Influence of sintering conditions on microstructure and electrical conductivity of yttrium-substituted SrTiO3

The microstructure and electrical conductivity of Y-substituted SrTiO3 ceramics (Sr1−αxYxTiO3−δ, x = 0, 0.035, 0.07; α = 1.0, 1.5) sintered under both oxidizing and reducing conditions were studied in detail. In these compositions, Y3+ ions have been found to occupy the Sr sites and act as donor substitutes. The observed interesting dependence of the microstructure and electrical property on the starting composition (cation nonstoichiometry) and the sintering or processing conditions indicates that the defect chemistry known for other donor-substituted SrTiO3 (e.g. Sr1−xLaxTiO3−δ) ceramics also applies for Y-substituted SrTiO3 ceramics. The positive charge from the Y-substitute can be compensated either electronically under reducing conditions or ionically under oxidizing conditions. Therefore, to obtain a single-phase and highly conductive yttrium-substituted SrTiO3 material, e.g. as a candidate for an SOFC anode, a starting composition with (Sr + Y)/Ti = 1 and a high-temperature heat treatment (>1200 °C) under reducing conditions is required.