Structure and thermoelectric properties of Ca2-xSrxFeMoO6 (0 ≤ x ≤ 0.3) double-perovskite oxides

The thermoelectric properties of double perovskite-type oxides Ca2FeMoO6 are investigated in terms of Sr substitution at the A site of the oxides. The electrical conductivity, sigma, of Ca2-xSrxFeMoO6 (0 <= x <= 0.3) showed a metallic behavior, decreasing monotonically from ca. 10(3) S cm-1 at room temperature to ca. 10(2) S cm(-1) at 1250K. At room temperature, although the sigma values of the oxides increased with increasing substitution level, x, the sigma values maintained almost the same values at high temperature range of 1000-1250K. The absolute values of the Seebeck coefficient, S. for the samples at x < 0.3 abruptly increase at around 1000 K. The Rietveld refinement of the XRD patterns of the oxides indicated that the anti-site defects in the oxides decreased with increasing Sr concentration. The power factor, S-2 sigma, of the oxides largely increased with increasing temperature; the S-2 sigma value of Ca2FeMoO6 was ca. 0.35 mWmK(-2) at 1200K, the largest value of all the samples in this study. Although the thermal conductivity. K, of the oxides generally decreased from ca. 3.5 to 4.5W mK(-1) at room temperature to ca. 2-3W mK(-1) at 1050K, the sample at x = 0.3 showed the lowest and most T-independent K values, implying that the relative increase in the temperature is independent from the phonon-impurity scattering caused by the A-site substitution. The power factor of the oxides increased above 900 K; thereby, the dimensionless figure of merit, ZT =(S-2 sigma/kappa)T, significantly increased at the same temperature range. The largest ZT value of 0.15 was observed for Ca2FeMoO6, Ca1.9Sr0.1 FeMoO6, and Ca1.8Sr0.2FeMoO6 at 1250K. (C) 2012 Elsevier B.V. All rights reserved.