Kamil Ciesielski - Academia.edu (original) (raw)

Papers by Kamil Ciesielski

Research paper thumbnail of Thermoelectric properties of (DyNiSn) 1−x (DyNiSb) x composite

Physica B: Condensed Matter, 2018

High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNi... more High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNiSb) x composite materials have been studied. For bulk pure DyNiSn and DyNiSb samples the Seebeck coefficient reaches-5.5 V/K at 480 K and 120 V/K at 540 K, respectively. Composite materials show metallic-like electrical resistivity and positive sign of Seebeck coefficient with values up to 50 times higher than in pure DyNiSn compound at 1000 K. Only for the sample with x = 0.47, the ball-milling drives to increase of Seebeck coefficient of about 37% at 650 K.

Research paper thumbnail of Magnetocaloric Effect in Antiferromagnetic Half-Heusler Alloy DyNiSb

Acta Physica Polonica A, 2018

The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound ... more The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound DyNiSb were studied on polycrystalline samples. The temperature variations of the magnetization and the heat capacity revealed a phase transition from paramagnetic to antiferromagnetic state at the Néel temperature TN 3.1 K. The compound exhibits normal and inverse magnetocaloric effect with the isothermal magnetic entropy change reaching 5.2 J/(kg K) at 4.8 K for a magnetic field change of 3 T. The estimated refrigerant capacity is about 58 J/kg.

Research paper thumbnail of Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations

Journal of Alloys and Compounds, 2018

Research paper thumbnail of Anomalous electronic properties in layered, disordered ZnVSb

Physical Review Materials, 2021

New materials discovery is the driving force for progress in solid state physics and chemistry. H... more New materials discovery is the driving force for progress in solid state physics and chemistry. Here we solve the crystal structure and comprehensively study physical properties of ZnVSb in the polycrystalline form. Synchrotron x-ray diffraction reveals that the compound attains a layered ZrSiS-type structure ($P4$/nmm, aaa = 4.09021(2) \AA{}, ccc = 6.42027(4) \AA{}). The unit cell is composed of a 2D vanadium network separated by Zn-Sb blocks that are slightly distorted from the ideal cubic arrangement. A considerable amount of vacancies were observed on the vanadium and antimony positions; the experimental composition is mathrmZnV0.91mathrmSb0.96{\mathrm{ZnV}}_{0.91}{\mathrm{Sb}}_{0.96}mathrmZnV0.91mathrmSb0.96. Low-temperature x-ray diffraction shows very subtle discontinuity in the lattice parameters around 175 K. Bonding V-V distance is below the critical separation of 2.97 \AA{} known from the literature, which allows for V-V orbital overlap and subsequent metallic conductivity. From ab initio calculations, we found that Zn...

Research paper thumbnail of Origin of the negative temperature coefficient of resistivity in the half-Heusler antimonides LuNiSb and YPdSb

Physical Review B, 2021

The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperatur... more The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperature range 2-300 K. For both compounds, the electrical resistivity was found to decrease with increasing temperature, showing a linear-in-T behavior over an extended temperature interval. In order to interpret the experimental data, a two-channel conductivity model was applied, which revealed that not only the semiconducting-like transport but also the metallic-like one exhibit negative temperature coefficients. The unusual behavior in the metallic channel was described within the Cote-Meisel formalism based on the diffraction model of strongly disordered metals. In addition, a weak localization scenario was considered including spin-orbit scattering and Coulomb interaction between conducting electrons. The electron-electron interaction was found most important at the lowest temperatures, where the semiconducting channel becomes ineffective, reminiscent of charge transport confined to a narrow yet finite-size metallic band located inside the semiconducting energy gap. The low-temperature resistivity of YPdSb appeared fully describable in terms of the Altshuler-Aronov quantum correction due to interacting electrons. In turn, the electronic transport in LuNiSb was found affected by the Kondo effect associated with a small amount of paramagnetic impurities present in the specimen investigated. The approach developed for LuNiSb and YPdSb can be applied to other half-Heusler compounds that exhibit atom disorder in their crystal structures.

