has been implemented with focus on a interactive visualization and interpretation of the result which should be easy to handle. Some limitations have been encountered when it comes to computational cost when mapping both momentum and energy. To limit the computational cost, the permittivity was heavily simplified by treating only its longitudinal component. When applying the software on parabolic bands it was found that the calculated joint density of states reproduced analytically derived results. In calculations of joint density of states of parabolic bands with indirect band gap it was found that the intensity onset had different shape when probing a range of momentum transfers opposed to single momentum transfers. When applied to electronic structure models from tight binding calculations, it was found that the longitudinal permittivity was not sufficient to describe the full response of the systems. The longitudinal permittivity is found insufficient in the presence of transverse electric fields and in non-isotropic systems, thus a correction to the permittivity has been presented, this has not been implemented. To conclude, the developed software indicates that momentum resolved calculations can provide useful information in its simplest manner, and be comparable to experiment with further development.

• Salim Asbah, Richard; Flage-Larsen, Espen & Prytz, Øystein (2018). Quadratic integration over the three dimensional Brillouin zone. Unipub forlag.
• Musland, Lars; Flage-Larsen, Espen; Prytz, Øystein & Bergli, Joakim (2018). Charge carrier transport in multilayered structures; thermoelectric applications. Unipub forlag.
• Ledezma, Katinka Ervig & Wiik, Kjell (2017). The relation between microstructure and thermoelectric properties in Ta-substituted A-site deficient CaMnO3. NTNU.
• Røe, Ingeborg Treu; Selbach, Sverre Magnus & Løvvik, Ole Martin (2017). Finite temperature ab initio simulations of the lattice thermal conductivity of XNiBi, X=(Sc, Y, La), based half-Heuslers. NTNU.
• Kolobekken, Sara Hizon & Einarsrud, Mari-Ann (2017). All oxide thermoelectric device based on Ca0.931Mn0.98Ta0.002O3-d-Ca3Co4O9 pn-junction. NTNU.
• 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. Vis sammendrag

  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).

• Eliassen, Simen Nut Hansen; Berland, Kristian & Løvvik, Ole Martin (2016). A first principles study of lattice thermal conductivity in XNiSn (X = Ti, Zr, Hf) half-Heusler alloys for thermoelectric applications. UiP.

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