Synthesis and characterization of non -stoichiometric SrTiO2.8 thermoelectric materials at high temperature and high pressure

Abstract

SrTiO3(STO) is a thermoelectric (TE) material with a wide band gap. It is usually either sintered or annealed in a reducing atmosphere to obtain semiconducting behavior. In this work, non-stoichiometric SrTiO2.8 was synthesized by the high temperature and high pressure (HPHT) method in a reducing environment to obtain improved electrical and thermal properties. The reducing environment was obtained by the application of high pressure and due to the strong ability of Ti to capture oxygen at high temperatures. The thermoelectric properties of the samples synthesized at high temperature and pressure were studied by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and UV spectroscopy. The results show that with increasing of synthesis pressure, the band gap of the samples decreases, improving their electrical properties; at the same time, the high pressure also changes the micro-morphology of the samples and improves their thermal properties. The zT value of the sample synthesized at 5 GPa reached the maximum value of 0.20 at 973 K. It was found that the mechanical strength of the synthesized samples is superior to that of the traditional alloy-based thermoelectric materials. Our work shows that HPHT provides a new variable of pressure for the optimization of the synthesis process of TE materials and provides a new approach for the synthesis and performance optimization of thermoelectric materials.