Research paper thumbnail of Structural, thermodynamic and magnetotransport properties of half-Heusler compound HoPtSb

Journal of Alloys and Compounds, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Electronic properties of La TE 2 Ge 2 ( TE  = Fe, Co, Ni, Cu and Ru)

Solid State Communications, 2018

Abstract Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of... more Abstract Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray diffraction, magnetization and electrical resistivity measurements performed down to 2 K, supplemented by fully relativistic band structure and Fermi surface calculations. Results of the theoretical investigations of all the compounds are in line with the experimental findings, namely they show decreasing influence of 3d-electrons of the Fe, Co, Ni and Cu atoms on the electronic properties with increasing the atomic mass. In the case of LaFe2Ge2 the electrical resistivity measurements strongly suggest presence of spin fluctuations, which make that system very similar to the unconventional superconductor YFe2Ge2.

Research paper thumbnail of High-temperature power factor of half-Heusler phases RENiSb (RE = Sc, Dy, Ho, Er, Tm, Lu)

Journal of Alloys and Compounds, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Effect of secondary LuNiSn phase on thermoelectric properties of half-Heusler alloy LuNiSb

Materials Today: Proceedings, 2019

We report on the high-temperature (350 K <T< 1000 K) thermoelectric properties of the ternary com... more We report on the high-temperature (350 K <T< 1000 K) thermoelectric properties of the ternary compounds LuNiSb (cubic) and LuNiSn (orthorhombic) and a composite material (LuNiSb)0.5(LuNiSn)0.5. The electrical conductivity in LuNiSn is metallic, while it is semiconducting-like in LuNiSb. The Seebeck coefficient reaches-5.5 µV/K at 700 K for the former compound and 66 µV/K at 607 K for the latter one. The composite sample (LuNiSb)0.5(LuNiSn)0.5 constructed from orthorhombic matrix with cubic inclusions combines the electrical conductivity of LuNiSn with the thermoelectric properties of LuNiSb. Nonetheless, no enhancement of the thermoelectric performance occurs for this material.

Research paper thumbnail of High-temperature thermoelectric properties of half-Heusler phases Er1-xHoxNiSb

Materials Today: Proceedings, 2019

Polycrystalline samples of Er1-xHoxNiSb (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by... more Polycrystalline samples of Er1-xHoxNiSb (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and optical metallography. The results proved the formation of half-Heusler alloys in the entire composition range. Their electrical transport properties (resistivity, thermoelectric power) were studied in the temperature interval 350-1000 K. The measured electrical resistivity spanned between 5 and 25 m. The maximum thermopower of 50-65 V/K was observed at temperatures 500-650 K. Replacing Ho for Er resulted in a non-monotonous variation of the thermoelectric power factor (PF = S 2 /). The largest PF of 4.6 WcmK-2 was found at 660 K for Er0.5Ho0.5NiSb. This value is distinctly larger than PF determined for the terminal phases ErNiSb and HoNiSb.

Research paper thumbnail of Power factor enhancement in a composite based on the half-Heusler antimonide TmNiSb

Journal of Applied Physics, 2018

Electrical transport studies of half-Heusler (HH)-based composites (TmNiSb) 1Àx (TmNiSn) x were c... more Electrical transport studies of half-Heusler (HH)-based composites (TmNiSb) 1Àx (TmNiSn) x were carried out in a wide temperature range aimed at searching for possible enhancement in the thermoelectric power factor (PF) over that observed in the parent compound TmNiSb. The best thermoelectric performance was found in the sample with x ¼ 0.25, which showed PF ¼ 1.3 Â 10 À3 W/mK at 1000 K, i.e., about 70% larger than PF of TmNiSb at the same temperature. The PF improvement was obtained due to the formation in the composite system of a microstructure in which semiconducting-like particles of TmNiSb were covered with a metallic layer of TmNiSn. The largest Seebeck coefficient S ¼ 137 lV/K was observed for HH alloy TmNiSb at 560 K. In turn, TmNiSn showed a metallic behavior with small negative thermoelectric power (S ¼-2.6 lV/K).

