Keshab Dahal - Academia.edu (original) (raw)

Papers by Keshab Dahal

Research paper thumbnail of Liドープp‐型Mg2(Ge,Sn)の熱電性能とMg2(Si,Sn)との比較

Research paper thumbnail of Thermoelectric properties of Li-doped Mg2(Ge,Sn) and Mg2(Si,Sn)

Research paper thumbnail of Solid-State Phase Change and Thermochemical Materials for Thermal Management

Research paper thumbnail of Highly efficient hydrogen evolution by self-standing nickel phosphide-based hybrid nanosheet arrays electrocatalyst

Research paper thumbnail of Deep defect level engineering: a strategy of optimizing the carrier concentration for high thermoelectric performance

Energy & Environmental Science

Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the o... more Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the optimization of carrier concentration plays a central role in achieving high thermoelectric performance.

Research paper thumbnail of Hierarchical CoP/Ni5P4/CoP microsheet arrays as a robust pH-universal electrocatalyst for efficient hydrogen generation

Energy & Environmental Science

Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni5... more Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni5P4/CoP microsheet arrays for pH-universal hydrogen evolution through simply wrapping Ni5P4 nanosheet arrays in CoP nanoparticles.

Research paper thumbnail of The effect of charge carrier and doping site on thermoelectric properties of Mg 2 Sn 0.75 Ge 0.25

Acta Materialia

Mg 2 Sn 0.75 Ge 0.25 has been recently demonstrated to be a promising thermoelectric material for... more Mg 2 Sn 0.75 Ge 0.25 has been recently demonstrated to be a promising thermoelectric material for power generation in the temperature range from room temperature to 723 K because of the high power factor of ~54 µW cm-1 K-2 upon Sb doping to the Sn site. The enhanced density of states effective mass and weak electron scattering from the alloying effect are believed to be the main reasons for the high power factor (PF) and hence high figure of merit (ZT). In this study, it is shown that the right choice of carrier donor also plays an important role in obtaining high power

Research paper thumbnail of Thermoelectric properties of n-type half-Heusler compounds (Hf 0.25 Zr 0.75 ) 1–x Nb x NiSn

Acta Materialia

A series of Nb doped (Hf0.25Zr0.75)1-xNbxNiSn (x = 0-0.03) samples were synthesized and studied b... more A series of Nb doped (Hf0.25Zr0.75)1-xNbxNiSn (x = 0-0.03) samples were synthesized and studied by arc-melting the elements to first form ingots, then ball-milling the ingots to obtain fine powders, and finally hot-pressing the fine powder to form bulk samples. Instead of the conventional Sb doping on the Sn site of the n-type half-Heusler, it was found that Nb is also an effective dopant. When the carrier concentration is optimized at 2.2% Nb, a power factor of ~47 μW cm-1 K-2 is achieved at and above 600 °C, and a peak ZT ~0.9 is achieved at 700 °C with Nb doping from 1.8 at% to 2.2 at%. An output power density of ~22 W cm-2 and a leg efficiency of ~12% are calculated for the Nb doped samples.

Research paper thumbnail of High thermoelectric performance of n-type PbTe 1−y S y due to deep lying states induced by indium doping and spinodal decomposition

Nano Energy

Good thermoelectric materials should have high engineering figure-of-merit (ZT) eng , not peak ZT... more Good thermoelectric materials should have high engineering figure-of-merit (ZT) eng , not peak ZT, to achieve high conversion efficiency. In this work, we achieved a good (ZT) eng by optimizing the carrier concentration to improve the room temperature ZT using deep lying dopant, indium, in PbTe 1-y S y. It was found that a room temperature ZT as high as ~0.5 and a peak ZT ~1.1 at about 673 K were obtained in Pb 0.98 In 0.02 Te 0.8 S 0.2 due to a lower thermal conductivity by alloy scattering and Spinodal decomposition. The calculated efficiency could be as high as ~12% at cold side 323 K and hot side 773 K. The approach is expected to work in other materials systems too.

Research paper thumbnail of Thermal conductivity of (VO2)1-xCux composites across the phase transition temperature

Journal of Applied Physics

Research paper thumbnail of V–VO2 core–shell structure for potential thermal switching

RSC Adv.

