Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 ... more Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 .-The title compound is synthesized from stoichiometric mixtures of the elements (800°C, 3 d). As revealed by single crystal XRD it crystallizes in the space group P21/m with Z = 4. The structure contains corner-, edge-, and face-sharing CuTe4 tetrahedra interconnected with almost planar CuTe3 units and dumbbells resulting in a three-dimensional copper network. The material is a degenerate semiconductor with moderate Seebeck coefficient and electrical conductivity, in accord with LMTO calculations, and exhibits extremely low thermal conductivity.
Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved ... more Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved effective in enhancing their thermoelectric performance. In this paper we report the effects of (In,Yb) double filling on the high temperature thermoelectric properties of CoSb3. The InxYbyCo4Sb12 (0≤(x,y)≤0.2) samples have been prepared via a melting-annealing-sintering procedure and characterized by means of x-ray powder diffraction, scanning electron microscopy, Hall coefficient, electrical and thermal conductivities, and Seebeck coefficient measurements. As compared to the In and Yb single-filling approach, the (In,Yb) double-filling approach can effectively reduce the lattice thermal conductivity without degrading the power factor. As a result, several compositions achieve ZT values around unity, while a maximum ZT value of 1.1 is obtained in In0.2Yb0.1Co4Sb12 at 700 K. The difference in the effects of In and Yb filling on the thermoelectric properties is discussed.
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current value... more For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 ... more Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 .-The title compound is synthesized from stoichiometric mixtures of the elements (800°C, 3 d). As revealed by single crystal XRD it crystallizes in the space group P21/m with Z = 4. The structure contains corner-, edge-, and face-sharing CuTe4 tetrahedra interconnected with almost planar CuTe3 units and dumbbells resulting in a three-dimensional copper network. The material is a degenerate semiconductor with moderate Seebeck coefficient and electrical conductivity, in accord with LMTO calculations, and exhibits extremely low thermal conductivity.
We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO 3 ceramics via a ... more We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO 3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using Xray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO 3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO 3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO 3 .
Tin atoms were inserted into the skutterudite-type CoSb3 host lattice under high pressure and tem... more Tin atoms were inserted into the skutterudite-type CoSb3 host lattice under high pressure and temperature
We demonstrate the potential of polymer-derived ceramics (PDC) as next-generation sustainable the... more We demonstrate the potential of polymer-derived ceramics (PDC) as next-generation sustainable thermoelectrics. Thermoelectric behavior of polymer-derived silicon oxycarbide (SiOC) ceramics (containing hexagonal boron nitride (h-BN) as filler) was studied as a function of measurement temperature. SiOC, sintered at 1300 °C exhibited invariant low thermal conductivity (~ 1.5 W/m-K) over 30-600 °C, coupled with a small increase in both Seebeck coefficient and electrical conductivity, with increase in measurement temperature (30-150 °C). SiOC ceramics containing 1 wt. % h-BN showed the highest Seebeck coefficient (-33 µV/K) for any PDC thus far.
Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler... more Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in view of thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900 o C, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to improved structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys.
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current value... more For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
Interface modification in transport properties of single elemental polycrystalline Bi via spark p... more Interface modification in transport properties of single elemental polycrystalline Bi via spark plasma sintering results in 'double-decoupling' (simultaneous decoupling of thermopower, electrical, and thermal conductivity) of otherwise coupled entities. In spark plasma sintering, the DC pulse current helps in controlling the nature and extent of surfaces of ball-milled Bi and hence results in six-fold improvement in the dimensionless figure of merit (ZT) relative to as-purchased samples.
