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Novel filled skutterudites BayNi4Sb12−xSnx(ymax= 0.93) have been prepared and thoroughly characterized, which show anomalously high lattice thermal conductivity.
Research Interests: Condensed Matter Physics, Materials Science, Chemistry, Inorganic Chemistry, Medicine, and 12 moreMechanical properties, Phase equilibria, Severe Plastic Deformation, Physical sciences, Electronic Structure, Thermal Conductivity, Science Technology, Electrical Resistivity, Physical Properties, High Pressure Torsion, thermoelectric properties, and stage IV
We investigate the crystal structures and physical properties of novel Ba5{V,Nb}12Sb19+x compounds.
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Abstract : Information on phase equilibria and compound formation in the Li-B-N system all agree on the existence of a ternary compound Li3Bn2 with several pressure modifications. Heating powder compacts of Li3N + BN in a Mo-boat in a... more
Abstract : Information on phase equilibria and compound formation in the Li-B-N system all agree on the existence of a ternary compound Li3Bn2 with several pressure modifications. Heating powder compacts of Li3N + BN in a Mo-boat in a stream of nitrogen between 650 to 700 C was claimed as optimal conditions to obtain Li3BN2 the reaction being strongly exothermic. Melting of Li3BN2 was reported at 870. Based on earlier preliminary data by the p-T diagram of Li3BN2 was investigated over the pressure and temperature range from 1.0 to 6.5 GPa and 300 to 1900 C employing optical and x-ray powder diffraction analysis.
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The peculiarities of the temperature and concentration characteristics of resistivity and thermopower of V1-xTixFeSb semiconductor solid solution were investigated in the temperature and concentration ranges of T = 4.2 -400 K and Ті ≈... more
The peculiarities of the temperature and concentration characteristics of resistivity and thermopower of V1-xTixFeSb semiconductor solid solution were investigated in the temperature and concentration ranges of T = 4.2 -400 K and Ті ≈ 9.5·1019–3.6·1021 см-3 (х = 0.005 - 0.20), respectively. The existence of previously unknown mechanism for the generation of structural defects with donor nature which determined the conduction of n-VFeSb and V1-xTixFeSb was established. The acceptor type of structural defects generated in V1-xTixFeSb by substitution of V atoms by Ti ones was confirmed.
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ABSTRACTQuantitative X-ray powder Rietveld refinements for a series of alloys from the solid solution EuyFe4−xNixSb12, synthesized by argon arc-melting followed by long term annealing, established in all cases isotypism with the partially... more
ABSTRACTQuantitative X-ray powder Rietveld refinements for a series of alloys from the solid solution EuyFe4−xNixSb12, synthesized by argon arc-melting followed by long term annealing, established in all cases isotypism with the partially filled skutterudite-type structure, LaFe4P12. The Eucontent of the samples was determined from the combined data obtained results of Rietveld refinements and electron microprobe measurements. These investigations confirmed a systematic trend for the Eu-occupancy y in the parent lattice, revealing a gradual decrease of the maximum Eu-content from practically full occupancy, y = 0.83, in Eu0.83Fe4Sb12 to y ∼ 0.5 for Eu∼0.5Fe2Ni2Sb12. Eu0.83Fe4Sb12 orders magnetically below 84 K and the transition temperature decreases as a function of Fe/Ni substitution. As a further consequence of the Fe/Ni substitution electronic transport crosses over from a hole conductivity regime into electron dominated behaviour. Concomitantly, the transition metal exchange in...
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The best p-type skutterudites with ZT > 1.1 so far are didymium (DD) filled, Fe/Co substituted, Sb-based skutterudites. DD0.68Fe3CoSb12 was prepared using an annealing-reacting-melting-quenching technique followed by ball milling and... more
The best p-type skutterudites with ZT > 1.1 so far are didymium (DD) filled, Fe/Co substituted, Sb-based skutterudites. DD0.68Fe3CoSb12 was prepared using an annealing-reacting-melting-quenching technique followed by ball milling and hot pressing. After severe plastic deformation via high-pressure torsion (HPT), no phase changes but particular structural variations were achieved, leading to modified transport properties with higher ZT values. Although after measurement-induced heating some of the HPT induced defects were annealed out, a still attractive ZT-value was preserved. In this paper we focus on explanations for these changes via TEM investigations, Raman spectroscopy and texture measurements. The grain sizes and dislocation densities, evaluated from TEM images, showed that (i) the majority of cracks generated during high-pressure torsion are healed during annealing, leaving only small pores, that (ii) the grains have grown, and that (iii) the dislocation density is decrea...
