Alloys and Compounds for Thermoelectric and Solar Cell Applications X: On-Demand Poster Session
Sponsored by: TMS Structural Materials Division, TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Hsin-Jay Wu, National Chiao Tung University; Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, CNRS Crismat Unicaen; Philippe Jund, Montpellier University; Yoshisato Kimura, Tokyo Institute of Technology; Takao Mori, National Institute For Materials Science; Alexandra Zevalkink, Michigan State University; Wan-Ting Chiu, Tokyo Institute of Technology; Pai-chun Wei, National Taiwan University

Monday 8:00 AM
March 14, 2022
Room: Electronic Materials
Location: On-Demand Poster Hall


Enhancing Thermoelectric Performance via Delaying Transition Temperature in GeTe Alloys: Yi-Fen Tsai1; Hsin-Jay Wu1; 1National Chiao Tung University
    Germanium-tellurides (GeTe) are promising thermoelectric materials owing to their outstanding thermoelectric (TE) performance in the mid-temperature range. Meanwhile, the temperature-dependent structural transition in GeTe-based alloy could directly affect the gradient of the transport properties. Microstructural engineering, as well as stoichiometric controlling, are powerful approaches to suppress the phase transition. Examples can be given in Cu2S-GeTe alloy, which appears 149% reduction in thermal conductivity. In addition, the transition temperature shifts toward higher temperature in order to enlarge the temperature range of -GeTe. In short, stoichiometric controlled Cu2S-GeTe shows superior TE performance through microstructural engineering.

High Thermoelectric Performance in n-type PbTe Enabled by Carrier Optimization and Nano-precipitates: Ping-Yuan Deng1; Kung-Kuo Wang2; Hsin-Jay Wu1; 1National Yang Ming Chiao Tung University; 2National Sun Yat-sen University
    Lead telluride has been the most attactive mid-temperature thermoelectric (TE) materials since the 1960s. However, the TE performance of the n-type PbTe is still low, which limits the overall conversion efficiency of a PbTe-based TE device. To make a breakthrough, the interstitial-Cu is incroporated into the PbTe to improve the power factor as result of elevating carrier mobility. The electromigration effect deteriorates the TE performance due to the nature of mobie Cu under the electrical current, showing poor thermal stability after mutiple cycling. Benefited from lightly Cu doping and VIA-element alloying, the Cu0.012M0.006(PbTe)0.988 (M = VIA elements) performs a peak zT ~ 1.5 at 598 K with high thermal stability after cycling. The co-existence of interstitial-Cu and VIA nano-precipitate maintain the large carrier mobility with a reduced kL, eliciting a high TE performance n-type PbTe that present high thermal stability below 600 K.

Interfacial Reactions in Ni/Se,Te) and Ni/Pb1-xSnxSe Couples: Yohanes Hutabalian1; Hsu-Hui Chen1; Zhi-Kai Hu1; Sinn-wen Chen1; 1National Tsing Hua University
    The interfacial reactions in the Ni/(Se-90.0at.%Te) and Ni/Pb1-xSnxSe (x=0.1, 0.2, 0.3) couples reacted at 500oC are examined. At 500oC, Se-90.0at.%Se is molten and Pb1-xSnxSe is solid. Two reaction phase layers, Ni3Te2 and NiTe2, are found in the solid Ni/liquid Se-90at.%Te couple, and there are concentration gradients in the liquid phase after reaction. The reaction path is Ni/Ni3Te2/NiTe2/Liquid. The Sn-doped-PbSe phase, Pb1-xSnxSe, retains the crystal structure of PbSe. A ternary compound, Ni3Pb2Se2, was found in the Ni/PbSe couples. The interfacial reaction results in the Ni/Pb1-xSnxSe (x=0.1, 0.2, 0.3) couples are similar to those in the Ni/PbSe couples and the Ni3Pb2Se2 phase is found. But, depending upon Sn contents, much more complicated results are formed, and a second phase with composition about Ni5.62SnSe2 is found. It was found that Ni is the fastest diffusion species. The related phase diagrams are assessed and used for the illustration of the above-mentioned interfacial reactions.

