In recent years the emerge of high-entropy alloys (HEAs) imposes an evolution in metallic materia... more In recent years the emerge of high-entropy alloys (HEAs) imposes an evolution in metallic materials, which breaks the boundaries set by the traditional alloys. Alongside the development of HEAs, the medium-entropy alloys (MEAs), which comprise two to four majority elements, also reveal the outperforming properties with less compositional complexity. Among them, the medium-entropy AlNbV alloys attract great attention owing to the existence of a body-centered cubic (BCC) solid solution that contains soluble Al, Nb, and V elements. Herein, we construct the phase diagrams for the Al-Nb-V system and define the equilibrium homogeneity by thermally-equilibrated ternary alloys underwent a post-annealing at 1073 K or 1273 K. Meanwhile, a superposition of phase diagram and thermal conductivity κ mapping suggests that the coexistence of BCC solid solution and nano-grained AlNb2 brings down the κ. With the incorporation of Ti and Cr, the HEA AlNbVCrTi, which is composed of Laves C14 phase and BCC solid solution, achieves an ultralow κ of 6 – 10 Wm-1K-1 within 323 – 723 K.
(Taiwan) and started his academic carrier at the institute of physics, Academia Sinica (Taiwan) i... more (Taiwan) and started his academic carrier at the institute of physics, Academia Sinica (Taiwan) in 2011. His research interests include molecular beam epitaxy of III-V semiconductors, single-crystal growth, lattice dynamics of low-thermal-conductivity materials, and thermoelectric materials.
Zn4Sb3-based compounds constitute a lead-free material family with a best thermoelectric figure o... more Zn4Sb3-based compounds constitute a lead-free material family with a best thermoelectric figure of merit (zT) in the midtemperature range. Unlike being a stoichiometric compound, the mutual solubility of Zn and Sb elicits rich microstructures and the structural instability of Zn4Sb3. The solubility limit and neighboring phase relations are crucial for the delicate balance between the thermoelectric performance and phase stability of Zn4Sb3. In this work, we constructed the isothermal section of the Zn–Sb–In ternary phase diagram, built the zT map near the β-Zn4Sb3 phase region, and showed that the formation of multiscale microstructures has a profound impact on the electronic and phonon transport properties and phase stability. A high-zT zone was identified near the phase boundary between the two-phase InSb + Zn5Sb4In2 and the three-phase Zn4Sb3 + InSb + Zn5Sb4In2 regions. A sample with a nominal composition of Zn3.8In0.2Sb3 exhibited an ultralow κL of 0.2 (W m–1 K–1), an enhanced PF of 1.75 (mW m–1 K–2),...
Abstract Hydrogen evolution reaction (HER) from water electrolysis is a promising route for hydro... more Abstract Hydrogen evolution reaction (HER) from water electrolysis is a promising route for hydrogen fuel production. However, an effective conversion technology from distributed energy resources, such as solar energy and thermal energy, to hydrogen energy is still a challenging research. Here, earth-abundant and multifunctional Ni nanosheets array as electrocatalysts and light absorption layer integrated thermoelectric (TE) device for overall water splitting was proposed. Instead of the traditional power source, the output voltage from thermoelectric (TE) device was directly used for water splitting. More importantly, the structural, photothermal transformation and electrocatalytic characterizations confirmed that the earth-abundant and multifunctional Ni nanosheets array grown on the hot side of TE device was not only as an efficient photothermal conversion layer for providing temperature difference (ΔT) of TE, but also as an active electrocatalysts for HER. The Electrolyzer-TE hybrid devices were designed for overall water splitting in a two-electrode configuration, which possessed high hydrogen production rate of 1.818 mmol/h and oxygen production rate of 0.912 mmol/h. The proposed integrative TE device herein offered great advantages in terms of designing the overall water splitting system, which are helpful for its practical applications for utilization of solar thermal and waste heat.