Herein, we report the effects of indium (In) incorporation upon the thermoelectric and magnetic p... more Herein, we report the effects of indium (In) incorporation upon the thermoelectric and magnetic properties of Ni doped Fe-based filled skutterudites (InxCe0.9Fe3.5Ni0.5Sb12 with x = 0, 0.1, and 0.5). We find that secondary phases (such as InSb) can be formed upon surpassing the filling fraction limit and these in turn result in improved thermoelectric properties. A maximum dimensionless figure of merit, ZT ≈ 0.9 at ∼650 K was obtained for the sample with the nominal composition In0.1Ce0.9Fe3.5Ni0.5Sb12. Interestingly, we also observe Kondo-like behavior and evidence of the crystal field effect in these samples. The low-temperature (T < 100 K) thermopower and electrical resistivity of our samples exhibit Kondo-like behavior while their corresponding magnetic susceptibility suggests that the Ce3+ ions are influenced by the cubic crystal symmetry of the skutterudites class of materials, thus resulting in the crystal field effect. Lastly, the magnetic susceptibility data can be interpreted in the context of a second-order perturbation model.
Void-filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proven ... more Void-filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proven to be an effective mechanism to enhance thermoelectric performance due primarily to a reduction in lattice thermal conductivity. Specifically, our findings on the series In x Yb y Co4Sb12 [0 ≤ (x, y) ≤ 0.2] have further motivated an attempt to form triple-filled skutterudites Ce0.1In x Yb y Co4Sb12 with
Eighteenth International Conference on Thermoelectrics. Proceedings, ICT'99 (Cat. No.99TH8407)
Filled skutterudite antimonides are an example of electron crystal and phonon-glass materials as ... more Filled skutterudite antimonides are an example of electron crystal and phonon-glass materials as originally proposed by Slack (1994). A properly optimized compound should exhibit high electrical conductivity and Seebeck coefficients in combination with a very low thermal conductivity, thus resulting in a high value for ZT. In skutterudites, the low thermal conductivity results from the incoherent rattling of the loosely
ABSTRACTCompounds with clathrate-hydrate type crystal lattice structures are currently of interes... more ABSTRACTCompounds with clathrate-hydrate type crystal lattice structures are currently of interest in thermoelectric materials research. This is due to the fact that semiconducting compounds can be synthesized with varying doping levels while possessing low, even ‘glass-like’, thermal conductivity. Up to now most of the work has focused on type I Si and Ge clathrates. Sn-clathrates however are viewed as having the greatest potential for thermoelectric cooling applications due to the larger mass of Sn and the expected small band-gap, as compared to Si and Ge clathrates. Transport properties on type I Sn-clathrates has only recently been reported [1–3]. In this report we present ongoing experimental research on both type I and II clathrates with an emphasis on the thermal transport of these novel materials. We present thermal conductivity data Si-Ge and Ge-Sn alloys as well as on a type II Ge clathrate for the first time, and compare these data to that of other clathrate compounds.
ABSTRACTThe pentatelluride materials (Hf1-XZrXTe5) have recently garnered much interest as a pote... more ABSTRACTThe pentatelluride materials (Hf1-XZrXTe5) have recently garnered much interest as a potential low temperature thermoelectric material. Their power factor exceeds that of the current Bi2Te3 materials over the temperature range 150 K < T < 350 K. A formidable challenge has been the capability of measuring the thermal conductivity of small needle-like samples (2.0 × 0.05 × 0.1 mm3) such as pentatellurides (HfXZr1-XTe5) due to heat loss and radiation effects. However in order to fully evaluate any material for potential thermoelectric use, the determination of the thermal conductivity of the material is necessary. We have recently developed a new technique called the parallel thermal conductance (PTC) technique to measure the thermal conductivity of such small samples. In this paper we describe the PTC method and measurements of the thermal conductivity of the pentatelluride materials will be presented for the first time. The potential of these materials for low temperatu...
