Structural Properties and Water Uptake of SrTi1−xFexO3−x/2−δ

Abstract

In this work, Fe-doped strontium titanate SrTi1−xFexO3−x/2−δ, for x = 0–1 (STFx), has been fabricated and studied. The structure and microstructure analysis showed that the Fe amount in SrTi1−xFexO3−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 1022–1023 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 SrTi0.9Fe0.1O2.95 and 1.8 × 10−5 mol/mol for SrTi0.5Fe0.5O2.75. 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 SrTi1−xFexO3−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.

Structure and water uptake in BaLnCo2O6−δ (Ln =La, Pr, Nd, Sm, Gd, Tb and Dy)

“…The comparison between La-based compounds (Figure 10.b) indicates that the ordered structure exhibits four times larger uptake than the disordered phase. The weight gain is slow, and not apparently reversible upon changing the atmosphere back to dry air, as would be expected in isothermal hydration/dehydration [33][34][35].…”

Structure and transport properties of triple-conducting BaxSr1−xTi1−yFeyO3−δoxides

“…Such behaviour was previously observed for perovskite materials, where the increase of the water uptake was connected with an increase of the basicity of cations. 21,24,28,29 Proton is bonded to oxygen belonging to the B-O bond, however, the role of the A-cation is important. For perovskites (ABO 3 ), the inuence of electronegativity of the A cation on the B-O bond was previously observed.…”

“…The highest proton concentration was found in SrTi 0.9 Fe 0.1 O 2.8Àd at 400 C. In this sample, the proton concentration was estimated as 5.2 Â 10 À2 mol mol À1 , whereas in the samples with higher iron content the proton concentration was lower. 24 To improve the water uptake for ABO 3 materials, additional dopants at A-and B-sites should be introduced. Such substitutions were previously introduced for SrFeO 2.5 , where both the A-site and B-site various dopants were investigated in terms of hydration of the samples.…”

“…was switched into the humidied synthetic air (p H 2 O z 10 À2 atm.). The difference between the masses recorded in the dry and wet atmospheres at 300 C (Dm H 2 O ) allowed to estimate the molar protonic defect concentration ½OH O .O is given by equation:24…”

Microstructural Design of Ba0.5La0.5Co0.5Fe0.5O3 Perovskite Ceramics

“…Certainly more studies are required to prove such a hypothesis, but several factors support it. First of all, water uptake was observed in many Ba-based cobaltites and ferrites with perovskites structures [16,20,33,34]. Most importantly, proton formation was observed in Ba 0.5 La 0.5 CoO 3−δ [16], which is a Fe-free equivalent of BLCF.…”