An increase in thermal conductivity is achieved by increasing electronic thermal conductivityviam... more An increase in thermal conductivity is achieved by increasing electronic thermal conductivityviamodulation doping, resulting from solid–solid phase transition.

Research paper thumbnail of Graphene Flakes: Orientation Control of Graphene Flakes by Magnetic Field: Broad Device Applications of Macroscopically Aligned Graphene (Adv. Mater. 1/2017)

Advanced Materials, 2017

Writing letters with a suspension of graphene flakes and a magnet bar: the suspension is initiall... more Writing letters with a suspension of graphene flakes and a magnet bar: the suspension is initially opaque due to randomly oriented graphene flakes, but the magnet's field makes it transparent by aligning the flakes. The graphene's diamagnetic and anisotropic absorptive properties make this writing board possible, as shown in article 1604453 by Z. M. Wang, J. M. Bao, and co-workers.

Research paper thumbnail of Orientation Control of Graphene Flakes by Magnetic Field: Broad Device Applications of Macroscopically Aligned Graphene

Advanced materials (Deerfield Beach, Fla.), 2017

Owing to a large diamagnetism, graphene flakes can respond and be aligned to magnetic field like ... more Owing to a large diamagnetism, graphene flakes can respond and be aligned to magnetic field like a ferromagnetic material. Aligned graphene flakes exhibit emergent properties approaching single-layer graphene. Anisotropic optical properties also give rise to a magnetic writing board using graphene suspension and a bar magnet as a pen. This simple alignment technique opens up enormous applications of graphene.

Research paper thumbnail of Transport and mechanical properties of the double-filled p-type skutterudites La0.68Ce0.22Fe4−xCoxSb12

Acta Materialia, 2016

Till date, the dimensionless figure of merit (ZT) of p-type skutterudites lags its n-type counter... more Till date, the dimensionless figure of merit (ZT) of p-type skutterudites lags its n-type counterpart. In this work, we report improved thermoelectric performance of La/Ce double filled p-type skutterudites. The samples were synthesized by hot pressing nano-powder made by ball milling annealed ingots of La 0.68 Ce 0.22 Fe 4-x Co x Sb 12 with varying Co concentration. By tuning the Fe/Co ratio, we achieved a higher power factor (~35 µW cm-1 K-2 at 475 o C), leading to a peak ZT of 1.15 at 475 o C in La 0.68 Ce 0.22 Fe 3.5 Co 0.5 Sb 12. Nanoindentation experiment carried on fine surface of the best sample reveals hardness of 5.4 GPa and modulus of elasticity of 126 GPa, which is much higher than those of Bi 2 Te 3 and PbTe based materials, indicating skutterudites are mechanically strong, good for some practical applications.

Research paper thumbnail of NbFeSb based p-type half-Heusler for power generation applications

Bulletin of the American Physical Society, Mar 3, 2015

We report a peak dimensionless figure-of-merit (ZT) of˜1 at 700 o C in nanostructured p-type Nb 0... more We report a peak dimensionless figure-of-merit (ZT) of˜1 at 700 o C in nanostructured p-type Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition. Even though the power factor of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition is improved by 25% in comparison to the previously reported p-type Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2 , the ZT value is not increased due to a higher thermal conductivity. However, the higher power factor of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition led to a 15% increase in power output of a thermoelectric device in comparison to a device made from the previous best material Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2. The n-type material used to make the unicouple device is the best reported nanostructured Hf 0.25 Zr 0.75 NiSn 0.99 Sb 0.01 composition with the lowest hafnium (Hf) content. Both the p-and n-type nanostructured samples are prepared by ball milling the arc melted ingot and hot pressing the finely ground powders. Moreover, the raw material cost of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition is more than six times lower compared to the cost of the previous best p-type Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2. This cost reduction is crucial for these materials to be used in large-scale quantities for vehicle and industrial waste heat recovery applications.

Research paper thumbnail of Studies on thermoelectric figure of merit of Na-doped p-type polycrystalline SnSe

J. Mater. Chem. A, 2016

Na doping improved both the peak and average ZT of p-type polycrystalline SnSe.