Research paper thumbnail of Thermoelectric properties of (DyNiSn) 1−x (DyNiSb) x composite

Physica B: Condensed Matter, 2018

High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNi... more High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNiSb) x composite materials have been studied. For bulk pure DyNiSn and DyNiSb samples the Seebeck coefficient reaches-5.5 V/K at 480 K and 120 V/K at 540 K, respectively. Composite materials show metallic-like electrical resistivity and positive sign of Seebeck coefficient with values up to 50 times higher than in pure DyNiSn compound at 1000 K. Only for the sample with x = 0.47, the ball-milling drives to increase of Seebeck coefficient of about 37% at 650 K.

Research paper thumbnail of Magnetocaloric Effect in Antiferromagnetic Half-Heusler Alloy DyNiSb

Acta Physica Polonica A, 2018

The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound ... more The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound DyNiSb were studied on polycrystalline samples. The temperature variations of the magnetization and the heat capacity revealed a phase transition from paramagnetic to antiferromagnetic state at the Néel temperature TN 3.1 K. The compound exhibits normal and inverse magnetocaloric effect with the isothermal magnetic entropy change reaching 5.2 J/(kg K) at 4.8 K for a magnetic field change of 3 T. The estimated refrigerant capacity is about 58 J/kg.

Research paper thumbnail of Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations

Journal of Alloys and Compounds, 2018

Structural, electronic, and transport properties of ScNiSb, ScPdSb, and ScPtSb were investigated ... more Structural, electronic, and transport properties of ScNiSb, ScPdSb, and ScPtSb were investigated from first principles. Electronic band structures derived within the fully relativistic MBJLDA approach were compared with those obtained from the standard GGA calculations. All the compounds studied exhibit indirect narrow band gaps (0.24-0.63 eV). The effective masses of hole-like carriers are relatively small (0.27-0.36), and decrease with an increasing atomic number of the transition metal component. The carrier relaxation time, required for realistic calculations of the electrical conductivity, was approximated within the deformation potential theory. The GGA approach yielded overestimated transport characteristics with respect to those derived within the MBJLDA analysis. The largest power factor of 4-6 mWK −2 m −1) at high temperatures was obtained for ScPtSb. This value is comparable with those observed experimentally for Fe-Nb-Sb half-Heusler alloys, and hence makes ScPtSb a very good candidate material for thermoelectric applications.

Research paper thumbnail of Low-temperature electronic properties and band structures of La TE 2 Si 2 ( TE =Fe, Co, Ag and Au)

Solid State Communications, 2017

Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity... more Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity in YFe 2 Ge 2 we performed physical properties studies and fully relativistic band structure calculations for a few La-based silicides, namely LaFe 2 Si 2 , LaCo 2 Si 2 , LaAg 2 Si 2 and LaAu 2 Si 2. Electrical resistivity and heat capacity measurements revealed decreasing influence of d-electrons of the transition elements on the conduction electron scattering and the Sommerfeld coefficient with increasing the atomic number. Band structure calculations fully corroborated the experimental findings. No superconductivity was found in the investigated compounds down to 0.35 K.

Research paper thumbnail of Low-temperature electronic properties and band structures of La TE 2 Si 2 ( TE =Fe, Co, Ag and Au)

Solid State Communications, 2017

Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity... more Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity in YFe 2 Ge 2 we performed physical properties studies and fully relativistic band structure calculations for a few La-based silicides, namely LaFe 2 Si 2 , LaCo 2 Si 2 , LaAg 2 Si 2 and LaAu 2 Si 2. Electrical resistivity and heat capacity measurements revealed decreasing influence of d-electrons of the transition elements on the conduction electron scattering and the Sommerfeld coefficient with increasing the atomic number. Band structure calculations fully corroborated the experimental findings. No superconductivity was found in the investigated compounds down to 0.35 K.

