Here, for the first time, we present data on proton conductivity of high-entropy, single-phase perovskites. The BaZr0.2Sn0.2­Ti0.2Hf0.2Ce0.2O3−δ, BaZr0.2Sn0.2­Ti0.2Hf0.2­Y0.2O3−δ, BaZr1/7Sn1/7­Ti1/7Hf1/7­Ce1/7Nb1/7Y1/7O3−δ, and BaZr0.15Sn0.15­Ti0.15Hf0.15­Ce0.15Nb0.15­Y0.10O3−δ single-phase perovskites were synthesized. Before electrical measurements, materials were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and thermogravimetric analysis (TGA). The following experimental results demonstrated that studied high-entropy perovskites are proton conductors: (1) The observed mass increase upon the switch from dry to wet atmosphere confirmed the water incorporation into materials structure. (2) The electrochemical impedance spectroscopy (EIS) revealed that the total conductivity increased while its activation energy decreased in the presence of water vapor in the atmosphere. (3) The conductivity in atmosphere humidified with H2O and D2O differed one from another, showing typical of proton conductors isotope effect in high-entropy oxides.

The structure and thermomechanical properties of As-substituted lanthanum orthoniobates are presented and an in-depth analysis of a broad range of other substituents is performed.

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.

In this work, lanthanum orthoniobates doped with either antimony, calcium, or both have been synthesized and studied. The water uptake of the investigated materials has been analyzed by means of thermogravimetric studies. The results show the difference between the thermodynamics of hydration between the lanthanum orthoniobate system and other proton conducting ceramics. The relation between the water uptake and effective acceptor doping for the investigated system has been found, and the energetics of the water uptake relation are discussed.