Work

First-Principles Based Phonon Calculation and Raman Spectroscopy Measurement of RuGa2 and RuAl2 with High Thermoelectric Power Factor

Year: 2015

Type: article

Abstract: TiSi2-type intermetallic compounds RuGa2 and RuAl2 have narrow band gaps of ~0.3 eV and a relatively large power factor at 600–900 K. However, the maximum dimensionless figure of merit, ZT, are 0.5 and 0.2 for RuGa2 and RuAl2, respectively, due to a high lattice thermal conductivity. We investigated the phonon properties of these compounds by using a first-principles calculation and Raman spectroscopy to develop a further reduction scheme of the lattice thermal conductivity. Phonon dispersion relations and density of states were obtained from a real-space force constants method based on supercells with finite displacements. The calculated zone-center wavenumbers were comparable to the experimental Raman wavenumbers. Besides, the phonon group velocities of acoustic branches were in accord with the experimental transverse and longitudinal speed of sound. The differences of phonon dispersion between RuGa2 and RuAl2 are explained by the fact that Ga is heavier and weaker bonding element than Al. According to the calculated partial phonon density of states, acoustic phonon modes of RuGa2 and RuAl2 are attributed to Ga site and Ru site, respectively. Heavier atom substitution for these sites can effectively reduce averaged phonon group velocity and lattice thermal conductivity.

Source: Journal of the Japan Institute of Metals and Materials

DOI: 10.2320/jinstmet.ja201510

Authors: N. Sato, Y. Takagiwa, A. Kuwabara, N. Uchida, K. Kimura

Institutions: The University of Tokyo, Japan Fine Ceramics Center, National Institute of Advanced Industrial Science and Technology

Language: English

Topic: Advanced Thermoelectric Materials and Devices

Subfield: Materials Chemistry

Field: Materials Science

Domain: Physical Sciences

Open Access status: diamond

Funder: Japan Society for the Promotion of Science

Award: パノスコピック構造制御による高性能熱電材料の創製