IMF2017

Recently oxides have been used as thermoelectric materials with a good combination of several parameters such as high Seebeck coefficient, good electrical conductivity and low thermal conductivity. Oxides materials, in general, demonstrate high Seebeck coefficient, however they suffers from low electrical conductivity. Hence, electrical conductivity of oxide materials need to be improved for developing efficient thermoelectric devices. In the present work, the thermoelectric properties of La and Ba doped Sr₂TiMoO₆ (STM) double perovskites have been studied. Polycrystalline samples of these double perovskites have been synthesized by solid-state reaction process. Sintering has been done at 1573 - 1673 K under reducing atmosphere. X-ray diffraction has confirmed single phase solid solution. Seebeck coefficient and electrical conductivity have been measured from room temperature to 1273 K. These compounds have high electrical conductivity in the range of 10⁴ - 10⁵ S/m at room temperature and have large carrier concentrations (~10²²/cm³) which are generally found in metals. These oxides exhibit p-type to n-type conduction switching at higher temperature. To evaluate the source of charge carries and oxidation state of cations in these double perovskites XPS measurement has been carried out. Temperature dependent Seebeck coefficient has been explained using an analytical model for coexistence of high mobility electrons and low mobility oxygen vacancies in these oxides. Conductivity mechanism of these double perovskites has been found to be governed by small polaron hopping model.