Liquid phase sintering of Nb doped SrTiO3-δ ceramics with enhanced thermoelectric figure of merit

Abstract

SrTiO3 (STO) based ceramics are a promising n-type semiconductor oxide for high-temperature thermoelectric application. In the present work, the results of liquid-phase sintering (LPS) aid incorporating various concentrations of Al2O3, CuO and ZnOin Nb-doped STO (STN) is presented. With the inclusion of sintering aid, densities comparable to those obtained by conventional sintering (greater than 97%) were achieved for samples sintered as low as 1623 K. We also report the effect of various sintering aid (Al2O3, CuO, and ZnO) with different concentrations (1–5 wt %) on the thermoelectric figure of merit ZT of Nb-doped SrTiO3 (STN) ceramics. SEM images provided evidence of the presence of the low-temperature liquid phase around the grain boundaries of STN ceramics. The dislocations caused by liquid phase formation remove densification issues and enhances thermoelectric properties. A simultaneous increase in both electrical conductivity and the Seebeck coefficient was observed when the sintering aid concentration increased. The maximum electrical conductivity value of 390 Scm−1 at 420 K was obtained for the 5 wt % CuO added STN (STNCu5) ceramics, which was about two orders higher than the pristine STN sample sintered at that temperature. The highest PF value of 1040 Wm−2K−2 resulted in a remarkable ZT value of ≈0.4 (0.38) at 573 K for 5 wt % Al2O3 added STN (STNAl5) ceramics at a very low sintering temperature. To our knowledge, the LPS strategy is a completely novel approach in STO-based ceramics for thermoelectric applications.