Research paper thumbnail of High thermoelectric power factor in Cu–Ni alloy originate from potential barrier scattering of twin boundaries

Nano Energy, 2015

Constantan alloy (Cu-Ni) has beenknown for a long time in thermocouplesdue to itsthermal power pr... more Constantan alloy (Cu-Ni) has beenknown for a long time in thermocouplesdue to itsthermal power property. In this study, we show an enhancementin thermoelectric performance of Cu 56 Ni 42 Mn 2 alloy by introducingnanoscale twins into its microstructure. Comparing to arc-melted ingot (without nanoscale twins), the ball milled and hot pressed (BM-HP) samples with twinning showed a higher Seebeck coefficient of ~-72.5 μV K-1 (an increase of ~12% at 873 K),a larger power factor of ~102 μW cm-1 K-2 (an increase of ~21% at 873 K), and hence a higher ZT of ~0.19 (an increase of ~34% at 873 K). A high output power density of ~53.4 W cm-2 is calculated from the high power factor even though the conversion efficiency is lower than 3% due to the low ZT. TEM characterization showsthere isa large quantity ofnanoscale twins with spacing of 50 to 200 nm. It is very likelythat low-energycarriers are selectively scattered by the twin boundaries (i.e., potential barrier scattering) thus lead to enhanced Seebeck coefficient. The improved thermoelectric performance of nano-twinned Cu-Ni alloy suggests constantan could be promising in thermoelectric power

Research paper thumbnail of A new n-type half-Heusler thermoelectric material NbCoSb

Materials Research Bulletin, 2015

We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure... more We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure having valence electron count of 19, different from the traditional 18, which opens up a new route to develop new half-Heusler thermoelectric materials not following the traditional valence electron count of 18. The samples are made by arc melting followed by ball milling and hot pressing. The effect of hot pressing temperature on the thermoelectric properties of NbCoSb samples has been studied. A maximum thermoelectric figure-of-merit (ZT) of ~0.4 is achieved at 700 °C in NbCoSb sample that is hot pressed at 1000 °C. This work add a new member to HH compounds for thermoelectric applications, although the peak ZT of ~0.4 is still lower than that of the traditional HHs. Moreover, it is very interesting to see that a traditionally thought of valence electron counts of 18 is not required.

Research paper thumbnail of Studies on Thermoelectric Properties of n-type Polycrystalline SnSe 1- x S x by Iodine Doping

Advanced Energy Materials, 2015

We prepared iodine-doped n-type SnSe polycrystalline by melting and hot pressing. The prepared ma... more We prepared iodine-doped n-type SnSe polycrystalline by melting and hot pressing. The prepared material is anisotropic with a peak ZT of ~0.8 at about 773 K measured along the hot pressing direction. This is the first report on TE properties of n-type Sn chalcogenide alloys. With increasing content of iodine, the carrier concentration changed from 2.3×10 17 cm-3 (p-type) to 5.0×10 15 cm-3 (n-type) then to 2.0×10 17 cm-3 (n-type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p-type SnSe. By alloying with 10 atm. % SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ~1.0 at about 773 K measured also along the hot pressing direction.

Research paper thumbnail of Effect of triple fillers in thermoelectric performance of p-type skutterudites

Journal of Alloys and Compounds, 2015

Up-to-date, the thermoelectric performance of p-type skutterudites lags that of the corresponding... more Up-to-date, the thermoelectric performance of p-type skutterudites lags that of the corresponding n-type materials. In this work, we report improved thermoelectric performance of p-type skutterudites by triple filling the voids. The samples were synthesized by hot pressing nanopowder made by ball milling the annealed ingots of Ca x Ce 0.35 Nd 0.35 Fe 4-y Co y Sb 12 with varying concentration of x and y. By tuning the filler concentration and Fe/Co ratio, we achieved a lower thermal conductivity (~2.0 W m-1 K-1 at room temperature and ~2.6 W m-1 K-1 at 535 o C) and a higher power factor (~35 µW cm-1 K-2 at 475 o C), leading to a peak ZT of about 1.1 at 475 o C. The observed lower thermal conductivity can be attributed to a broad range of phonon scattering due to multiple fillers and the enhanced mobility due to the light element Ca leading to a high power factor.

