Perovskite materials in the CaTiO₃-SrTiO₃ system doped with different amounts of iron (1, 2 and 5 mol.%) and various Ca/Sr ratios were prepared by the modified citrate method. Additionally, the materials with 0.05 deficiency in strontium/calcium sublattice and 5 mol.% of Fe were also synthesised. The materials were subjected to structural (XRD, XANES) and microstructural (SEM) characterisation, as well as the analysis of susceptibility to reduction/oxidation processes. The structural analysis indicates a lack of iron-containing phases; thus, an incorporation of Fe into the perovskite structure was postulated. Additionally, the oxidation state of iron in the perovskite structure changes with the dopant amount. The temperature-programmed reduction measurements showed partial reversibility of the reduction processes. For the materials with the highest iron amount, the catalytic tests in NH₃-SCO and NH₃-SCR reactions were carried out. The materials showed high catalytic activity and high selectivity to N₂ in the NH₃-SCR process; however, they were inactive in NH₃-SCO.

Manganese-doped (Mn/Ti = 0.02/0.98) SrTiO₃-based materials with various Sr/Ti mole ratios (1.02, 1.00, 0.97 and 0.92) were obtained by the citrate precursor method. The materials were characterised in terms of microstructure (SEM), structure (XRD, XANES), electrical properties (DC method) and reducibility (TPR). With the introduction of 2 mol.% Mn, the cubic structure of SrTiO₃ is preserved, but significantly limits (from Sr/Ti ≥ 0.8 to Sr/Ti > 0.92) the possibilities of deviations from stoichiometry at 1200°C. The narrowing of the stability limit of the perovskite structure to Sr/Ti > 0.97 with an increase in temperature to 1400°C and segregation of Ti-Mn-enrich species are shown. The location and the oxidation states of Mn in both (Sr and Ti) sublattices depend on the assumed Sr/Ti ratio and sintering temperature. Regardless of the Sr/Ti ratio, Mn-doped SrTiO₃ exhibits very low electrical conductivity with an ionic conductivity mechanism. Graphical abstract