High-temperature thermoelectric properties of the compound CaAl2Si2 and effects of substitution and doping

Kurzfassung

Zintl phases are promising thermoelectric materials especially because of their so-called ‘electron crystal, phonon glass’ behaviour[1]. This work focuses on high temperature thermoelectric properties of the ternary 1-2-2 Zintl phases Ca1-xAxAl2-yMySi2 (A = Sr, Ba; M = Zn, Mn)[2]. Compounds with the CaAl2Si2 structure type are known to be interesting thermoelectric materials, an example is CaZn2Sb2 [3]. Low-temperature measurements (10-300 K) of the thermoelectric properties for CaAl2Si2 were recently described[4]. We were interested in the thermoelectric potential of compounds with the general composition Ca1-xAxAl2-yMySi2. Synthesis of the materials was done via arc melting technique. The samples were characterized, densified (hot pressing, SPS) and investigated with respect to their thermoelectric properties (compare [5]). Characterization methods include X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Furthermore high temperature thermal analysis, Seebeck, electrical and thermal conductivity measurements were done. The results will be discussed as well as the influence of the compositional variation of x and y. While substitution with an alkaline earth metal should reduce the thermal conductivity, doping aluminium with zinc or manganese should have an effect on the electrical properties of the material since the conductivity is present mainly in the Al2Si2 layers. [1] G. A. Slack, in CRC Handbook of Thermoelectrics, ed. D. M. Rowe, CRC Press, New York, 1995, 407-440. [2] C. Kranenberg, D. Johrendt, A. Mewis, Z. Anorg. Allg. Chem. 1999, 625, 1787. [3] E. S. Toberer, A. F. May, B. C. Melot, E. Flage-Larsen, G. J. Snyder, Dalton Trans. 2010, 39, 1046. [4] Y. K. Kuo, K. M. Sivakumar, J. I. Tasi, C. S. Lue, J. W. Huang, S. Y. Wang, D. Varshney, N. Kaurav, R. K. Singh, J. Phys.: Condens. Matter 2007, 19, 176206. [5] M. Möller, G. Cordier, K. Hofmann, B. Albert, Z. Anorg. Allg. Chem. 2012, 638, 1637.