Effect of Ba-doping on high temperature thermoelectric properties of Sr2TiMoO6 double perovskites

Abstract

Abstract Oxides based thermoelectrics have the advantage over other materials due to their low processing cost, better temperature stability and environmental friendly nature. However, it is difficult to achieve good electrical conductivity along with high Seebeck coefficient in oxides. Recently double perovskites based oxides have shown great potential to optimize various thermoelectric (TE) parameters in order to achieve high figure-of-merit, ZT values for TE power generations. In the present work we investigated the effect of Ba-doping on the high temperature thermoelectric properties of double perovskite Sr 2 TiMoO 6 (STM), which exhibits metal like conductivity (∼10 5 S/m). Dense ceramic samples of Ba x Sr 2-x TiMoO 6 with 0 ≤ x ≤ 2.0 were synthesized using solid-state reaction route. Rietveld refinement of XRD data confirmed the cubic crystal structure in these double perovskites with space-group P m 3 ¯ m . It is shown in this paper that complete substitution of barium in place of strontium actually increases the Seebeck coefficient without compromising much in electrical conductivity values, resulting better thermoelectric power factor in Ba 2 TiMoO 6 (BTM) compared to STM composition. Thermopower (S) measurement showed the conductivity switching from p-type to n-type behavior in all the compositions at higher temperature although the switching temperature decreases with increase in Ba-concentration. Temperature dependent Seebeck coefficient was further explained using an analytical model for coexistence of both types of charge carriers in these oxides. Conductivity mechanism of these double perovskites was found to be governed by small polaron hopping model.