ABSTRACTFilled skutterudite compounds possess very low thermal conductivities due to the scatteri... more ABSTRACTFilled skutterudite compounds possess very low thermal conductivities due to the scattering of a wide range of phonon modes caused by a loosely bound cation incorporated in a cavity of the structure. The inclusion of such a filler cation causes several synthetic difficulties since the desired compounds are thermodynamically unstable with respect to disproportionation. Modulated elemental reactants were used in this study to circumvent these difficulties. SnxCo4Sb12 samples with x=0.5 and nearly 1.0 were synthesized using this method. To prevent nucleation of unwanted binary compounds, the repeat unit made up of elemental layers was less than 20 angstroms 500mg of each sample were produced, allowing for the samples to be hot pressed into a pellet. Structural analysis as well as measurements of the physical properties are presented.
ABSTRACTThe skutterudite family of compounds continues to be of interest for thermoelectric appli... more ABSTRACTThe skutterudite family of compounds continues to be of interest for thermoelectric applications due to the low thermal conductivity obtained when filling the voids with small diameter, large mass interstitials such as trivalent rare-earth ions. In the last few years there has been a substantial experimental and theoretical effort in attempting to understand the transport properties of these compounds in order to optimize their thermoelectric properties. One such approach involves partially-filling the voids in attempting to optimize the power factor while maintaining low thermal conductivity. In this report experimental research on skutterudites with the voids partially filled with heavy mass lanthanide and alkaline-earth ions is reported.
Over the past decade, the open frame ("cagey") structure of CoSb 3 skutterudite has invited inten... more Over the past decade, the open frame ("cagey") structure of CoSb 3 skutterudite has invited intensive filling studies with various rare-earth elements for delivering state-of-theart mid-temperature thermoelectric performance. To rationalize previously reported experimental results and provide new insight into the underexplored roles of La fillers and Sb vacancies, ab initio density functional theory studies, along with semi-classical Boltzmann transport theory calculations, are performed for pristine CoSb 3 of different lattice settings and La-filled CoSb 3 with and without Sb's mono-and di-vacancy defects. The effects of spin-orbit coupling (SOC), partial La-filling, Sb vacancy defects, and spin polarization on the electronic and thermoelectric properties are systematically examined. The SOC shows minor effects on the electronic and thermoelectric properties of CoSb 3. The peculiar quasi-Dirac band in the pristine CoSb 3 largely survives La filling but not Sb vacancies, which instead introduce dispersive bands in the band gap region. The non-spin-polarized and spin-polarized solutions of La-filled CoSb 3 are nearly degenerate. Importantly, the band structure, density of states, and Fermi surface of the latter are significantly spin polarized, giving rise to spin-dependent thermoelectric properties. Seebeck coefficients directly calculated as a function of chemical potential are interpreted in connection with the electronic structures. Temperature-dependent Seebeck coefficients derived for the experimentally studied materials agree well with available experimental data. Seebeck coefficients obtained as a function of charge carrier concentration corroborate the thermoelectrically favorable role at high filling fractions played by the Fermi electron pockets associated with the degenerate valleys in the conduction bands, and also point toward a similar role of the Fermi hole pockets associated with the degenerate hills in the valence bands. These results serve to advance the understanding of CoSb 3 skutterudite, a class of materials with important fundamental and application implications for thermoelectrics and spintronics.
Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 ... more Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 .-The title compound is synthesized from stoichiometric mixtures of the elements (800°C, 3 d). As revealed by single crystal XRD it crystallizes in the space group P21/m with Z = 4. The structure contains corner-, edge-, and face-sharing CuTe4 tetrahedra interconnected with almost planar CuTe3 units and dumbbells resulting in a three-dimensional copper network. The material is a degenerate semiconductor with moderate Seebeck coefficient and electrical conductivity, in accord with LMTO calculations, and exhibits extremely low thermal conductivity.
Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved ... more Void filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proved effective in enhancing their thermoelectric performance. In this paper we report the effects of (In,Yb) double filling on the high temperature thermoelectric properties of CoSb3. The InxYbyCo4Sb12 (0≤(x,y)≤0.2) samples have been prepared via a melting-annealing-sintering procedure and characterized by means of x-ray powder diffraction, scanning electron microscopy, Hall coefficient, electrical and thermal conductivities, and Seebeck coefficient measurements. As compared to the In and Yb single-filling approach, the (In,Yb) double-filling approach can effectively reduce the lattice thermal conductivity without degrading the power factor. As a result, several compositions achieve ZT values around unity, while a maximum ZT value of 1.1 is obtained in In0.2Yb0.1Co4Sb12 at 700 K. The difference in the effects of In and Yb filling on the thermoelectric properties is discussed.
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current value... more For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 ... more Electric properties D 8000 Thermoelectric Properties of the New Polytelluride Ba 3 Cu 14-δ Te 12 .-The title compound is synthesized from stoichiometric mixtures of the elements (800°C, 3 d). As revealed by single crystal XRD it crystallizes in the space group P21/m with Z = 4. The structure contains corner-, edge-, and face-sharing CuTe4 tetrahedra interconnected with almost planar CuTe3 units and dumbbells resulting in a three-dimensional copper network. The material is a degenerate semiconductor with moderate Seebeck coefficient and electrical conductivity, in accord with LMTO calculations, and exhibits extremely low thermal conductivity.
We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO 3 ceramics via a ... more We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO 3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using Xray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO 3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO 3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO 3 .
Tin atoms were inserted into the skutterudite-type CoSb3 host lattice under high pressure and tem... more Tin atoms were inserted into the skutterudite-type CoSb3 host lattice under high pressure and temperature
We demonstrate the potential of polymer-derived ceramics (PDC) as next-generation sustainable the... more We demonstrate the potential of polymer-derived ceramics (PDC) as next-generation sustainable thermoelectrics. Thermoelectric behavior of polymer-derived silicon oxycarbide (SiOC) ceramics (containing hexagonal boron nitride (h-BN) as filler) was studied as a function of measurement temperature. SiOC, sintered at 1300 °C exhibited invariant low thermal conductivity (~ 1.5 W/m-K) over 30-600 °C, coupled with a small increase in both Seebeck coefficient and electrical conductivity, with increase in measurement temperature (30-150 °C). SiOC ceramics containing 1 wt. % h-BN showed the highest Seebeck coefficient (-33 µV/K) for any PDC thus far.
Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler... more Half-Heusler alloys (MgAgSb structure) are promising thermoelectric materials. RNiSn half-Heusler phases (R=Hf, Zr, Ti) are the most studied in view of thermal stability. The highest dimensionless figure of merit (ZT) obtained is ~1 in the temperature range ~450-900 o C, primarily achieved in nanostructured alloys. Through proper annealing, ZT~1.2 has been obtained in a previous ZT~1 n-type (Hf,Zr)NiSn phase without the nanostructure. There is an appreciable increase in power factor, decrease in charge carrier density, and increase in carrier mobility. The findings are attributed to improved structural order. Present approach may be applied to optimize the functional properties of Heusler-type alloys.
For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current value... more For bulk thermoelectrics, improvement of the figure of merit ZT to above 2 from the current values of 1.0 to 1.5 would enhance their competitiveness with alternative technologies. In recent years, the most significant improvements in ZT have mainly been due to successful reduction of thermal conductivity. However, thermal conductivity is difficult to measure directly at high temperatures. Combined measurements of thermal diffusivity, specific heat, and mass density are a widely used alternative to direct measurement of thermal conductivity. In this work, thermal conductivity is shown to be the factor in the calculation of ZT with the greatest measurement uncertainty. The International Energy Agency (IEA) group, under the implementing agreement for Advanced Materials for Transportation (AMT), has conducted two international round-robins since 2009. This paper, part II of our report on the international round-robin testing of transport properties of bulk bismuth telluride, focuses on thermal diffusivity, specific heat, and thermal conductivity measurements.