Abstract Among all types of thermoelectric materials, chalcopyrite CuGaTe 2 has been viewed as a ... more Abstract Among all types of thermoelectric materials, chalcopyrite CuGaTe 2 has been viewed as a promising candidate for use of thermoelectric generator due to its high figure-of-merit ( zT ) at the high temperatures. Herein the 923 K isothermal section of ternary Cu-Ga-Te system is determined, using various thermally-equilibrated Cu-Ga-Te alloys, and ternary CuGaTe 2 phase is stabilized within the compositional region of 48.0–53.0 at%Te and 25.0 at%-30.0 at%Cu. Moreover, the solubility of Cu in binary Ga 2 Te 3 and Ga 3 Te 4 compounds at 923 K is negligible, while that in GaTe phase reaches 7.9 at%Cu. The as-determined isothermal section, depicting the phase stability regime of CuGaTe 2 , provides options for precisely locating the compositions of CuGaTe 2 -based materials that lead to promising and reproducible thermoelectric properties. A zT peak of 0.6 has been achieved in the Bridgman-grown Cu 25 Ga 26 Te 49 alloy at 750 K, which is nearly eight times higher than the neighboring Cu 28 Ga 25 Te 47 alloy, presumably due to the fact that the Cu 25 Ga 26 Te 49 alloy, which exhibits high phase purity of CuGaTe 2 , has lower lattice thermal conductivity (κ L ∼1.3 (W/mK) and higher power factor ( PF ∼11.2 (μW/mK 2 )), comparing with that of Cu 28 Ga 25 Te 47 alloy (κ L ∼1.8 (W/mK) and PF ∼1.9 (μW/mK 2 )), which locates in a three-phased CuGaTe 2 +Cu 2 Te + Cu 9 Ga 4 region, with only a slight deviation in the starting composition.
A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequi... more A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequiatiomic approach and alloys were produced through arc melting and drop casting. These alloys comprised a body-centered cubic (BCC) and face-centered cubic (FCC) dual phase with a density of approximately 4.5 g/cm3. However, the fraction of the BCC phase and morphology of the FCC phase can be controlled by incorporating other elements. The results of compression tests indicated that these Al-Ti-Cr-Mn-V alloys exhibited a prominent compression strength (~1940 MPa) and ductility (~30%). Moreover, homogenized samples maintained a high compression strength of 1900 MPa and similar ductility (30%). Due to the high specific compressive strength (0.433 GPa·g/cm3) and excellent combination of strength and ductility, the cast lightweight Al-Ti-Cr-Mn-V MEAs are a promising alloy system for application in transportation and energy industries.
Engineering transport properties of thermoelectric (TE) materials leads to incessantly breakthrou... more Engineering transport properties of thermoelectric (TE) materials leads to incessantly breakthroughs in the zT values. Nevertheless, modular design holds a key factor to advance the TE technology. Herein, we discuss the structures of TE module and illustrate the inter-diffusions across the interface of constituent layers. For Bi 2 Te 3-based module, soldering is the primary bonding method, giving rise to the investigations on the selections of solder, diffusion barrier layer and electrode. For midtemperature PbTe-based TE module, hot-pressing or spark plasma sintering are alternative bonding approaches; the inter-diffusions between the diffusion barrier layer, electrode and TE substrate are addressed as well.
The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdi... more The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe 2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8-360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick's second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10 −20-10 −23 (m 2 /s), which is 10 6~1 0 7 and 10 12~1 0 13 times smaller than those of Ni [10 −14-10 −17 (m 2 /s)] and Cu [10 −8-10 −11 (m 2 /s)] in Bi 2 Te 3 , respectively.
The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe-... more The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe-Ag 2 Te-Sb 2 Te 3 system were examined using samples that were compositionally graded by unidirectional solidification by the Bridgman method and diffusion couples. At compositions near the middle of the pseudo-binary PbTe-AgSbTe 2 line, a compositionally modulated microstructure has been found. From diffusion couple experiments, it is found that the PbTe-AgSbTe 2 system exhibits a miscibility gap at low temperatures while it forms a complete solid solution at high temperatures; the critical temperature is between 400 C and 450 C. The modulated microstructure originates from the decomposition of the high-temperature solid solution during cooling. Scanning Seebeck coefficient measurement on these samples covers a wide compositional space of the pseudo-ternary system. The Seebeck coefficient transitions from positive values at AgSbTe 2 -rich compositions to negative values at PbTe-rich compositions on the pseudo-binary PbTe-AgSbTe 2 line. Composition-graded samples prepared by the Bridgman method are thus useful to investigate thermoelectric materials in multicomponent systems.