Research paper thumbnail of Liドープp‐型Mg2(Ge,Sn)の熱電性能とMg2(Si,Sn)との比較

Research paper thumbnail of Thermoelectric properties of Li-doped Mg2(Ge,Sn) and Mg2(Si,Sn)

Research paper thumbnail of Solid-State Phase Change and Thermochemical Materials for Thermal Management

Research paper thumbnail of Highly efficient hydrogen evolution by self-standing nickel phosphide-based hybrid nanosheet arrays electrocatalyst

Research paper thumbnail of Deep defect level engineering: a strategy of optimizing the carrier concentration for high thermoelectric performance

Energy & Environmental Science

Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the o... more Thermoelectric properties are heavily dependent on the carrier concentration, and therefore the optimization of carrier concentration plays a central role in achieving high thermoelectric performance.

Research paper thumbnail of Hierarchical CoP/Ni5P4/CoP microsheet arrays as a robust pH-universal electrocatalyst for efficient hydrogen generation

Energy & Environmental Science

Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni5... more Exceptional Pt-like electrocatalytic activity was achieved in a sandwich-like catalyst of CoP/Ni5P4/CoP microsheet arrays for pH-universal hydrogen evolution through simply wrapping Ni5P4 nanosheet arrays in CoP nanoparticles.

Research paper thumbnail of The effect of charge carrier and doping site on thermoelectric properties of Mg 2 Sn 0.75 Ge 0.25

Acta Materialia

Mg 2 Sn 0.75 Ge 0.25 has been recently demonstrated to be a promising thermoelectric material for... more Mg 2 Sn 0.75 Ge 0.25 has been recently demonstrated to be a promising thermoelectric material for power generation in the temperature range from room temperature to 723 K because of the high power factor of ~54 µW cm-1 K-2 upon Sb doping to the Sn site. The enhanced density of states effective mass and weak electron scattering from the alloying effect are believed to be the main reasons for the high power factor (PF) and hence high figure of merit (ZT). In this study, it is shown that the right choice of carrier donor also plays an important role in obtaining high power

Research paper thumbnail of Thermoelectric properties of n-type half-Heusler compounds (Hf 0.25 Zr 0.75 ) 1–x Nb x NiSn

Acta Materialia

A series of Nb doped (Hf0.25Zr0.75)1-xNbxNiSn (x = 0-0.03) samples were synthesized and studied b... more A series of Nb doped (Hf0.25Zr0.75)1-xNbxNiSn (x = 0-0.03) samples were synthesized and studied by arc-melting the elements to first form ingots, then ball-milling the ingots to obtain fine powders, and finally hot-pressing the fine powder to form bulk samples. Instead of the conventional Sb doping on the Sn site of the n-type half-Heusler, it was found that Nb is also an effective dopant. When the carrier concentration is optimized at 2.2% Nb, a power factor of ~47 μW cm-1 K-2 is achieved at and above 600 °C, and a peak ZT ~0.9 is achieved at 700 °C with Nb doping from 1.8 at% to 2.2 at%. An output power density of ~22 W cm-2 and a leg efficiency of ~12% are calculated for the Nb doped samples.

Research paper thumbnail of High thermoelectric performance of n-type PbTe 1−y S y due to deep lying states induced by indium doping and spinodal decomposition

Nano Energy

Good thermoelectric materials should have high engineering figure-of-merit (ZT) eng , not peak ZT... more Good thermoelectric materials should have high engineering figure-of-merit (ZT) eng , not peak ZT, to achieve high conversion efficiency. In this work, we achieved a good (ZT) eng by optimizing the carrier concentration to improve the room temperature ZT using deep lying dopant, indium, in PbTe 1-y S y. It was found that a room temperature ZT as high as ~0.5 and a peak ZT ~1.1 at about 673 K were obtained in Pb 0.98 In 0.02 Te 0.8 S 0.2 due to a lower thermal conductivity by alloy scattering and Spinodal decomposition. The calculated efficiency could be as high as ~12% at cold side 323 K and hot side 773 K. The approach is expected to work in other materials systems too.

Research paper thumbnail of Thermal conductivity of (VO2)1-xCux composites across the phase transition temperature

Journal of Applied Physics

Research paper thumbnail of V–VO2 core–shell structure for potential thermal switching

RSC Adv.

An increase in thermal conductivity is achieved by increasing electronic thermal conductivityviam... more An increase in thermal conductivity is achieved by increasing electronic thermal conductivityviamodulation doping, resulting from solid–solid phase transition.

