Alloys and Compounds for Thermoelectric and Solar Cell Applications XI: Session III
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; Takao Mori, National Institute For Materials Science; Wan-Ting Chiu, Tokyo Institute of Technology; Chenguang Fu, Zhejiang University
Tuesday 8:00 AM
March 21, 2023
Room: Sapphire A
Location: Hilton
Session Chair: Yi-Fen Tsai, National Yang Ming Chiao Tung University; I-Lun Jen, National Yang Ming Chiao Tung University
8:00 AM Invited
Bi2Te3 Based Compounds Made via Mechanical Alloying: Defect Chemistry and Phase Diagram: Franck Gascoin1; Amélie Galodé1; 1Cnrs Crismat Unicaen
Despite the efforts devoted to the development of new thermoelectric materials, it is a fair and unfortunately not so surprising that bismuth telluride based materials are still the only one used in commercial thermoelectric devices. The performances of these materials are well known and their synthesis rather straight forward, however the relationships between their properties and the way they are produced are still puzzling as it is mainly the type and number of defects that govern their electronic transport properties. In this presentation, we will show our preliminary results on our attempts to tame the defect chemistry in these materials, both in terms of pure thermoelectric performance “ZTmax” and temperature at which this occurs (Tmax).
8:20 AM Invited
Enhancement of Phonon Scattering in Thermoelectric Half-Heusler Compounds by Non-equilibrium Synthesis: Ran He1; 1IFW-Dresden
Preventing phonon transport remains one of the most challenging tasks to improve the thermoelectric performance of certain materials such as half-Heusler compounds. On the other hand, established strategies such as alloying or grain boundary refinement have almost exhausted their potential to further reduce the lattice thermal conductivity (κL). It is still unclear how to further improve the phononic scattering of these materials. In this talk, I will show that thermal conductivity can be drastically reduced by non-equilibrium synthesis. Two unconventional strategies for thermoelectric studies will be presented, including cryogenic milling and high-pressure sintering. A maximum κL reduction of 83% was achieved at room temperature with a relative density greater than 95%. Our work uncovers the phonon transport properties of half-Heusler compounds under unconventional microstructures, showing the potential of high-pressure compaction and cryogenic milling to advance the performance of thermoelectric materials.
8:40 AM
Influence of Connectivities and Length Scales of Eutectic Alloys on Thermoelectric Properties: Panithi Sireesha1; Shriparna Mukherjee1; Shanmukha Kiran Aramanda1; Kamanio Chattopadhyay1; 1Indian Institute of Science
Thermoelectric materials are usually designed by varying compositions. However, microstructural control provides an opportunity to fine-tune the properties. Eutectic solidification generates self-organized structures with different microstructural scales and can be used for producing complex thermoelectrics. In a comparative study, we have investigated two extreme cases of eutectic solidification: directional solidification and rapid quenching. For the directional solidification, we utilized Cu2Te-Sb2Te3 as a model system, while for the quenching technique, we used SnTe-Te. In the Cu2Te-Sb2Te3 system, lower growth condition led to a uniform microstructure (segregation-free), which exhibited a maximum PF (∼1.4 mW/m-K^2) and a higher zT of 0.29, while the higher growth conditions showed deteriorated properties due to cellular segregation. In the SnTe-Te system, higher growth conditions imparted through a higher cooling rate led to the formation of nano-lamellae features that improved PF (∼1.1 mW/m-K^2) and a higher zT of 0.45.
9:00 AM Invited
Young Leaders International Scholar – JIM: Discovery of Triple Half-Heusler with Low Thermal Conductivity: Kazuki Imasato1; Philipp Sauerschinig1; Shashwat Anand2; Takao Ishida1; Atsushi Yamamoto1; Michihiro Ohta1; 1National Institute of Advanced Industrial Science and Technology; 2Lawrence Berkeley National Laboratory
Half-Heusler (HH, general formula: XYZ) materials have been extensively researched for their potential in thermoelectric materials and other applications. The concept of double half-Heusler (DHH) was recently proposed as a potential strategy to reduce lattice thermal conductivity for better thermoelectric performance. In this talk, we will expand this idea further to triple half-Heusler (THH). THH phase was successfully synthesized by following an unconventional valence balance strategy. Even though both ternary components of THH phase are unstable with the metallic transport properties, experimental results indicated a homogeneous and pure characteristic of synthesized samples with a large Seebeck coefficient. In addition, the lattice thermal conductivity is lower than half-Heusler standards around room temperature. Since a high thermal conductivity has been always a problem for HH-based thermoelectric materials, the synthesis of THH with very low lattice thermal conductivity can be a new direction for the high-performance of HH thermoelectrics.
