Structure and thermoelectric transport properties of isoelectronically substituted (ZnO)(5)In2O3

We have proposed that homologous compounds of (ZnO)(n) In2O3 with layer str uctures can become candidate materials for high-temperature thermoelectric conversion due to their low thermal conductivity and high electron mobility . Crystal structures can be modified by the isoelectronic substitution of e ither divalent or trivalent metal ions for Zn or In ions, respectively. Sub stitution of Mg2+, Co2+, and Y3+ gave rise to shrinkage of the c axis and e longation of the n axis of a hexagonal unit cell. Rietveld structure refine ment indicated that Mg2+ and Co2+ ions occupy both 3a and 6c sites, while Y 3+ ions occupy only 3a sites. An optimum amount of substitution of these ca tions increased electron mobility and hence thermoelectric efficiency Z = s igma alpha(2)/kappa (sigma = electrical conductivity, alpha = Seebeck coeff icient, kappa = thermal conductivity). Z values coupled with lowered therma l conductivity, which,vas possibly caused by suitable modification of the e lectronic structure, were associated with distortion of the crystal structu re. For instance, the figure of merit of (ZnO),(In0.97Y0.03)(2)O-3 was Z = 1.3 x 10(-4) K-1. (C) 2000 Academic Press.