Regular arrays of nano-wire microstructures containing Ag 2 Te rods with diameter <400 nm and int... more Regular arrays of nano-wire microstructures containing Ag 2 Te rods with diameter <400 nm and inter-rod distance <1 lm are formed in a matrix of AgSbTe 2 + d-Sb 2 Te, which makes an ordered nano-wire composite thermoelectric material. This microstructure is formed during eutectic solidification processing. To understand and guide production of uniform bulk samples of this composite, the liquidus projection of quaternary Pb-Ag-Sb-Te system at 36.0 at.% Te isoplethal section is constructed experimentally, using quenched samples. A three-phase univariant reaction of the quaternary Pb-Ag-Sb-Te system, L ! AgSbTe 2 +Ag 2 Te + d-Sb 2 Te, is investigated, between a ternary-eutectic melt (Ag-40.0 at.% Sb-36.0 at.% Te) and a quaternary melt (Pb-22.0 at.% Ag-40.0 at.% Sb-36.0 at.% Te), at 496.1°C and 503.9°C, respectively. High-resolution transmission electron microscopy confirms that these three phases are simultaneously present at the nanometer scale. Furthermore, unidirectional solidification experiments of the ternary eutectic alloy using the Bridgman method are carried out to examine the alloy's solidification behavior.
In recent years the emerge of high-entropy alloys (HEAs) imposes an evolution in metallic materia... more In recent years the emerge of high-entropy alloys (HEAs) imposes an evolution in metallic materials, which breaks the boundaries set by the traditional alloys. Alongside the development of HEAs, the medium-entropy alloys (MEAs), which comprise two to four majority elements, also reveal the outperforming properties with less compositional complexity. Among them, the medium-entropy AlNbV alloys attract great attention owing to the existence of a body-centered cubic (BCC) solid solution that contains soluble Al, Nb, and V elements. Herein, we construct the phase diagrams for the Al-Nb-V system and define the equilibrium homogeneity by thermally-equilibrated ternary alloys underwent a post-annealing at 1073 K or 1273 K. Meanwhile, a superposition of phase diagram and thermal conductivity κ mapping suggests that the coexistence of BCC solid solution and nano-grained AlNb2 brings down the κ. With the incorporation of Ti and Cr, the HEA AlNbVCrTi, which is composed of Laves C14 phase and BCC solid solution, achieves an ultralow κ of 6 – 10 Wm-1K-1 within 323 – 723 K.
(Taiwan) and started his academic carrier at the institute of physics, Academia Sinica (Taiwan) i... more (Taiwan) and started his academic carrier at the institute of physics, Academia Sinica (Taiwan) in 2011. His research interests include molecular beam epitaxy of III-V semiconductors, single-crystal growth, lattice dynamics of low-thermal-conductivity materials, and thermoelectric materials.
Zn4Sb3-based compounds constitute a lead-free material family with a best thermoelectric figure o... more Zn4Sb3-based compounds constitute a lead-free material family with a best thermoelectric figure of merit (zT) in the midtemperature range. Unlike being a stoichiometric compound, the mutual solubility of Zn and Sb elicits rich microstructures and the structural instability of Zn4Sb3. The solubility limit and neighboring phase relations are crucial for the delicate balance between the thermoelectric performance and phase stability of Zn4Sb3. In this work, we constructed the isothermal section of the Zn–Sb–In ternary phase diagram, built the zT map near the β-Zn4Sb3 phase region, and showed that the formation of multiscale microstructures has a profound impact on the electronic and phonon transport properties and phase stability. A high-zT zone was identified near the phase boundary between the two-phase InSb + Zn5Sb4In2 and the three-phase Zn4Sb3 + InSb + Zn5Sb4In2 regions. A sample with a nominal composition of Zn3.8In0.2Sb3 exhibited an ultralow κL of 0.2 (W m–1 K–1), an enhanced PF of 1.75 (mW m–1 K–2),...
