Alloys and Compounds for Thermoelectric and Solar Cell Applications VIII: Session III
Sponsored by: TMS Functional Materials Division, TMS: Alloy Phases Committee
Program Organizers: Sinn-wen Chen, National Tsing Hua University; Franck Gascoin, Ensicaen University of Caen; Philippe Jund, Montpellier University; Yoshisato Kimura, Tokyo Institute of Technology; Lan Li, Boise State University; Takao Mori, National Institute For Materials Science; Hsin-jay Wu, National Chiao-tung University; Tiejun Zhu, Zhejiang University
Wednesday 8:30 AM
February 26, 2020
Room: Miramar
Location: Marriott Marquis Hotel
Session Chair: Takao Mori, National Institute for Materials Science; Philippe Jund, Université de Montpellier
8:30 AM Invited
Ab initio Calculations of Thermoelectric Materials: Laurent Chaput1; 1University De Lorraine
Since the last few years it has been possible to obtain the lattice thermal conductivity of semiconductors and insulators from first principle calculations, with good accuracy.We have recently developed a computational method that allow computing the electron-phonon interactions efficiently. This allow obtaining the electronic contributions to the thermoelectric figure of merit from first principles as well. Several example along those lines will be investigated, and the current status of ab initio calculations for thermoelectricity will be discussed.
8:50 AM Invited
Ab-initio Study of TiMSn (M= Ni, Pt, Pd) Alloys using the CRYSTAL Ab-initio Package.: Lorenzo Maschio1; Atreyi Dasmahapatra1; Loredana Daga1; Antti Karttunen2; Silvia Casassa1; 1University of Torino; 2Aalto University
Half-Heusler (HH) alloys are among the most well known thermoelectric (TE) materials. In this contribution, we present a detailed study of the TE properties of TiMSn (M = Ni, Pd, Pt) HH alloys using local Gaussian orbitals and hybrid density functional theory methods as implemented in the CRYSTAL code[1,2]. In addition to pure bulk systems, we aim at explaining existing discrepancies between calculations and experiment by modeling defects in the pure system at realistic dilution. [1] R. Dovesi, A. Erba, R. Orlando, C. M. Zicovich-Wilson, B. Civalleri, L. Maschio, M. Rerat, S. Casassa, J. Baima, S. Salustro, B. Kirtman. WIREs Comput Mol Sci. 8, e1360 (2018). [2] G. Sansone, A. Ferretti, L. Maschio, J. Chem. Phys. 147, 114101 (2017)
9:10 AM Invited
Defect Formation Energies and Effective Masses in the Mg2(Si,Sn) Solid Solutions via DFT Calculations: Philippe Jund1; Alexandre Berche1; Johannes de Boor2; 1Montpellier University; 2DLR Köln
Thermoelectric generators can convert heat directly into usable electrical energy. One material class of particular interest are the solid solutions based on Mg2Si and Mg2Sn. While these show promising thermoelectric properties, the role and influence of intrinsic defects (vacancies, interstitials, antisites) and extrinsic defects (e.g. due to dopants) on the thermoelectric properties are still not fully understood and might be a lever to increase the material performance further.In this study we present first principles calculations of the formation energy of intrinsic defects in the compounds Mg2Si(1-x)Snx with x=0 to 1 as well as the evolution of the effective masses (an important parameter for the efficiency of the TE conversion) with x. A good agreement with the experimental measurements of the masses is found on the tin rich side whereas this is not the case on the silicon rich side.
9:30 AM
Using Energy Filtering to Change the Thermoelectric Design Paradigm: Seyed Aria Hosseini1; Jackson R. Harter,2; Devin Coleman1; Lorenzo Mangolini1; Alex Greaney1; 1University of California, Riverside; 2Oregon State University
Researchers have recently developed processes for synthesizing monolithic Si with improved ZT. These materials obtain higher ZT through a finely controlled array of secondary phase inclusions. In this work we elucidate the role these particles play in (1) scattering of phonons to reduce thermal conductivity, and (2) selective scattering of electrons to increase seebeck coefficient. For (1) Boltzmann transport simulations are used to predict the collective effect of the scattering mechanisms on thermal conductivity. For (2) Fermi’s golden rule is used to compute electron scattering interactions with nanoparticles. We further present a semiclassical transport model in the presence of selective electron scattering. This model predicts that the highest ZTs can be achieved in the tails of the Fermi-dirac distribution of highly doped thermoelectrics. This presents a new strategy for optimization of thermoelectrics that breaks materials engineers free from the traditional paradigm of engineering the fermi energy at the band edge.