Research paper thumbnail of Graphene Flakes: Orientation Control of Graphene Flakes by Magnetic Field: Broad Device Applications of Macroscopically Aligned Graphene (Adv. Mater. 1/2017)

Advanced Materials, 2017

Writing letters with a suspension of graphene flakes and a magnet bar: the suspension is initiall... more Writing letters with a suspension of graphene flakes and a magnet bar: the suspension is initially opaque due to randomly oriented graphene flakes, but the magnet's field makes it transparent by aligning the flakes. The graphene's diamagnetic and anisotropic absorptive properties make this writing board possible, as shown in article 1604453 by Z. M. Wang, J. M. Bao, and co-workers.

Research paper thumbnail of Orientation Control of Graphene Flakes by Magnetic Field: Broad Device Applications of Macroscopically Aligned Graphene

Advanced materials (Deerfield Beach, Fla.), 2017

Owing to a large diamagnetism, graphene flakes can respond and be aligned to magnetic field like ... more Owing to a large diamagnetism, graphene flakes can respond and be aligned to magnetic field like a ferromagnetic material. Aligned graphene flakes exhibit emergent properties approaching single-layer graphene. Anisotropic optical properties also give rise to a magnetic writing board using graphene suspension and a bar magnet as a pen. This simple alignment technique opens up enormous applications of graphene.

Research paper thumbnail of Transport and mechanical properties of the double-filled p-type skutterudites La0.68Ce0.22Fe4−xCoxSb12

Acta Materialia, 2016

Till date, the dimensionless figure of merit (ZT) of p-type skutterudites lags its n-type counter... more Till date, the dimensionless figure of merit (ZT) of p-type skutterudites lags its n-type counterpart. In this work, we report improved thermoelectric performance of La/Ce double filled p-type skutterudites. The samples were synthesized by hot pressing nano-powder made by ball milling annealed ingots of La 0.68 Ce 0.22 Fe 4-x Co x Sb 12 with varying Co concentration. By tuning the Fe/Co ratio, we achieved a higher power factor (~35 µW cm-1 K-2 at 475 o C), leading to a peak ZT of 1.15 at 475 o C in La 0.68 Ce 0.22 Fe 3.5 Co 0.5 Sb 12. Nanoindentation experiment carried on fine surface of the best sample reveals hardness of 5.4 GPa and modulus of elasticity of 126 GPa, which is much higher than those of Bi 2 Te 3 and PbTe based materials, indicating skutterudites are mechanically strong, good for some practical applications.

Research paper thumbnail of NbFeSb based p-type half-Heusler for power generation applications

Bulletin of the American Physical Society, Mar 3, 2015

We report a peak dimensionless figure-of-merit (ZT) of˜1 at 700 o C in nanostructured p-type Nb 0... more We report a peak dimensionless figure-of-merit (ZT) of˜1 at 700 o C in nanostructured p-type Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition. Even though the power factor of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition is improved by 25% in comparison to the previously reported p-type Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2 , the ZT value is not increased due to a higher thermal conductivity. However, the higher power factor of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition led to a 15% increase in power output of a thermoelectric device in comparison to a device made from the previous best material Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2. The n-type material used to make the unicouple device is the best reported nanostructured Hf 0.25 Zr 0.75 NiSn 0.99 Sb 0.01 composition with the lowest hafnium (Hf) content. Both the p-and n-type nanostructured samples are prepared by ball milling the arc melted ingot and hot pressing the finely ground powders. Moreover, the raw material cost of the Nb 0.6 Ti 0.4 FeSb 0.95 Sn 0.05 composition is more than six times lower compared to the cost of the previous best p-type Hf 0.44 Zr 0.44 Ti 0.12 CoSb 0.8 Sn 0.2. This cost reduction is crucial for these materials to be used in large-scale quantities for vehicle and industrial waste heat recovery applications.

Research paper thumbnail of Studies on thermoelectric figure of merit of Na-doped p-type polycrystalline SnSe

J. Mater. Chem. A, 2016

Na doping improved both the peak and average ZT of p-type polycrystalline SnSe.