Lightly Impurity Doping and Entropy Engineering Synergy Realizing High-performance n-type Bi2Te3 Thermoelectrics: Wan-Ting Yen1; Hsin-jay Wu1; 1National Yang Ming Chiao Tung University
    Bi2Te3 has been the most high-performance thermoelectric (TE) cooling material since the 1960s. To date, the TE property of n-type Bi2Te3-based is still lower than p-type Bi2Te3-based material. Therefore, n-type materials attract a lot of attention and effort. Herein, according to the light impurity doping and entropy engineering, the TE performance of n-type Bi2Te3 was improved. Lightly doping of Ag, Cu, S, Se elements in Bi2Te3 alloy conduces to improve the carrier mobility without affected the band structure of Bi2Te3. In particular, an entropy engineering approach by using the doping of four elements (Ag, Cu, S, Se) is being adopted to reduce the thermal conductivity of the n-type Bi2Te3-based. Therefore, the lightly doped (Ag, Cu, S, Se)-Bi2Te3 alloy achieves high power factor and low thermal conductivity, which improves the TE performance of n-type Bi2Te3.

N-type Silver Chalcogenide with Excess Ag Leading to Improved Thermoelectric Properties : You-Cheng Du1; Wan-Ting Yen1; Hsin-Jay Wu1; 1National Yang Ming Chiao Tung University
    Nowadays bismuth tellurides are still the best thermoelectric materials at low temperature range because of their well performance in thermoelectric cooler. However, the silver chalcogenides have the advantages of earth-abundance and low-toxicity, which enhances their competitiveness in low temperature application. Single crystalline Ag2Se and Ag2Te were fabricated from the Bridgman method while the excess Ag was deposited by sputtering. The lattice thermal conductivity was further reduced by the highly mobile silver ions that introduce various scale of defects and enhance the phonon scattering. It was discovered that the slight composition difference in silver chalcogenides would lead to great variety of thermoelectric performance. Moreover, the excess Ag in our Ag2+x crystals increase electrical conductivity and bring enhanced power factor at the near room-temperature region, making the n-type silver chalcogenides as ideal candidates for n-type TE cooler.

Realizing High Thermoelectric Figure of Merit of Co-doped GeTe Alloy via Phase Diagram Engineering: Szu-Chien Wu1; Yi-Fen Tsai1; Hsin-Jay Wu1; 1National Yang Ming Chiao Tung University
    GeTe-based alloys have shown promising thermoelectric performance in recent years. Phase diagram engineering has been proposed as an effective strategy to optimize the thermoelectric properties through manipulating microstructure. Based on the Sn-Ge-Te phase diagram, a structural transition zone exists between the rhombohedral- and cubic-(SnTe, GeTe) solid solution. In order to maintain rhombohedral structure, lightly doping is adopted. Lightly Sn-doped GeTe solid solution shows the decent electrical conductivity σ and power factor PF = S2σ. However, Sn substitution scarcely decreases the carrier concentration, and thermal conductivity remains a high value at high temperature. Therefore, slightly Sb and Bi co-doping are introduced to optimize the carrier concentration and thermal conductivity. The large mass fluctuation caused by co-doping significantly reduces the lattice thermal conductivity. The lightly co-doped rhombohedral-GeTe alloys show promising thermoelectric performance.

The Wurtzite CuFeS2 Thin Film and Its Phase Transformation to Chalcopyrite for Thermoelectric Generator: Hong Pang1; Cédric Bourgès1; Naohito Tsujii1; Takahiro Baba1; Naoki Sato1; Tetsuya Baba1; Takao Mori1; 1National Institute for Materials Science
    Utilizing magnetic semiconductors to obtain enhanced thermoelectric (TE) performance has been demonstrated in the cases where the electrical carriers have strong interaction with the magnetic moments. Thin film offers tremendous scope for TE materials by eliminating the scattering of carriers and minimization of thermal conductivity. Herein this work, the prototypical magnetic semiconductor chalcopyrite, CuFeS2-type thin films was targeted. The non-equilibrium condition in the radio frequency magnetron sputtering provides the possibility to form the elusive metastable compound from ambient environment. A novel metastable wurtzite CuFeS2 thin film was fabricated via co-sputtering deposition and disclosed with a promising thermoelectric harvesting capability. Further investigation reveals that Zn doping and high temperature stage can activate the phase transformation from metastable wurtzite structure to the thermodynamically stable chalcopyrite phase. A power factor of ~0.17 mW·m-1·K-2 at room temperature has been obtained so far, and other TE properties are investigated.