Thermoelectric properties of filling-controlled zinc-antimonides with layer structure

Thermoelectric properties have been investigated for polycrystalline samples of layer-structured $R_{1-x}A_x$ZnSbO ($R$=La, Ce; $A$=Ca, Sr) as two-dimensional analogues of a conventional thermoelectric semiconductor ZnSb[1]. By substituting $A^{2+}$ for $R^{3+}$ in the charge-reservoir layers, carrier concentration can be successfully controlled without lowering the carrier mobility. The hole doped materials showed low thermal conductivity and moderately high thermopower, whose temperature- and doping-dependence were well explained by theoretical calculation. The values of dimensionless figure of merit $ZT$ were found to increase without showing any sign of saturation up to 390 K, and even higher values can be expected along the conducting ZnSb layers for a single crystal. These results indicate the potential of the hole-doped $R$ZnSbO as a good thermoelectric material. This work was in part supported by FIRST program on \lq\lq Quantum Science on Strong Correlation\rq\rq \ from JSPS. \\[4pt] [1] T. Suzuki, M. S. Bahramy, R. Arita, Y. Taguchi, and Y. Tokura, Phys. Rev. B 83, 035204 (2011)