IMF2017

Double perovskite materials have interesting structural, electronic and magnetic properties which have driven the researchers to study the thermoelectric material properties of such materials for efficient and clean energy conversion. In this work Sr has been substituted by La and Ca separately to check its effect on the thermoelectric properties of Sr₂TiFeO₆ double perovskite. Crystal structure of these double perovskites have been determined as Pm-3m space group by rietveld refinement of XRD data. Microstructure was investigated by SEM. The electrical conductivity of these oxides exhibit a semiconductor (dσ/dT > 0) to metal (dσ/dT < 0) transition behaviour for all the compositions. Further the conduction mechanism of these oxides were studied with respect to polaron hopping model and non-degenerate semiconductor model was used to calculate the activation energy associated with carrier generation. Both La_xSr_2-xTiFeO₆ (LSTF) Ca_xSr_2-xTiFeO₆ (CSTF) composition exhibit p-type to n-type conductivity switching at elevated temperature. Moreover, this accompanied by a large change in thermopower with 2516 µW/mK² for La_0.1Sr_1.9TiFeO₆ and 4239 µW/mK² for Ca_0.2Sr_1.8TiFeO₆. A colossal change in thermopower associated with p–n type conduction switching driven by temperature in the same oxide compound provides a great potential to develop next generation, high temperature multifunctional electronic devices like switches,diodes, thermistors, etc.