High-temperature thermoelectric properties of the double-perovskite ruthenium oxide (Sr${}_{1-x}$La${}_x$)${}_2$ErRuO${}_6$

Abstract

We have prepared polycrystalline samples of (Sr${}_{1-x}$La${}_x$)${}_2$ErRuO${}_6$ and (Sr${}_{1-x}$La${}_x$)${}_2$YRuO${}_6$, and have measured the resistivity, Seebeck coefficient, thermal conductivity, susceptibility and x-ray absorption in order to evaluate the electronic states and thermoelectric properties of the doped double-perovskite ruthenates. We have observed a large Seebeck coefficient of -160 $\mu$V/K and a low thermal conductivity of 7 mW/cmK for $x$=0.1 at 800 K in air. These two values are suitable for efficient oxide thermoelectrics, although the resistivity is still as high as 1 $\Omega$cm. From the susceptibility and x-ray absorption measurements, we find that the doped electrons exist as Ru${}^{4+}$ in the low spin state. On the basis of the measured results, the electronic states and the conduction mechanism are discussed.

6 pages, 4 figures, J. Appl. Phys. (accepted)