Role of First-Row d-Block Metals in Shaping the Properties of Nonstoichiometric SrTiO3

The A-site nonstoichiometry in doped ABO3 perovskites is typically introduced to tailor the materials' functional properties through defect engineering and to promote dopant exsolution. In this work, the redox behavior and electrical properties of 5 mol % Sr-deficient strontium titanate doped with the first-row d-block elements (Mn, Fe, Co, Ni) were investigated to elucidate the relationships between dopant characteristics and the resulting properties of the final materials. The materials were sintered at 1200 °C and 1400 °C to obtain samples with significantly different microstructures. The results indicate that although the B-O bond energy contributes to the overall physicochemical behavior of the investigated materials, the properties of SrTiO3-based systems are generally shaped by the nature of the dopant and, more specifically, by its intrinsic characteristics. In Fe- and Ni-doped materials, the key factor is the ability of these cations to be exsolved as metallic particles under reducing conditions. In Co-containing materials, the physicochemical behavior is strongly affected by the volatility of cobalt species at high temperatures. In contrast, Mn-doped systems are mainly influenced by temperature-dependent site preferences of Mn ions, which can occupy both the Sr and Ti sublattices.