Synchrotron-radiation X-raypowder diffraction study of alpha- and beta-Zn₄Sb₃compounds

T. Souma¹,G. Nakamoto¹, M. Kurisu¹, K. Kato², M. Takata^2,3

¹Japan Advanced Institute ofScience and Technology, Tatsunokuchi, Ishikawa 923-1292, Japan

²Japan Synchrotron RadiationResearch Institute/SPring-8, Hyogo 679-5198, Japan

³Department of Applied Physics,Nagoya University, Nagoya 464-8603, Japan

Beta-Zn₄Sb₃compound has been recently identified as a new thermoelectric material withhigh figure of merit of ZT=1.4 at 670 K. However, there have been few thermoelectricdata on the low-temperature alpha-phase, which is stable below 263 K.Furthermore, the crystal structure of the alpha-Zn₄Sb₃and the details of the structural phase transition from the alpha- tobeta-phase have not been reported yet. In this study, we have investigated thecrystal structures of the alpha- and beta-Zn₄Sb₃ by anX-ray powder diffraction in the temperature range of 180 to 295 K. Thesynchrotron-radiation X-ray powder experiments have been performed at theSPring-8 BL02B2 station. The diffraction patterns of Zn₄Sb₃have been refined by the Rietveld profile fitting program RIETAN-2000. All thediffraction peaks of the alpha-Zn₄Sb₃ at 180 K areindexed by assuming a rhombohedral structure with the space group of R-3c as in the beta-Zn₄Sb₃.A drastic increase in the c/ais observed at the structural phase transition temperature from the alpha- tobeta-phase. The refined structure parameters are determined for both the alpha-and beta-Zn₄Sb₃.