9:50 AM
Accelerated Discovery of Efficient Solar-cell Materials using Quantum and Machine-learning Methods: Kamal Choudhary1; Francesca Tavazza2; 1University of Maryland (National Institute of Standards and Technology); 2Umcp/National Institute of Standards and Technology
Solar-energy plays an important role in solving serious environmental problems and meeting high-energy demand. However, the lack of suitable materials hinders further progress of this technology. Here, we present the largest inorganic solar-cell material search to date using density functional theory (DFT) and machine-learning approaches. We calculated the spectroscopy limited maximum efficiency (SLME) using Tran-Blaha modified Becke-Johnson potential for 5097 non-metallic materials and identified 1997 candidates with an SLME higher than 10%, including 934 candidates with suitable convex-hull stability and effective carrier mass. Screening for 2D-layered cases, we found 58 potential materials and performed G0W0 calculations on a subset to estimate the prediction-uncertainty. As the above DFT methods are still computationally expensive, we developed a high accuracy machine learning model to pre-screen efficient materials and applied it to over a million materials. Our results provide a general framework and universal strategy for the design of high-efficiency solar cell materials.
10:10 AM Break
10:30 AM Invited
Utilizing Magnetism and Dilute Magnetic Semiconductors to Enhance Thermoelectric Performance: Takao Mori1; 1National Institute for Materials Science
We have previously proposed to utilize magnetic interactions between carriers and magnetic moments to enhance the thermoelectric (TE) power factor [1,2]. Magnetic interactions can also be created in non-magnetic materials by magnetic-ion doping, e.g. CuGaTe2, BiCuSeO, Bi2Te3, SnTe, etc. [2]. The interaction affects the carriers by making them heavier, like a "drag" effect, enhancing the Seebeck effect. However, unlike magnon drag, TE enhancement via magnetic interaction is not solely dependent on ordering, and is effective at higher temperatures also. We have also demonstrated significant enhancement of the Seebeck coefficient via spin fluctuation. This is indicated to more than double the power factor in a Heusler compound [3]. [1] Appl. Phys. Express, 6, 043001 (2013) , Angew. Chem. 54, 12909 (2015), Chem. Mater., 29, 2988 (2017), Small, 13, 1702013 (2017). [2] J. Mater. Chem. A, 5, 7545 (2017), Materials Today Phys. , 9, 100090 (2019).[3] Science Advances, 5, eaat5935 (2019).
10:50 AM Invited
Multi-band Electronic and Thermal Transport in Fe2VAl Based Full Heusler Thin Films: Ernst Bauer1; Bernhard Hinterleitner1; Alexander Riss1; Takao Mori2; Xingqiu Chen3; 1Vienna University of Technology; 2National Institute for Materials Science, Tsukuba; 3Shenyang National Laboratory for Materials Science, Shenyang
We have synthesized a series of Fe2(V,W)Al based samples by magnetron sputtering. Besides an astonishingly large value of the power factor, the thermal conductivity appears to be reduced. Consequently, the thermoelectric figure of merit is very large. In the present work, we are investigating the origin of the large power factor observed and found that a favourable electronic band structure, with multi-valley character and huge charge carrier velocities might be a possible origin for this observation. Employing Hall effect measurements at high temperatures and high magnetic fields reveal the presence of different sets of charge carriers. Using a modified two-band model, a qualitative and quantitative microscopic picture emerges with substantially enhanced charge carrier mobility values.This work is supported by the CDL for Thermoelectricity, and the JST, CREST (JPMJCR15Q6, JPMJCR19Q4). Work in China, was supported by Projects No. 51725103, Nos. 51671193 and 51474202, No. TZ2016004.