Research paper thumbnail of High thermoelectric power factor in Cu–Ni alloy originate from potential barrier scattering of twin boundaries

Nano Energy, 2015

Constantan alloy (Cu-Ni) has beenknown for a long time in thermocouplesdue to itsthermal power pr... more Constantan alloy (Cu-Ni) has beenknown for a long time in thermocouplesdue to itsthermal power property. In this study, we show an enhancementin thermoelectric performance of Cu 56 Ni 42 Mn 2 alloy by introducingnanoscale twins into its microstructure. Comparing to arc-melted ingot (without nanoscale twins), the ball milled and hot pressed (BM-HP) samples with twinning showed a higher Seebeck coefficient of ~-72.5 μV K-1 (an increase of ~12% at 873 K),a larger power factor of ~102 μW cm-1 K-2 (an increase of ~21% at 873 K), and hence a higher ZT of ~0.19 (an increase of ~34% at 873 K). A high output power density of ~53.4 W cm-2 is calculated from the high power factor even though the conversion efficiency is lower than 3% due to the low ZT. TEM characterization showsthere isa large quantity ofnanoscale twins with spacing of 50 to 200 nm. It is very likelythat low-energycarriers are selectively scattered by the twin boundaries (i.e., potential barrier scattering) thus lead to enhanced Seebeck coefficient. The improved thermoelectric performance of nano-twinned Cu-Ni alloy suggests constantan could be promising in thermoelectric power

Research paper thumbnail of A new n-type half-Heusler thermoelectric material NbCoSb

Materials Research Bulletin, 2015

We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure... more We surprisingly made a new n-type thermoelectric compound NbCoSb with half-Heusler (HH) structure having valence electron count of 19, different from the traditional 18, which opens up a new route to develop new half-Heusler thermoelectric materials not following the traditional valence electron count of 18. The samples are made by arc melting followed by ball milling and hot pressing. The effect of hot pressing temperature on the thermoelectric properties of NbCoSb samples has been studied. A maximum thermoelectric figure-of-merit (ZT) of ~0.4 is achieved at 700 °C in NbCoSb sample that is hot pressed at 1000 °C. This work add a new member to HH compounds for thermoelectric applications, although the peak ZT of ~0.4 is still lower than that of the traditional HHs. Moreover, it is very interesting to see that a traditionally thought of valence electron counts of 18 is not required.

Research paper thumbnail of Studies on Thermoelectric Properties of n-type Polycrystalline SnSe 1- x S x by Iodine Doping

Advanced Energy Materials, 2015

We prepared iodine-doped n-type SnSe polycrystalline by melting and hot pressing. The prepared ma... more We prepared iodine-doped n-type SnSe polycrystalline by melting and hot pressing. The prepared material is anisotropic with a peak ZT of ~0.8 at about 773 K measured along the hot pressing direction. This is the first report on TE properties of n-type Sn chalcogenide alloys. With increasing content of iodine, the carrier concentration changed from 2.3×10 17 cm-3 (p-type) to 5.0×10 15 cm-3 (n-type) then to 2.0×10 17 cm-3 (n-type). The decent ZT is mainly attributed to the intrinsically low thermal conductivity due to the high anharmonicity of the chemical bonds like those in p-type SnSe. By alloying with 10 atm. % SnS, even lower thermal conductivity and an enhanced Seebeck coefficient were achieved, leading to an increased ZT of ~1.0 at about 773 K measured also along the hot pressing direction.

Research paper thumbnail of Effect of triple fillers in thermoelectric performance of p-type skutterudites

Journal of Alloys and Compounds, 2015

Up-to-date, the thermoelectric performance of p-type skutterudites lags that of the corresponding... more Up-to-date, the thermoelectric performance of p-type skutterudites lags that of the corresponding n-type materials. In this work, we report improved thermoelectric performance of p-type skutterudites by triple filling the voids. The samples were synthesized by hot pressing nanopowder made by ball milling the annealed ingots of Ca x Ce 0.35 Nd 0.35 Fe 4-y Co y Sb 12 with varying concentration of x and y. By tuning the filler concentration and Fe/Co ratio, we achieved a lower thermal conductivity (~2.0 W m-1 K-1 at room temperature and ~2.6 W m-1 K-1 at 535 o C) and a higher power factor (~35 µW cm-1 K-2 at 475 o C), leading to a peak ZT of about 1.1 at 475 o C. The observed lower thermal conductivity can be attributed to a broad range of phonon scattering due to multiple fillers and the enhanced mobility due to the light element Ca leading to a high power factor.