Thermoelectric properties of double-perovskite oxide Sr_2-xM _xFeMoO₆ [M = Ba, La)

Doping effects for the A-site in double-perovskite type oxide Sr _2-xM_xFeMoO₆ (M = Ba, La) are investigated on the thermoelectric properties of the oxides. The Seebeck coefficient, S, shows that all the samples of both Ba- and La-doped Sr₂FeMoO₆ systems are n-type over the measured temperature range. In particular, the power factor, S² σ, of the Sr₂FeMoO₆ system largely increased with increasing Ba doping level up to x = 0.3. As a consequence, S² σ of Sr_1.7 Bao _0.3FeMoO₆ reached ca. 0.8 × 10^-4 W/mK², the largest value of all the samples in this study. The thermal conductivity, κ, shows a general trend in which the value decreases from ca. 1 W/mK at room temperature to ca. 0.7 W/mK at 1100 K. The dimensionless figure of merit, ZT, of the Badoped samples increased with increasing Ba doping level. Moreover, the ZT value drastically increased above 700 K due to the S² σ value increasing above 700 K and the κ value decreasing monotonically. As a result, the ZT value of Sr _1.7Ba_0.3FeMoO₆ reached 0.31 at 1100 K.