Effect of B-site cation ordering on high temperature thermoelectric behavior of BaxSr2-xTiFeO6 double perovskites.

Abstract

Here, we have reported the detailed structural analysis in correlation with thermoelectric properties of Ba doped Sr2TiFeO6 (BSTF) double perovskites in the temperature range from 300 K to 1100 K. BSTF compositions exhibit single phase cubic structure with Pm3 ̅m crystal symmetry from room temperature to 523 K and also at temperature beyond 923K. Rietveld refinement of high temperature XRD data suggests the coexistence of two cubic phases with Pm3 ̅m space group having same composition in the intermediate temperature region. Correlation of the phase-fraction with electrical conductivity data posits the possibility of high temperature cubic phase being conductive compared to the insulator-like cubic phase observed at room temperature. The experimental analysis alone seems insufficient to explain the conductivity behavior demonstrating semiconductor (dσ⁄dT>0) to metal like (dσ⁄dT<0) transition. Hence DFT framework has been adopted for computational analysis coupled with the Boltzmann transport equations to understand their thermoelectric properties based on the electronic restructuring occurred due to octahedral arrangements in these double perovskites. It has been shown that clustering of FeO6 octahedra may lead to the formation of a conduction path in the cubic phase of BSTF, which induces metallic behavior in these double perovskites.