Alloys and Compounds for Thermoelectric and Solar Cell Applications IX: Poster Session
Sponsored by: TMS Functional Materials Division, TMS Structural 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; Lan Li, Boise State University; Takao Mori, National Institute For Materials Science; Tiejun Zhu, Zhejiang University; Alexandra Zevalkink, Michigan State University; Wan-Ting Chiu, Tokyo Institute of Technology
Monday 5:30 PM
March 15, 2021
Room: RM 21
Location: TMS2021 Virtual
A Synergistic Approach to Boost the Thermoelectric Performance and Reduce the Thermal Conductivity in n-type PbTe : Carrier Optimization and Phase Diagram Engineering: Ping-Yuan Deng1; Kuang-Kuo Wang2; Jia-Yu Du3; Hsin-Jay Wu1; 1National Chiao Tung University; 2National Sun Yat-sen University; 3National Tsing Hua University
PbTe-based alloys with dopants have been the important mid-temperature thermoelectric (TE) materials since the 1960s. The breakthroughs for n-type PbTe are less impressive, which limits the overall conversion efficiency of a PbTe-based TE device. To overcome this obstacle, the electron-donor Gallium is incorporated with the PbTe, aiming to introduce the additional impurity traps within the bandgap. Additionally, the κL unveils a significant declining trend, accompanying with the defect evolution that transforming from a dislocation loop to nano-precipitation with increasing Ga content. The mechanism behind the κL reduction can be clarified by an equilibrium phase diagram, which opens up a new avenue for locating the high-zT TE materials. The synergy approach of carrier optimization and hierarchical architecturing rejuvenate the well-established TE materials and boost their performance to a higher record.
Co-P Diffusion Barrier for Lead Telluride-based Thermoelectric Joints: Kai-Wen Cheng1; Hsien-Chien Hsieh1; Albert T. Wu1; 1National Central University
PbTe-based alloys show excellent thermoelectric performance at medium temperature range. The formation of intermetallic compounds between thermoelectric materials and electrodes deteriorates mechanical joint strength and thermoelectric performance. In this study, directly bonded Ni and Cu electrode induced formation of IMCs and disintegration of the joints in both p- and n-PbTe modules. Severe interfacial problems are overcome by utilizing an electroless cobalt-phosphorus (Co-P) diffusion barrier. The mechanical strength is improved owing to the insertion of Co-P diffusion layer, and the additional layers yield acceptable contact resistance. In addition, the added layers enhance thermoelectric performance and thermal stability in p- and n-PbTe materials. The fabricated p-type and n-type PbTe-based thermoelectric joints meet the required criteria for improving efficiency of PbTe modules.
Ni/Pb-Te and Ni/Se-Sn Interfacial Reactions and Their Related Phase Diagrams: Yohanes Hutabalian1; Zhi-kai Hu1; Xu-hui Chen1; Sinn-wen Chen1; 1National Tsing Hua University
PbTe-based and SnSe-based alloys are promising thermoelectric materials. Ni is frequently used as diffusion barrier. Interfacial reactions in Ni/PbTe, Ni/SnSe and Ni/SnSe2 couples are examined. Ni-Pb-Te and Ni-Se-Sn phase diagrams are assessed and used for the illustration of the interfacial reactions. The results indicate the reaction path is Ni/Ni3Te2/Ni5Pb2Te3/Liquid(Pb)/PbTe for the Ni/PbTe couples reacted at 650℃. Complicated reaction phenomena are observed. Three reaction zones are formed in the Ni/SnSe2 couples reacted at 500oC for 30 min. The three zones are clearly distinguishable, and all of them are not of single phase. Similar results are observed in the Ni/SnSe2 couples reacted at 300oC for 5 days. Thee reaction zones which are composed of multi-phases are formed. Since the average compositions of each of the three zones are along the mass balance line between Ni and SnSe2, it is very likely Ni penetrates into the SnSe2 substrate.
Ultra-low Thermal Conductivity for High-performance GeTe-based Thermoelectric Materials: Yi-Fen Tsai1; Hsin-Jay Wu1; 1National Chiao Tung University
In recent years, Germanium-tellurides (GeTe) alloys were viewed as promising thermoelectric materials. Due to the presence of Ge vacancies, GeTe featured with high carrier concentration, high electrical conductivity and high thermal conductivity. With the incorporation of minor amount of group-IB group-VA and elements, both the carrier concentration and thermal conductivity can be effectively reduced, yielding a high thermoelectric figure-of-merit zT. Specially, the optimization counts on an equilibrium phase diagram, which offers a new avenue toward high-performance TE materials.
Using Neutrons to Probe the Influence of Processing on Temperature-dependent Strain in PbTe: James Male1; Riley Hanus1; G Snyder1; Raphael Hermann2; 1Northwestern University; 2Oak Ridge National Laboratory
Several recent breakthroughs in high zT PbTe-based materials reduce thermal conductivity by introducing dislocations. The defective core of a dislocation scatters phonons, while surrounding strain fields soften the lattice and reduce phonon velocity. The latter effect, lattice softening, accounts for much of the thermal conductivity reduction previously attributed to nanostructure phonon scattering in high zT PbTe. Through neutron diffraction experiments, we find that extensive ball milling doubles the amount of strain in undoped PbTe relative to nominally unstrained samples, but strain anneals out at high temperatures. Introducing extrinsic Eu and/or Na dopants increases the strain by another factor of two and assists in keeping strain in the sample at higher temperatures, which is desirable for high temperature performance. These results give direct insight into the ability to introduce and maintain strain in PbTe while providing direct explanations for impressively low thermal conductivities in recent groundbreaking PbTe-based materials.