Interface modification in transport properties of single elemental polycrystalline Bi via spark p... more Interface modification in transport properties of single elemental polycrystalline Bi via spark plasma sintering results in &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;double-decoupling&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39; (simultaneous decoupling of thermopower, electrical, and thermal conductivity) of otherwise coupled entities. In spark plasma sintering, the DC pulse current helps in controlling the nature and extent of surfaces of ball-milled Bi and hence results in six-fold improvement in the dimensionless figure of merit (ZT) relative to as-purchased samples.
Herein, we report the effects of indium (In) incorporation upon the thermoelectric and magnetic p... more Herein, we report the effects of indium (In) incorporation upon the thermoelectric and magnetic properties of Ni doped Fe-based filled skutterudites (InxCe0.9Fe3.5Ni0.5Sb12 with x = 0, 0.1, and 0.5). We find that secondary phases (such as InSb) can be formed upon surpassing the filling fraction limit and these in turn result in improved thermoelectric properties. A maximum dimensionless figure of merit, ZT ≈ 0.9 at ∼650 K was obtained for the sample with the nominal composition In0.1Ce0.9Fe3.5Ni0.5Sb12. Interestingly, we also observe Kondo-like behavior and evidence of the crystal field effect in these samples. The low-temperature (T &lt; 100 K) thermopower and electrical resistivity of our samples exhibit Kondo-like behavior while their corresponding magnetic susceptibility suggests that the Ce3+ ions are influenced by the cubic crystal symmetry of the skutterudites class of materials, thus resulting in the crystal field effect. Lastly, the magnetic susceptibility data can be interpreted in the context of a second-order perturbation model.
Void-filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proven ... more Void-filling in the CoSb3 skutterudite lattice with different kinds of heavy elements has proven to be an effective mechanism to enhance thermoelectric performance due primarily to a reduction in lattice thermal conductivity. Specifically, our findings on the series In x Yb y Co4Sb12 [0 ≤ (x, y) ≤ 0.2] have further motivated an attempt to form triple-filled skutterudites Ce0.1In x Yb y Co4Sb12 with
Eighteenth International Conference on Thermoelectrics. Proceedings, ICT'99 (Cat. No.99TH8407)
Filled skutterudite antimonides are an example of electron crystal and phonon-glass materials as ... more Filled skutterudite antimonides are an example of electron crystal and phonon-glass materials as originally proposed by Slack (1994). A properly optimized compound should exhibit high electrical conductivity and Seebeck coefficients in combination with a very low thermal conductivity, thus resulting in a high value for ZT. In skutterudites, the low thermal conductivity results from the incoherent rattling of the loosely
ABSTRACTCompounds with clathrate-hydrate type crystal lattice structures are currently of interes... more ABSTRACTCompounds with clathrate-hydrate type crystal lattice structures are currently of interest in thermoelectric materials research. This is due to the fact that semiconducting compounds can be synthesized with varying doping levels while possessing low, even ‘glass-like’, thermal conductivity. Up to now most of the work has focused on type I Si and Ge clathrates. Sn-clathrates however are viewed as having the greatest potential for thermoelectric cooling applications due to the larger mass of Sn and the expected small band-gap, as compared to Si and Ge clathrates. Transport properties on type I Sn-clathrates has only recently been reported [1–3]. In this report we present ongoing experimental research on both type I and II clathrates with an emphasis on the thermal transport of these novel materials. We present thermal conductivity data Si-Ge and Ge-Sn alloys as well as on a type II Ge clathrate for the first time, and compare these data to that of other clathrate compounds.