Research paper thumbnail of Enhanced thermoelectric power factor of half-Heusler solid solution Sc1-xTmxNiSb prepared by high-pressure high-temperature sintering method

Materials Chemistry and Physics, 2019

In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc 1-x Tm x Ni... more In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc 1-x Tm x NiSb (x = 0.0, 0.25, 0.5, 0.75, 1.0) was synthesized by arc melting and subsequent high-pressure high-temperature sintering. The products were examined by means of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The crystal structure of each sample was established to be of the MgAgAs-type, and the cubic lattice parameter was found to behave in accordance to the Vegard's law. The electrical transport properties of the Sc 1-x Tm x NiSb alloys were determined via resistivity and thermoelectric power measurements performed at temperatures 2-950 K. For each sample a semiconducting-like behavior was found with rather small values of the room-temperature resistivity ( = 10-50 m), and fairly large

Research paper thumbnail of Mobility Ratio as a Probe for Guiding Discovery of Thermoelectric Materials: The Case of Half-Heusler Phase ScNiSb1−xTex

Physical Review Applied

Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelec... more Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelectric materials discovery. Using its product-mobility ratio between electrons and holes-it is possible to choose the most promising compound from the series and pave the correct direction of doping. Current work presents positive verification of this approach for ScNiSb, which is anticipated to show superior mobility when tuned towards n-type behavior. In agreement with expectation, the mobility increases by an order of magnitude due to rising tellurium content in the ScNiSb 1−x Te x series. The effect is most likely driven by change of the dominant charge carriers' scattering mechanism from ionized impurity influence to point defect and acoustic phonon interaction. Simultaneously, due to a highly anisotropic conduction band, the effective mass of the carriers rises towards the n-type regime. These two effects lead to an improved thermoelectric power factor of electron-doped samples, up to 40 μWK −2 cm −1 at 740 K for ScNiSb 0.85 Te 0.15. Based on this result, we suggest n-type doping for other rare-earth-based half-Heusler compounds. Representatives of this group exhibit the smallest lattice thermal conductivity in the pristine form among any half-Heusler thermoelectrics, and are anticipated to show comparably good electrical properties to ScNiSb due to their high mobility ratio in favor of electrons.

Research paper thumbnail of Electronic properties of LaTE2Ge2 ( TE  = Fe, Co, Ni, Cu and Ru)

Solid State Communications, 2018

Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray di... more Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray diffraction, magnetization and electrical resistivity measurements performed down to 2 K, supplemented by fully relativistic band structure and Fermi surface calculations. Results of the theoretical investigations of all the compounds are in line with the experimental findings, namely they show decreasing influence of 3d-electrons of the Fe, Co, Ni and Cu atoms on the electronic properties with increasing the atomic mass. In the case of LaFe2Ge2 the electrical resistivity measurements strongly suggest presence of spin fluctuations, which make that system very similar to the unconventional superconductor YFe2Ge2.

Research paper thumbnail of Thermoelectric Performance of the Half-Heusler Phases RNiSb ( R=Sc,Dy,Er,Tm,Lu ): High Mobility Ratio between Majority and Minority Charge Carriers

Physical Review Applied

Deeper understanding of electrical and thermal transport is critical for further development of t... more Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of ScNiSb, DyNiSb, ErNiSb, TmNiSb, and LuNiSb are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except TmNiSb are found to be narrow-gap intrinsic p-type semiconductors with rather light charge carriers. In TmNiSb, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series (17 μW K −2 cm −1 at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from 0.8 × 10 −14 to 2.8 × 10 −14 s. In all the materials studied, the thermal conductivity is between 3 and 6 W m −1 K −1 near room temperature (i.e., smaller than in other pristine d-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of n-type and p-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.