Abstract Hydrogen evolution reaction (HER) from water electrolysis is a promising route for hydro... more Abstract Hydrogen evolution reaction (HER) from water electrolysis is a promising route for hydrogen fuel production. However, an effective conversion technology from distributed energy resources, such as solar energy and thermal energy, to hydrogen energy is still a challenging research. Here, earth-abundant and multifunctional Ni nanosheets array as electrocatalysts and light absorption layer integrated thermoelectric (TE) device for overall water splitting was proposed. Instead of the traditional power source, the output voltage from thermoelectric (TE) device was directly used for water splitting. More importantly, the structural, photothermal transformation and electrocatalytic characterizations confirmed that the earth-abundant and multifunctional Ni nanosheets array grown on the hot side of TE device was not only as an efficient photothermal conversion layer for providing temperature difference (ΔT) of TE, but also as an active electrocatalysts for HER. The Electrolyzer-TE hybrid devices were designed for overall water splitting in a two-electrode configuration, which possessed high hydrogen production rate of 1.818 mmol/h and oxygen production rate of 0.912 mmol/h. The proposed integrative TE device herein offered great advantages in terms of designing the overall water splitting system, which are helpful for its practical applications for utilization of solar thermal and waste heat.
Abstract Among all types of thermoelectric materials, chalcopyrite CuGaTe 2 has been viewed as a ... more Abstract Among all types of thermoelectric materials, chalcopyrite CuGaTe 2 has been viewed as a promising candidate for use of thermoelectric generator due to its high figure-of-merit ( zT ) at the high temperatures. Herein the 923 K isothermal section of ternary Cu-Ga-Te system is determined, using various thermally-equilibrated Cu-Ga-Te alloys, and ternary CuGaTe 2 phase is stabilized within the compositional region of 48.0–53.0 at%Te and 25.0 at%-30.0 at%Cu. Moreover, the solubility of Cu in binary Ga 2 Te 3 and Ga 3 Te 4 compounds at 923 K is negligible, while that in GaTe phase reaches 7.9 at%Cu. The as-determined isothermal section, depicting the phase stability regime of CuGaTe 2 , provides options for precisely locating the compositions of CuGaTe 2 -based materials that lead to promising and reproducible thermoelectric properties. A zT peak of 0.6 has been achieved in the Bridgman-grown Cu 25 Ga 26 Te 49 alloy at 750 K, which is nearly eight times higher than the neighboring Cu 28 Ga 25 Te 47 alloy, presumably due to the fact that the Cu 25 Ga 26 Te 49 alloy, which exhibits high phase purity of CuGaTe 2 , has lower lattice thermal conductivity (κ L ∼1.3 (W/mK) and higher power factor ( PF ∼11.2 (μW/mK 2 )), comparing with that of Cu 28 Ga 25 Te 47 alloy (κ L ∼1.8 (W/mK) and PF ∼1.9 (μW/mK 2 )), which locates in a three-phased CuGaTe 2 +Cu 2 Te + Cu 9 Ga 4 region, with only a slight deviation in the starting composition.
A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequi... more A novel lightweight Al-Ti-Cr-Mn-V medium-entropy alloy (MEA) system was developed using a nonequiatiomic approach and alloys were produced through arc melting and drop casting. These alloys comprised a body-centered cubic (BCC) and face-centered cubic (FCC) dual phase with a density of approximately 4.5 g/cm3. However, the fraction of the BCC phase and morphology of the FCC phase can be controlled by incorporating other elements. The results of compression tests indicated that these Al-Ti-Cr-Mn-V alloys exhibited a prominent compression strength (~1940 MPa) and ductility (~30%). Moreover, homogenized samples maintained a high compression strength of 1900 MPa and similar ductility (30%). Due to the high specific compressive strength (0.433 GPa·g/cm3) and excellent combination of strength and ductility, the cast lightweight Al-Ti-Cr-Mn-V MEAs are a promising alloy system for application in transportation and energy industries.
