Microstructural Control and Development of Synthesis Route for Enhancing Performance of Sintered Thermoelectric Oxide Polycrystals via Chemical Solution Process

Abstract

The thermoelectric oxides, such as a p-type NaxCo2O4 and an n-type SrTiO3 etc., have been synthesized by the chemical solution process. The polymerized complex (PC) process efficiently develops compositional homogeneity of sintered polycrystals and promotes substitution of a doping element. In the case of NaxCo2O4 with a layered crystal structure, a plate-like powder precursor can be synthesized by the citric acid complex process, providing a sintered polycrystal with c-axis oriented crystallographic anisotropy. The establishment of rapid synthesis process at a low temperature of the n-type SrTiO3 system was tried by using the PC process and the pulsed current heating (PCH) method. TiB2 addition was found to be quite effective not only for reduction in the electrical resistivity, but also for rapid densification during the sintering. As a result, it was clarified that the synthesis route via the PC process, the PCH method and TiB2 addition is quite promising as a rapid synthesis process at a low temperature of the SrTiO3 system. Based on the experimental results obtained in this study, the chemical solution process is considered to be a quite effective methodology for enhancing performances of structural and functional oxides and for developing the synthesis process under soft conditions.