Research paper thumbnail of Thermoelectric properties of (DyNiSn) 1−x (DyNiSb) x composite

Physica B: Condensed Matter, 2018

High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNi... more High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNiSb) x composite materials have been studied. For bulk pure DyNiSn and DyNiSb samples the Seebeck coefficient reaches-5.5 V/K at 480 K and 120 V/K at 540 K, respectively. Composite materials show metallic-like electrical resistivity and positive sign of Seebeck coefficient with values up to 50 times higher than in pure DyNiSn compound at 1000 K. Only for the sample with x = 0.47, the ball-milling drives to increase of Seebeck coefficient of about 37% at 650 K.

Research paper thumbnail of Magnetocaloric Effect in Antiferromagnetic Half-Heusler Alloy DyNiSb

Acta Physica Polonica A, 2018

The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound ... more The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound DyNiSb were studied on polycrystalline samples. The temperature variations of the magnetization and the heat capacity revealed a phase transition from paramagnetic to antiferromagnetic state at the Néel temperature TN 3.1 K. The compound exhibits normal and inverse magnetocaloric effect with the isothermal magnetic entropy change reaching 5.2 J/(kg K) at 4.8 K for a magnetic field change of 3 T. The estimated refrigerant capacity is about 58 J/kg.

Research paper thumbnail of Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations

Journal of Alloys and Compounds, 2018

Research paper thumbnail of Anomalous electronic properties in layered, disordered ZnVSb

Physical Review Materials, 2021

New materials discovery is the driving force for progress in solid state physics and chemistry. H... more New materials discovery is the driving force for progress in solid state physics and chemistry. Here we solve the crystal structure and comprehensively study physical properties of ZnVSb in the polycrystalline form. Synchrotron x-ray diffraction reveals that the compound attains a layered ZrSiS-type structure ($P4$/nmm, aaa = 4.09021(2) \AA{}, ccc = 6.42027(4) \AA{}). The unit cell is composed of a 2D vanadium network separated by Zn-Sb blocks that are slightly distorted from the ideal cubic arrangement. A considerable amount of vacancies were observed on the vanadium and antimony positions; the experimental composition is mathrmZnV0.91mathrmSb0.96{\mathrm{ZnV}}_{0.91}{\mathrm{Sb}}_{0.96}mathrmZnV0.91mathrmSb0.96. Low-temperature x-ray diffraction shows very subtle discontinuity in the lattice parameters around 175 K. Bonding V-V distance is below the critical separation of 2.97 \AA{} known from the literature, which allows for V-V orbital overlap and subsequent metallic conductivity. From ab initio calculations, we found that Zn...

Research paper thumbnail of Origin of the negative temperature coefficient of resistivity in the half-Heusler antimonides LuNiSb and YPdSb

Physical Review B, 2021

The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperatur... more The electrical transport in the half-Heusler phases LuNiSb and YPdSb was measured in a temperature range 2-300 K. For both compounds, the electrical resistivity was found to decrease with increasing temperature, showing a linear-in-T behavior over an extended temperature interval. In order to interpret the experimental data, a two-channel conductivity model was applied, which revealed that not only the semiconducting-like transport but also the metallic-like one exhibit negative temperature coefficients. The unusual behavior in the metallic channel was described within the Cote-Meisel formalism based on the diffraction model of strongly disordered metals. In addition, a weak localization scenario was considered including spin-orbit scattering and Coulomb interaction between conducting electrons. The electron-electron interaction was found most important at the lowest temperatures, where the semiconducting channel becomes ineffective, reminiscent of charge transport confined to a narrow yet finite-size metallic band located inside the semiconducting energy gap. The low-temperature resistivity of YPdSb appeared fully describable in terms of the Altshuler-Aronov quantum correction due to interacting electrons. In turn, the electronic transport in LuNiSb was found affected by the Kondo effect associated with a small amount of paramagnetic impurities present in the specimen investigated. The approach developed for LuNiSb and YPdSb can be applied to other half-Heusler compounds that exhibit atom disorder in their crystal structures.