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The crystal structures of two novel borides τ5-Ni3Zn2B and τ6-Ni2ZnB, were determined. For these newly found phases as well as for τ3-Ni21Zn2B20 and τ4-Ni3ZnB2 density functional theory calculations (DFT-VASP) were performed.
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The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (BiTe) nanoinclusions in CoSb leads to lower phonon thermal conductivity by... more
The figure of merit (zT) of a thermoelectric material can be enhanced by incorporation of nanoinclusions into bulk material. The presence of bismuth telluride (BiTe) nanoinclusions in CoSb leads to lower phonon thermal conductivity by introducing interfaces and defects; it enhances the average zT between 300-700 K. In the current study, BiTe nanoparticles were dispersed into bulk CoSb by ball-milling. The bulk was fabricated by spark plasma sintering. The presence of BiTe dispersion in CoSb was confirmed by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and electron back scattered diffraction technique. Energy dispersive spectroscopy showed antimony (Sb) as an impurity phase for higher contents of BiTe in the sample. The Seebeck coefficient (S) and electrical conductivity (σ) were measured in the temperature range of 350-673 K. The negative value of S indicates that most of the charge carriers were electrons. A decrease in S and increase in σ with ...
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Thermoelectric materials are actively considered for waste heat recovery applications. To improve the heat to electricity conversion efficiency, fundamental understanding on composition, crystal structure, and interrelation with the... more
Thermoelectric materials are actively considered for waste heat recovery applications. To improve the heat to electricity conversion efficiency, fundamental understanding on composition, crystal structure, and interrelation with the thermoelectric properties is necessary. Here, we report the chemical and thermoelectric properties of type-I clathrates Ba 8 Ni 3.8 Si x Ge 42.2 - x ( = 0, 10, 20, 42.2), to show that the Si substitution can retain the low lattice thermal conductivity as in pure Ge-based clathrates by adding defects (cage distortion) scattering and/or alloying effect, and the charge carrier concentration can be optimized and thus the electronic properties can be improved by tailoring the vacancy content. We demonstrate the vacancies in the pure Ge-based compound by Rietveld refinement, and possible vacancies in the quaternary compound by transport property measurements. We also show that, for intrinsic property studies in these compounds with such a complex crystal struc...
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A new compound YbFe4Sb12 was synthesized by reaction sintering. It belongs to the family of ternary filled skutterudites. The crystal structure was determined from single crystal X-ray counter data: LaFe4P12-(skutterudite)-type, space... more
A new compound YbFe4Sb12 was synthesized by reaction sintering. It belongs to the family of ternary filled skutterudites. The crystal structure was determined from single crystal X-ray counter data: LaFe4P12-(skutterudite)-type, space group Im3−Th5 No. 204, Z=2, a=0.91571(5)nm; residual values: RF=3.0, wR=6.9, GOF=1.316. Magnetic susceptibility and magnetization data assisted by 57Fe Mössbauer and XAS spectra revealed that the compound is a
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... i0000i-< i0 -< I>tDCOlOOS tO CM 0 10 q'i-llOlO^ 001CO c-ii-icoco oo OiOiOlO O o oo 0l iTi crt-tOtO t>c ... occupation of the corresponding coordination figures, and thus from structural arguments it is concluded that... more
... i0000i-< i0 -< I>tDCOlOOS tO CM 0 10 q'i-llOlO^ 001CO c-ii-icoco oo OiOiOlO O o oo 0l iTi crt-tOtO t>c ... occupation of the corresponding coordination figures, and thus from structural arguments it is concluded that the structure modi-fication with the shorter Ce-Ce distances (ThCr ...
