Environmentally friendly BaxSr2−xTiFeO6 double perovskite with enhanced thermopower for high temperature thermoelectric power generation

In the present work, the prospects of environmental friendly BaxSr2−xTiFeO6 complex double perovskites have been evaluated for applications as high temperature thermoelectric materials with properties converging to the ‘phonon-glass electron-crystal’ model. BaxSr2−xTiFeO6 compositions with 0.0 ≤ x ≤ 0.25 were synthesized by a solid-state reaction method. The oxide samples were then investigated for their crystal structure (single phase) and morphology by XRD and SEM, respectively. Thermo-power or Seebeck coefficient (S) and the electrical conductivity (σ) of these oxide samples were simultaneously measured to calculate the thermoelectric power factor (S2σ). All the BaxSr2−xTiFeO6 compositions showed p-type non-degenerate semiconductor behavior before semiconductor to metal transition occurred as evident from the temperature dependent Seebeck coefficient of these double perovskites. Conduction mechanisms of these oxides were analyzed using variable range hopping and small polaron hopping conduction models. All these double perovskites exhibited more than 100 μV K−1 thermo-power in the wide range of temperature from 300 K to 1223 K. A very high thermo-power (S) value (∼800 μV K−1) was obtained for BaxSr2−xFeTiO6 with x = 0.25 at 1123 K.