Research paper thumbnail of Structural, thermodynamic and magnetotransport properties of half-Heusler compound HoPtSb

Journal of Alloys and Compounds, 2020

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Electronic properties of La TE 2 Ge 2 ( TE  = Fe, Co, Ni, Cu and Ru)

Solid State Communications, 2018

Abstract Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of... more Abstract Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray diffraction, magnetization and electrical resistivity measurements performed down to 2 K, supplemented by fully relativistic band structure and Fermi surface calculations. Results of the theoretical investigations of all the compounds are in line with the experimental findings, namely they show decreasing influence of 3d-electrons of the Fe, Co, Ni and Cu atoms on the electronic properties with increasing the atomic mass. In the case of LaFe2Ge2 the electrical resistivity measurements strongly suggest presence of spin fluctuations, which make that system very similar to the unconventional superconductor YFe2Ge2.

Research paper thumbnail of High-temperature power factor of half-Heusler phases RENiSb (RE = Sc, Dy, Ho, Er, Tm, Lu)

Journal of Alloys and Compounds, 2019

This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Research paper thumbnail of Effect of secondary LuNiSn phase on thermoelectric properties of half-Heusler alloy LuNiSb

Materials Today: Proceedings, 2019

We report on the high-temperature (350 K <T< 1000 K) thermoelectric properties of the ternary com... more We report on the high-temperature (350 K <T< 1000 K) thermoelectric properties of the ternary compounds LuNiSb (cubic) and LuNiSn (orthorhombic) and a composite material (LuNiSb)0.5(LuNiSn)0.5. The electrical conductivity in LuNiSn is metallic, while it is semiconducting-like in LuNiSb. The Seebeck coefficient reaches-5.5 µV/K at 700 K for the former compound and 66 µV/K at 607 K for the latter one. The composite sample (LuNiSb)0.5(LuNiSn)0.5 constructed from orthorhombic matrix with cubic inclusions combines the electrical conductivity of LuNiSn with the thermoelectric properties of LuNiSb. Nonetheless, no enhancement of the thermoelectric performance occurs for this material.

Research paper thumbnail of High-temperature thermoelectric properties of half-Heusler phases Er1-xHoxNiSb

Materials Today: Proceedings, 2019

Polycrystalline samples of Er1-xHoxNiSb (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by... more Polycrystalline samples of Er1-xHoxNiSb (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and optical metallography. The results proved the formation of half-Heusler alloys in the entire composition range. Their electrical transport properties (resistivity, thermoelectric power) were studied in the temperature interval 350-1000 K. The measured electrical resistivity spanned between 5 and 25 m. The maximum thermopower of 50-65 V/K was observed at temperatures 500-650 K. Replacing Ho for Er resulted in a non-monotonous variation of the thermoelectric power factor (PF = S 2 /). The largest PF of 4.6 WcmK-2 was found at 660 K for Er0.5Ho0.5NiSb. This value is distinctly larger than PF determined for the terminal phases ErNiSb and HoNiSb.

Research paper thumbnail of Power factor enhancement in a composite based on the half-Heusler antimonide TmNiSb

Journal of Applied Physics, 2018

Electrical transport studies of half-Heusler (HH)-based composites (TmNiSb) 1Àx (TmNiSn) x were c... more Electrical transport studies of half-Heusler (HH)-based composites (TmNiSb) 1Àx (TmNiSn) x were carried out in a wide temperature range aimed at searching for possible enhancement in the thermoelectric power factor (PF) over that observed in the parent compound TmNiSb. The best thermoelectric performance was found in the sample with x ¼ 0.25, which showed PF ¼ 1.3 Â 10 À3 W/mK at 1000 K, i.e., about 70% larger than PF of TmNiSb at the same temperature. The PF improvement was obtained due to the formation in the composite system of a microstructure in which semiconducting-like particles of TmNiSb were covered with a metallic layer of TmNiSn. The largest Seebeck coefficient S ¼ 137 lV/K was observed for HH alloy TmNiSb at 560 K. In turn, TmNiSn showed a metallic behavior with small negative thermoelectric power (S ¼-2.6 lV/K).

