IMF2017

In this work, thermoelectric property of double perovskite Ba_xSr_2-xTiCoO₆(BSTC) materials has been studied. Ba_xSr_2-xTiCoO₆ for 0 ≤ x ≤ 0.2 ceramic samples were synthesized by solid-state reaction route. Phase purity, crystal structure and elemental composition were confirmed by XRD and SEM/EDS respectively for those samples. Average grain size, grain orientation and distribution were investigated by EBSD. Dielectric measurements were carried out for all BSTC samples in the range of 10 K - 700 K. Frequency dispersion behavior in the dielectric constant and dielectric lost curve suggested the relaxor behavior in samples. Seebeck coefficient and electrical conductivity of BSTC were measured in the temperature range of 300 K to 1273 K. Maximum value of Seebeck coefficient achieved was 345 µV/K at 1222 K for BSTC with x = 0.15 and positive Seebeck coefficient which indicate p-type semiconductor behavior. Thermal conductivity of BSTC samples was measured in the temperature range of 300 K to 1250 K. Thermal conductivity of all BSTC samples varied from 0.01 W/mK to 0.55 W/mK. Maximum dimensionless TE figure-of-merit ZT obtained was 0.29 at 1223 K for BSTC composition with x = 0.2. Further p-type behavior of samples was confirmed by X-ray Photoelectron Spectroscopy (XPS). It happens due to variation in oxidation state of Ti and Co both. We have shown that dipolar glassy phase induced by relaxor ferroelectric in BSTC results in low thermal conductivity. Hence a very good figure of merit ZT values was obtained.