Enhanced reducibility and conductivity of Na/K-doped SrTi0.8Nb0.2O3

Abstract

Donor and acceptor co-doped SrTiO₃ materials have shown interesting features in their conductivity and reducibility. In this work, 10 mol% Na⁺ or K⁺ as acceptor dopants have been introduced into the A-site of donor-doped strontium titanate, SrTi_0.8Nb_0.2O₃, and the doping impact on their properties has been studied. By doping with Na or K, the sinterability of SrTi_0.8Nb_0.2O₃ in reducing atmospheres has been improved. Na_0.1Sr_0.9Ti_0.8Nb_0.2O₃ and K_0.1Sr_0.9Ti_0.8Nb_0.2O₃ show metallic conduction behavior after being sintered at 1400 °C in 5% H₂/N₂. Electrical conductivity reaches 1180 S cm⁻¹ at 400 °C and 272 S cm⁻¹ at 800 °C for K_0.1Sr_0.9Ti_0.8Nb_0.2O₃, which is higher than that of Sr_0.99Ti_0.8Nb_0.2O₃ prepared under similar conditions, indicating the improved reducibility of acceptor doped SrTi_0.8Nb_0.2O₃. Such improvement may be attributed to the improved oxide ionic conductivity and cation mobility at high temperatures. Reduced polarization resistance is also observed using Na_0.1Sr_0.9Ti_0.8Nb_0.2O₃ and K_0.1Sr_0.9Ti_0.8Nb_0.2O₃ as anodes on YSZ electrolytes, suggesting improved catalytic activity by Na/K-doping.