11:10 AM
Portable Nanostructured Magneto-Thermoelectric Bi-Sb Alloys at Cryogenic Temperatures: Joseph Poon1; 1University of Virginia
Thermoelectrics play a vital role in heat-to-electrical energy conversion and refrigeration. Bismuth antimony is a promising material for thermoelectric cooling. A high figure of merit ZT~ 0.6 at 100K was measured in nanocrystalline n-type Bi-Sb, 50% higher than the polycrystalline ZT 0.4. Magneto-thermoelectric effects further improved the TE properties, increasing ZT to 0.7 in a portable compact BiSb/NdFeB system. The improved thermoelectric properties can be attributed to the nanostructure achieved from rapid solidification, which not only significantly reduced the thermal conductivity but also avoided phase segregation. The thermoelectric properties were analyzed within a two-band model to provide a deeper understanding of the transport mechanisms. The study revealed a heretofore unknown narrowing of the band gap at increasing temperature. The easily accessible low magnetic field for high ZT enables the utilization of BiSb in thermoelectric cooling.In collaboration with Sheng Gao, Dr. John Gaskins, Xixiao Hu, and Prof. Patrick Hopkins.
11:30 AM
Phase Diagrams of Ag-Cu-Te Ternary System and Ag2Te/Cu Interfacial Reaction: Yohanes Hutabalian1; Sinn-wen Chen1; 1National Tsing Hua University
The Ag-Cu-Te ternary system is of thermoelectric application interests. The phase diagrams of Ag-Cu-Te ternary system and the Ag2Te/Cu interfacial reactions at 400 ℃ and 600℃ are investigated in this study. Ternary alloys of Ag-Cu-Te were prepared and equilibrated at 400℃ and 600℃, and their equilibrium phases are determined. The phase diagrams of the binary systems, Ag-Te and Cu-Te, were reassessed. In the Ag-Te binary system, there are two compounds, Ag2Te, Ag1.9Te and Ag5Te3. There are three binary compounds, Cu2Te, Cu3Te2 and CuTe, in the binary Cu-Te system. There is one ternary compound, AgCuTe. Isothermal sections at these two temperatures were constructed based on the ternary experimental results, the phase diagrams of the three constituent binary systems, and experimental results of the ternary system in the literature. Two reaction phases, Ag and AgCuTe, are found in the reaction couples. The reaction path is illustrated using the determined isothermal section.
11:50 AM
Optimization of Thermoelectric Performance of Nitrogen- and Boron-doped Carbon Nanotubes: Manaho Matsubara1; Kenji Sasaoka1; Takahiro Yamamoto1; 1Tokyo University of Science
Significant enhancement of thermoelectric performance is expected to be achieved by utilizing one-dimensional (1D) materials. Single-walled carbon nanotubes (SWNTs) are potential candidates for 1D nanostructures with high thermoelectric performance as well as flexibility and lightweight. To achieve CNT-based thermoelectric devices, both n-type and p-type semiconducting CNTs are required. We focus on nitrogen-doped (N-substituted) and boron-doped (B-substituted) SWNTs as a typical n-type and p-type semiconducting SWNTs, and we have investigated their thermoelectric properties based on Kubo-Lüttinger theory for thermoelectric effects. In this invited talk, we present that the N-substituted SWNTs exhibit high thermoelectric power factor (PF) when the chemical potential locates neat the conduction band edge. This originates from sharp density of states due to van Hove singularity of 1D materials and high mobility of conduction electron with small effective mass. In addition, we give the optimal N and B concentrations to maximize PF for semiconducting SWNTs with various diameters.
12:10 PM
Thermoelectric Films Deposited by Pulsed Magnetron Sputtering: Elzbieta Godlewska1; Krzysztof Mars1; Kinga Majewska-Zawadzka1; Wojciech Sznajder1; 1AGH UST
Thin films have potential to surpass bulk materials with a similar composition in terms of thermoelectric properties because of much lower thermal conductivity. This idea was followed in the investigations on magnetron sputtered Cu-Se films. Targets with a desired Cu:Se atomic ratio close to 2:1 were produced by melting and solidification in the evacuated quartz ampoules, grinding into powders, hot pressing and machining. Thin films were deposited on glass substrates or on silicon wafers. Doping trials of the baseline composition were executed by means of an additional target installed in the experimental set-up. Morphology, chemical composition and phase composition of the films were routinely characterized by SEM/TEM, EDS and XRD. Thermoelectric properties were evaluated by means of LINSEIS Thin Film Analyzer which enables simultaneous determination of all crucial physical parameters on one sample during one measurement run. Financial support from the National Science Centre Poland (UMO-2016/23/B/ST8/01248) is gratefully acknowledged.