Improving thermoelectric performance of SrTiO3 by isovalent Zr substitution doping

Thermoelectric materials based on SrTiO 3 are low in cost and environmentally friendly, but their performance must be further improved for practical application. In this study, we show that isovalent substitution of the B-site Ti 4+ in a La doped SrTiO 3 (LSTO) matrix is both effective in reducing thermal conductivity and improving power factor ( PF ). In brief, Zr 4+ substituted LSTO (La 0.08 Sr 0.9 Ti 1- x Zr x O 3 ; x  = 0, 0.02, 0.04, and 0.06; labeled as LSTO-Zr 0.02 , LSTO-Zr 0.04 and LSTO-Zr 0.06 , respectively) are prepared by solid-state-reaction and densified in a reducing environment. The optimized LSTO-Zr 0.02 shows a 30 % increase in PF and 12 % reduction in thermal conductivity compared with that of LSTO. Particularly, the LSTO-Zr 0.06 sample with highest substitution level has the largest reduction in thermal conductivity compared to the LSTO matrix (30 %, from 8.2 to 5.6 W m −1 K −1 at 300 K). The reduction in thermal conductivity is because the Zr 4+ substitution introduces chemical impurities and lattice defects, benefiting the scattering of phonon thermal carriers. The improvement in PF after Zr substitution is attributed to the enhanced Seebeck coefficient because of the slightly reduced carrier concentration. In contrast to the B-site Ti 4+ cations, which are partially reduced to Ti 3+ under the reducing environment and contribute to electron carriers, the Zr 4+ are not reduced, resulting in lower electron carrier concentrations after Zr 4+ substitution. This isovalent substitution strategy provides a potential route for the development of high-performance thermoelectric materials based on SrTiO 3 .