Research paper thumbnail of Thermoelectric properties of (DyNiSn) 1−x (DyNiSb) x composite

Physica B: Condensed Matter, 2018

High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNi... more High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn) 1x (DyNiSb) x composite materials have been studied. For bulk pure DyNiSn and DyNiSb samples the Seebeck coefficient reaches-5.5 V/K at 480 K and 120 V/K at 540 K, respectively. Composite materials show metallic-like electrical resistivity and positive sign of Seebeck coefficient with values up to 50 times higher than in pure DyNiSn compound at 1000 K. Only for the sample with x = 0.47, the ball-milling drives to increase of Seebeck coefficient of about 37% at 650 K.

Research paper thumbnail of Magnetocaloric Effect in Antiferromagnetic Half-Heusler Alloy DyNiSb

Acta Physica Polonica A, 2018

The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound ... more The low-temperature magnetic, thermal and magnetocaloric properties of the half-Heusler compound DyNiSb were studied on polycrystalline samples. The temperature variations of the magnetization and the heat capacity revealed a phase transition from paramagnetic to antiferromagnetic state at the Néel temperature TN 3.1 K. The compound exhibits normal and inverse magnetocaloric effect with the isothermal magnetic entropy change reaching 5.2 J/(kg K) at 4.8 K for a magnetic field change of 3 T. The estimated refrigerant capacity is about 58 J/kg.

Research paper thumbnail of Thermoelectric performance of p-type half-Heusler alloys ScMSb (M = Ni, Pd, Pt) by ab initio calculations

Journal of Alloys and Compounds, 2018

Structural, electronic, and transport properties of ScNiSb, ScPdSb, and ScPtSb were investigated ... more Structural, electronic, and transport properties of ScNiSb, ScPdSb, and ScPtSb were investigated from first principles. Electronic band structures derived within the fully relativistic MBJLDA approach were compared with those obtained from the standard GGA calculations. All the compounds studied exhibit indirect narrow band gaps (0.24-0.63 eV). The effective masses of hole-like carriers are relatively small (0.27-0.36), and decrease with an increasing atomic number of the transition metal component. The carrier relaxation time, required for realistic calculations of the electrical conductivity, was approximated within the deformation potential theory. The GGA approach yielded overestimated transport characteristics with respect to those derived within the MBJLDA analysis. The largest power factor of 4-6 mWK −2 m −1) at high temperatures was obtained for ScPtSb. This value is comparable with those observed experimentally for Fe-Nb-Sb half-Heusler alloys, and hence makes ScPtSb a very good candidate material for thermoelectric applications.

Research paper thumbnail of Low-temperature electronic properties and band structures of La TE 2 Si 2 ( TE =Fe, Co, Ag and Au)

Solid State Communications, 2017

Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity... more Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity in YFe 2 Ge 2 we performed physical properties studies and fully relativistic band structure calculations for a few La-based silicides, namely LaFe 2 Si 2 , LaCo 2 Si 2 , LaAg 2 Si 2 and LaAu 2 Si 2. Electrical resistivity and heat capacity measurements revealed decreasing influence of d-electrons of the transition elements on the conduction electron scattering and the Sommerfeld coefficient with increasing the atomic number. Band structure calculations fully corroborated the experimental findings. No superconductivity was found in the investigated compounds down to 0.35 K.

Research paper thumbnail of Low-temperature electronic properties and band structures of La TE 2 Si 2 ( TE =Fe, Co, Ag and Au)

Solid State Communications, 2017

Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity... more Motivated by recent discovery of a non-Fermi liquid behavior and unconventional superconductivity in YFe 2 Ge 2 we performed physical properties studies and fully relativistic band structure calculations for a few La-based silicides, namely LaFe 2 Si 2 , LaCo 2 Si 2 , LaAg 2 Si 2 and LaAu 2 Si 2. Electrical resistivity and heat capacity measurements revealed decreasing influence of d-electrons of the transition elements on the conduction electron scattering and the Sommerfeld coefficient with increasing the atomic number. Band structure calculations fully corroborated the experimental findings. No superconductivity was found in the investigated compounds down to 0.35 K.

