Improvement of thermoelectric properties of xNb:(1-x)SrTiO3 composite ceramics by high-pressure high-temperature synthesis

The high stability and low cost are considered comparative advantages of the SrTiO3 chalcogenide oxide thermoelectric material. However, the pure SrTiO3 material is characterized by low electrical conductivity and high thermal conductivity, which could eventually lead to poor overall thermoelectric performance, and limit its application in the field of high temperature thermoelectricity. The development of composite-based metal materials with SrTiO3 by using suitable methods is arising as the most promising approach to improve their electrical properties. Along these lines, in this work, xNb:(1-x) SrTiO3 composite ceramics were successfully synthesized by using the high temperature and high-pressure (HPHT) method. The Nb powder was oxidized into various niobium oxides exhibiting their own thermoelectric properties under HPHT conditions to optimize the thermoelectric properties of the Nb/SrTiO3 composites. From our analysis, it was demonstrated that with the increase of the Nb powder content, the electrical properties were significantly improved. In addition, the fabricated Nb/SrTiO3 composite ceramics possessed a special "pore" microstructure, which significantly reduced the thermal conductivity of the material. In this work, the physical phase, microscopic morphology, and thermoelectric properties of the synthesized samples were also systematically tested and analyzed, and the maximum zT value of 0.28@973 K was obtained for the final sample with x = 0.4. The implementation of the HPHT method for the preparation of chalcogenide oxide composite ceramics provides valuable insights for the improvement of their thermoelectric properties.