Engineering transport properties of thermoelectric (TE) materials leads to incessantly breakthrou... more Engineering transport properties of thermoelectric (TE) materials leads to incessantly breakthroughs in the zT values. Nevertheless, modular design holds a key factor to advance the TE technology. Herein, we discuss the structures of TE module and illustrate the inter-diffusions across the interface of constituent layers. For Bi 2 Te 3-based module, soldering is the primary bonding method, giving rise to the investigations on the selections of solder, diffusion barrier layer and electrode. For midtemperature PbTe-based TE module, hot-pressing or spark plasma sintering are alternative bonding approaches; the inter-diffusions between the diffusion barrier layer, electrode and TE substrate are addressed as well.
The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdi... more The thermal stability of joints in thermoelectric (TE) modules, which are degraded during interdiffusion between the TE material and the contacting metal, needs to be addressed in order to utilize TE technology for competitive, sustainable energy applications. Herein, we deposit a 200 nm-thick Zr-based thin-film metallic glass (TFMG), which acts as an effective diffusion barrier layer with low electrical contact resistivity, on a high-zT Se-doped AgSbTe 2 substrate. The reaction couples structured with TFMG/TE are annealed at 673 K for 8-360 hours and analyzed by electron microscopy. No observable IMCs (intermetallic compounds) are formed at the TFMG/TE interface, suggesting the effective inhibition of atomic diffusion that may be attributed to the grain-boundary-free structure of TFMG. The minor amount of Se acts as a tracer species, and a homogeneous Se-rich region is found nearing the TFMG/TE interface, which guarantees satisfactory bonding at the joint. The diffusion of Se, which has the smallest atomic volume of all the elements from the TE substrate, is found to follow Fick's second law. The calculated diffusivity (D) of Se in TFMG falls in the range of D~10 −20-10 −23 (m 2 /s), which is 10 6~1 0 7 and 10 12~1 0 13 times smaller than those of Ni [10 −14-10 −17 (m 2 /s)] and Cu [10 −8-10 −11 (m 2 /s)] in Bi 2 Te 3 , respectively.
The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe-... more The microstructures and Seebeck coefficients of thermoelectric alloys in the pseudo-ternary PbTe-Ag 2 Te-Sb 2 Te 3 system were examined using samples that were compositionally graded by unidirectional solidification by the Bridgman method and diffusion couples. At compositions near the middle of the pseudo-binary PbTe-AgSbTe 2 line, a compositionally modulated microstructure has been found. From diffusion couple experiments, it is found that the PbTe-AgSbTe 2 system exhibits a miscibility gap at low temperatures while it forms a complete solid solution at high temperatures; the critical temperature is between 400 C and 450 C. The modulated microstructure originates from the decomposition of the high-temperature solid solution during cooling. Scanning Seebeck coefficient measurement on these samples covers a wide compositional space of the pseudo-ternary system. The Seebeck coefficient transitions from positive values at AgSbTe 2 -rich compositions to negative values at PbTe-rich compositions on the pseudo-binary PbTe-AgSbTe 2 line. Composition-graded samples prepared by the Bridgman method are thus useful to investigate thermoelectric materials in multicomponent systems.
Regular arrays of nano-wire microstructures containing Ag 2 Te rods with diameter <400 nm and int... more Regular arrays of nano-wire microstructures containing Ag 2 Te rods with diameter <400 nm and inter-rod distance <1 lm are formed in a matrix of AgSbTe 2 + d-Sb 2 Te, which makes an ordered nano-wire composite thermoelectric material. This microstructure is formed during eutectic solidification processing. To understand and guide production of uniform bulk samples of this composite, the liquidus projection of quaternary Pb-Ag-Sb-Te system at 36.0 at.% Te isoplethal section is constructed experimentally, using quenched samples. A three-phase univariant reaction of the quaternary Pb-Ag-Sb-Te system, L ! AgSbTe 2 +Ag 2 Te + d-Sb 2 Te, is investigated, between a ternary-eutectic melt (Ag-40.0 at.% Sb-36.0 at.% Te) and a quaternary melt (Pb-22.0 at.% Ag-40.0 at.% Sb-36.0 at.% Te), at 496.1°C and 503.9°C, respectively. High-resolution transmission electron microscopy confirms that these three phases are simultaneously present at the nanometer scale. Furthermore, unidirectional solidification experiments of the ternary eutectic alloy using the Bridgman method are carried out to examine the alloy's solidification behavior.
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