ABSTRACTThe pentatelluride materials (Hf1-XZrXTe5) have recently garnered much interest as a pote... more ABSTRACTThe pentatelluride materials (Hf1-XZrXTe5) have recently garnered much interest as a potential low temperature thermoelectric material. Their power factor exceeds that of the current Bi2Te3 materials over the temperature range 150 K < T < 350 K. A formidable challenge has been the capability of measuring the thermal conductivity of small needle-like samples (2.0 × 0.05 × 0.1 mm3) such as pentatellurides (HfXZr1-XTe5) due to heat loss and radiation effects. However in order to fully evaluate any material for potential thermoelectric use, the determination of the thermal conductivity of the material is necessary. We have recently developed a new technique called the parallel thermal conductance (PTC) technique to measure the thermal conductivity of such small samples. In this paper we describe the PTC method and measurements of the thermal conductivity of the pentatelluride materials will be presented for the first time. The potential of these materials for low temperatu...
ABSTRACTFilled skutterudite compounds possess very low thermal conductivities due to the scatteri... more ABSTRACTFilled skutterudite compounds possess very low thermal conductivities due to the scattering of a wide range of phonon modes caused by a loosely bound cation incorporated in a cavity of the structure. The inclusion of such a filler cation causes several synthetic difficulties since the desired compounds are thermodynamically unstable with respect to disproportionation. Modulated elemental reactants were used in this study to circumvent these difficulties. SnxCo4Sb12 samples with x=0.5 and nearly 1.0 were synthesized using this method. To prevent nucleation of unwanted binary compounds, the repeat unit made up of elemental layers was less than 20 angstroms 500mg of each sample were produced, allowing for the samples to be hot pressed into a pellet. Structural analysis as well as measurements of the physical properties are presented.
ABSTRACTThe skutterudite family of compounds continues to be of interest for thermoelectric appli... more ABSTRACTThe skutterudite family of compounds continues to be of interest for thermoelectric applications due to the low thermal conductivity obtained when filling the voids with small diameter, large mass interstitials such as trivalent rare-earth ions. In the last few years there has been a substantial experimental and theoretical effort in attempting to understand the transport properties of these compounds in order to optimize their thermoelectric properties. One such approach involves partially-filling the voids in attempting to optimize the power factor while maintaining low thermal conductivity. In this report experimental research on skutterudites with the voids partially filled with heavy mass lanthanide and alkaline-earth ions is reported.
Over the past decade, the open frame ("cagey") structure of CoSb 3 skutterudite has invited inten... more Over the past decade, the open frame ("cagey") structure of CoSb 3 skutterudite has invited intensive filling studies with various rare-earth elements for delivering state-of-theart mid-temperature thermoelectric performance. To rationalize previously reported experimental results and provide new insight into the underexplored roles of La fillers and Sb vacancies, ab initio density functional theory studies, along with semi-classical Boltzmann transport theory calculations, are performed for pristine CoSb 3 of different lattice settings and La-filled CoSb 3 with and without Sb's mono-and di-vacancy defects. The effects of spin-orbit coupling (SOC), partial La-filling, Sb vacancy defects, and spin polarization on the electronic and thermoelectric properties are systematically examined. The SOC shows minor effects on the electronic and thermoelectric properties of CoSb 3. The peculiar quasi-Dirac band in the pristine CoSb 3 largely survives La filling but not Sb vacancies, which instead introduce dispersive bands in the band gap region. The non-spin-polarized and spin-polarized solutions of La-filled CoSb 3 are nearly degenerate. Importantly, the band structure, density of states, and Fermi surface of the latter are significantly spin polarized, giving rise to spin-dependent thermoelectric properties. Seebeck coefficients directly calculated as a function of chemical potential are interpreted in connection with the electronic structures. Temperature-dependent Seebeck coefficients derived for the experimentally studied materials agree well with available experimental data. Seebeck coefficients obtained as a function of charge carrier concentration corroborate the thermoelectrically favorable role at high filling fractions played by the Fermi electron pockets associated with the degenerate valleys in the conduction bands, and also point toward a similar role of the Fermi hole pockets associated with the degenerate hills in the valence bands. These results serve to advance the understanding of CoSb 3 skutterudite, a class of materials with important fundamental and application implications for thermoelectrics and spintronics.
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Papers by Terry Tritt