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ABSTRACT It is well known that the process variables for sample synthesis affect the electrical, magnetic, mechanical, etc. properties of the final product. In this study, we present the influence of the hot pressing temperature on the... more
ABSTRACT It is well known that the process variables for sample synthesis affect the electrical, magnetic, mechanical, etc. properties of the final product. In this study, we present the influence of the hot pressing temperature on the thermoelectric properties of a type-I clathrate of nominal composition Ba8Cu4.5Ge35.5Si6. The samples are prepared in a high-frequency furnace, annealed, and subject to a long-time ball milling. Finally, the nanopowders from ball milling are hot pressed at different temperatures. All hot pressed samples are characterized by X-ray diffraction, energy dispersive X-ray spectroscope, scanning electron microscopy, and transport property measurements. The results show that lower hot pressing temperatures are desired to prevent the nanopowders from coarsening, but are unfavorable for the densification: Samples hot pressed at lower temperatures have smaller crystallite sizes, larger porosities, and lower relative densities and, consequently, have higher electrical resistivity, and lower thermal conductivity. No significant differences are seen in ZT as the positive effect of reduced thermal conductivity is compensated by the enhanced electrical resistivity. The highest ZT of 0.42 is reached at 873 K for a sample hot pressed at 780 °C.
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ABSTRACTOn the search for cost-competitive thermoelectric clathrates we have investigated the influence of Sn substitutions for Ge on the structural and thermoelectric properties of the type-I clathrate Ba8Cu5Si6Ge35. The solid solubility... more
ABSTRACTOn the search for cost-competitive thermoelectric clathrates we have investigated the influence of Sn substitutions for Ge on the structural and thermoelectric properties of the type-I clathrate Ba8Cu5Si6Ge35. The solid solubility of Sn was found to be limited to 0.6 atoms per unit cell. A series of compounds with the nominal compositions Ba8Cu5Si6Ge35-xSnx (x = 0.2, 0.4, 0.6) was synthesized in a high-frequency furnace. The samples were annealed, and subsequently ball milled and hot pressed. The hot pressed samples were characterized by X-ray powder diffraction, energy-dispersive X-ray spectroscopy and transport property measurements. Our results show that the substitution of Ge by Sn introduces vacancies at the 6d site of the type-I clathrate structure and shifts the highest dimensionless thermoelectric figure of merit ZT from 570 °C for the Sn free sample to lower temperatures. The highest figure of merit ZT = 0.42 is reached at about 320 °C for the Sn-substituted sample Ba8Cu5Si6Ge35Sn0.6.
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A new member of the series of Th7 Fe3 -type derivative structures, h-(Pd0.86 Cu0.14 )7 B3 (≡Pd6.02 Cu0.98 B3 , unique structure type Pd6 CuB3 , space group P63 cm, a=12.9426(9) Å, c=4.8697(4) Å, single-crystal X-ray diffraction (XRD)... more
A new member of the series of Th7 Fe3 -type derivative structures, h-(Pd0.86 Cu0.14 )7 B3 (≡Pd6.02 Cu0.98 B3 , unique structure type Pd6 CuB3 , space group P63 cm, a=12.9426(9) Å, c=4.8697(4) Å, single-crystal X-ray diffraction (XRD) data) was obtained from as cast alloys and alloys annealed at 600-650 °C. Further substitution of Cu by Pd led to formation of a Mn7 C3 -type structure, o-(Pd0.93 Cu0.07 )7 B3 (≡Pd6.51 Cu0.49 B3 , space group Pnma, a=4.8971(2) Å, b=7.5353(3) Å, c=12.9743(6) Å, single-crystal XRD). Isotypic LT h-(Pt0.70 Cu0.30 )7 B3 (≡Pt4.90 Cu2.10 B3 ) was observed in the Pt-Cu-B system as a low-temperature (LT) phase (T≤600 °C) (powder XRD), whereas the Th7 Fe3 -type (high-temperature (HT) h-(Pt0.73 Cu0.27 )7 B3 ≡Pt5.11 Cu1.89 B3 , space group P63 mc, a=7.4671(1) Å, c=4.9039(1) Å, powder XRD) proved to be stable at high temperature. The three structures are built of columns of face connected metal octahedra and columns of metal tetrahedra alternatingly fused by common ...
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Transport and magnetic properties are reported for ternary skutterudites La 0.83 Fe 4 Sb 12 and Pr 0.73 Fe 4 Sb 12. Physical properties of Pr 0.73 Fe 4 Sb 12 are dominated by crystal electric field effects, yielding in the magnetic... more
Transport and magnetic properties are reported for ternary skutterudites La 0.83 Fe 4 Sb 12 and Pr 0.73 Fe 4 Sb 12. Physical properties of Pr 0.73 Fe 4 Sb 12 are dominated by crystal electric field effects, yielding in the magnetic triplet Γ 5 as ground state. As a result, long-...
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