Structural Properties and Water Uptake of SrTi(1−x)Fe(x)O(3−x/2−δ)

In this work, Fe-doped strontium titanate SrTi(1−x)Fe(x)O(3−x/2−δ), for x = 0–1 (STFx), has been fabricated and studied. The structure and microstructure analysis showed that the Fe amount in SrTi(1−x)Fe(x)O(3−x/2−δ) has a great influence on the lattice parameter and microstructure, including the porosity and grain size. Oxygen nonstoichiometry studies performed by thermogravimetry at different atmospheres showed that the Fe-rich compositions (x > 0.3) exhibit higher oxygen vacancies concentration of the order of magnitude 10(22)–10(23) cm(−3). The proton uptake investigations have been done using thermogravimetry in wet conditions, and the results showed that the compositions with x < 0.5 exhibit hydrogenation redox reactions. Proton concentration at 400 °C depends on the Fe content and was estimated to be 1.0 × 10(−2) mol/mol for SrTi(0.9)Fe(0.1)O(2.95) and 1.8 × 10(−5) mol/mol for SrTi(0.5)Fe(0.5)O(2.75). Above 20 mol% of iron content, a significant drop of proton molar concentrations at 400 °C was observed. This is related to the stronger overlapping of Fe and O orbitals after reaching the percolation level of approximately 30 mol% of the iron in SrTi(1−x)Fe(x)O(3−x/2−δ). The relation between the proton concentration and Fe dopant content has been discussed in relation to the B-site average electronegativity, oxygen nonstoichiometry, and electronic structure.