Research paper thumbnail of Enhanced thermoelectric power factor of half-Heusler solid solution Sc1-xTmxNiSb prepared by high-pressure high-temperature sintering method

Materials Chemistry and Physics, 2019

In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc 1-x Tm x Ni... more In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc 1-x Tm x NiSb (x = 0.0, 0.25, 0.5, 0.75, 1.0) was synthesized by arc melting and subsequent high-pressure high-temperature sintering. The products were examined by means of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The crystal structure of each sample was established to be of the MgAgAs-type, and the cubic lattice parameter was found to behave in accordance to the Vegard's law. The electrical transport properties of the Sc 1-x Tm x NiSb alloys were determined via resistivity and thermoelectric power measurements performed at temperatures 2-950 K. For each sample a semiconducting-like behavior was found with rather small values of the room-temperature resistivity ( = 10-50 m), and fairly large

Research paper thumbnail of Mobility Ratio as a Probe for Guiding Discovery of Thermoelectric Materials: The Case of Half-Heusler Phase ScNiSb1−xTex

Physical Review Applied

Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelec... more Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelectric materials discovery. Using its product-mobility ratio between electrons and holes-it is possible to choose the most promising compound from the series and pave the correct direction of doping. Current work presents positive verification of this approach for ScNiSb, which is anticipated to show superior mobility when tuned towards n-type behavior. In agreement with expectation, the mobility increases by an order of magnitude due to rising tellurium content in the ScNiSb 1−x Te x series. The effect is most likely driven by change of the dominant charge carriers' scattering mechanism from ionized impurity influence to point defect and acoustic phonon interaction. Simultaneously, due to a highly anisotropic conduction band, the effective mass of the carriers rises towards the n-type regime. These two effects lead to an improved thermoelectric power factor of electron-doped samples, up to 40 μWK −2 cm −1 at 740 K for ScNiSb 0.85 Te 0.15. Based on this result, we suggest n-type doping for other rare-earth-based half-Heusler compounds. Representatives of this group exhibit the smallest lattice thermal conductivity in the pristine form among any half-Heusler thermoelectrics, and are anticipated to show comparably good electrical properties to ScNiSb due to their high mobility ratio in favor of electrons.

Research paper thumbnail of Electronic properties of LaTE2Ge2 ( TE  = Fe, Co, Ni, Cu and Ru)

Solid State Communications, 2018

Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray di... more Nonmagnetic germanides LaTE2Ge2 with TE = Fe, Co, Ni, Cu and Ru were studied by means of X-ray diffraction, magnetization and electrical resistivity measurements performed down to 2 K, supplemented by fully relativistic band structure and Fermi surface calculations. Results of the theoretical investigations of all the compounds are in line with the experimental findings, namely they show decreasing influence of 3d-electrons of the Fe, Co, Ni and Cu atoms on the electronic properties with increasing the atomic mass. In the case of LaFe2Ge2 the electrical resistivity measurements strongly suggest presence of spin fluctuations, which make that system very similar to the unconventional superconductor YFe2Ge2.

Research paper thumbnail of Thermoelectric Performance of the Half-Heusler Phases RNiSb ( R=Sc,Dy,Er,Tm,Lu ): High Mobility Ratio between Majority and Minority Charge Carriers

Physical Review Applied

Deeper understanding of electrical and thermal transport is critical for further development of t... more Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of ScNiSb, DyNiSb, ErNiSb, TmNiSb, and LuNiSb are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except TmNiSb are found to be narrow-gap intrinsic p-type semiconductors with rather light charge carriers. In TmNiSb, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series (17 μW K −2 cm −1 at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from 0.8 × 10 −14 to 2.8 × 10 −14 s. In all the materials studied, the thermal conductivity is between 3 and 6 W m −1 K −1 near room temperature (i.e., smaller than in other pristine d-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of n-type and p-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.