9:30 AM Break
9:50 AM Invited
Doping as a Tuning Mechanism for Magneto-thermoelectric Effects to Improve zT in Weyl Semimetals: Sarah Watzman1; 1University of Cincinnati
Weyl semimetals combine topological and semimetallic effects, making them interesting candidates for thermoelectric transport. Experimental results in polycrystalline NbP demonstrate the simultaneous existence of a large Nernst and magneto-Seebeck effect, which is typically not observed in a single material at the same temperature. We compare transport results among differing samples of NbP, observing a shift in the temperature at which the maximum Nernst and magneto-Seebeck thermopowers occur. Theoretical modeling shows doping strongly alters both the Seebeck and Nernst magneto-thermopowers by shifting the temperature-dependent chemical potential. Thus, we offer doping as a tuning mechanism for shifting magneto-thermoelectric effects to temperatures appropriate for device applications, improving zT at desirable operating temperatures. Furthermore, the simultaneous presence of both a large Nernst and magneto-Seebeck thermopower is uncommon and offers unique device advantages if the thermopowers are used additively. Thus, we propose a thermoelectric device which would collectively harness the large Nernst and magneto-Seebeck thermopowers.
10:10 AM Invited
Carrier Concentration Adjustment and Texturation Processing on Thermoelectric Silicide: David Berthebaud1; 1French National Center for Scientific Research
We will present our recent results on silicide materials (CrSi2 and MnSiγ) which were selected for their low cost and/or advantageous properties. For example, the Nowotny-chimney ladder compounds MnSiγ (γ ~ 1.73) is particularly interesting as it exhibits sufficiently high ZT values (≥ 0.5 at 500 °C) in a wide temperature range, which is an advantage for stable electricity production. These advantages render them ideal candidates for the development of industrial prototypes. CrSi2 is also an interesting p-type alternative materials with similar structural features to above mentioned one, and we will present here recent results on the improvement of its thermoelectric properties through a slip-casting process under a strong magnetic field.
10:30 AM
Order-disorder Transitions in Zr-doped NbCoSn Heusler Alloys Enable Tunable n-p Transitions: Nathan Johnson1; 1Stanford University
Thermoelectric NbCoSn heusler alloys have demonstrated a transition in carrier type as the unit cell is doped with increasing Co. The transition occurs near the half heusler composition. It has also been observed that the maximum Seebeck coefficient for either carrier type increases with shorter annealing times. We show that the n-p transition effect and the higher Seebeck coefficients are linked to an order-disorder transition in the NbCoSn unit cell near the half heusler composition. We use X-ray diffraction to solve the ordering of the unit cell at different compositions and annealing times. Diffraction experiments are coupled with thermoelectric property measurements. We then use a density functional theory approach to show how the change in unit cell ordering modifies the electronic structure of the crystal. As more Co is doped into the unit cell, the crystal experiences a symmetry change that likewise modifies the band structure and the carrier composition.
10:50 AM
In-situ Creep Deformation Electrical Conductivity Measurement of I-doped PbTe: Muath Almalki1; Yukun Liu1; James Male1; Vinayak Dravid1; David Dunand1; G. Jeffrey Snyder1; 1Northwestern University
Although the mechanical behavior of thermoelectric materials has been gaining interest in the community, little has been done to understand its real impact on the transport properties. Creep deformation could be one of the design limitations, not just because of the introduced dimensional instability, but also due to the impact it leaves on the electronic transport. In this talk, we report the in-situ high temperature creep-electrical conductivity measurement for I-doped PbTe. There, the drop in electrical conductivity was shown to scale linearly with the strain, Minimal direct influence of point defects is expected, and such conductivity drop is attributed mainly to the increased dislocation density. TEM examination of the deformed samples revealed the formation of sub-grain boundaries that are considered stable against climb annihilation. This, in fact, opens a door to introduce stable dislocations structures with minimal impact on the electrical conductivity, but significant enough to reduce the thermal counterpart.
11:10 AM
Enhanced Mechanical Properties of Ti-rich Medium Entropy Alloys via Phase Diagram Engineering: Wen-Chi Yang1; Ping-Yuan Deng1; Hsin-Jay Wu1; 1National Yang Ming Chiao Tung University
Medium entropy alloys (MEAs) have gained attention for their excellent mechanical properties, such as high strength and relatively high ductility that could even outperform the well-established and commercially-useTi-6Al-4V. In particular, the MEAs comprising elementsof Al and Ti attract enormous attention due to their lightweight feature comparing to well-developed CoCrNi MEAs. This study constructs the phase diagrams of Ti-Al-Cr-V by experiments. Alongside the phase diagram determination, the microstructural evaluation and structural transformation for MEAs were captured. The ordered B2 phase can be clearly distinguished from the disordered BCC phase via synchrotron x-ray measurements. By associating the metallographic information with physical properties, promising MEAs with enhanced mechanical properties and desired transport properties can be located via the phase diagram engineering.