Thermoelectric Properties of Highly Textured Ca-Doped (ZnO)_<i>m</i>In₂O₃Ceramics

Abstract

Highly textured Ca-doped (ZnO)mIn2O3 (m is an integer) ceramics were fabricated by the reactive templated grain growth (RTGG) method and their thermoelectric properties were examined. Platelike ZnSO4·3Zn(OH)2 particles were used as reactive templates and mixed with In2O3 and CaCO3 powders into a stack of tapes. In situ formation and subsequent sintering resulted in textured Ca-doped (ZnO)mIn2O3 ceramics. The electrical conductivity of the textured specimen along the ab-plane was almost two times larger than that of the textured specimen along the c-axis and about 30% larger than that of a nontextured specimen. On the other hand, the Seebeck coefficients of the textured specimen exhibited a small anisotropy. The thermal conductivity of the RTGG specimen along the ab-plane was higher than that of the RTGG specimen along the c-axis. However, both specimens showed similar values at high temperatures. As a result, the Ca-doped specimen along the ab-plane with a composite phase of (ZnO)3In2O3 and (ZnO)4In2O3 showed a ZT value of 0.31 (at 1053 K), compared with 0.23 (at 1053 K) for the nontextured specimen.