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.

The cubic Ba0.5La0.5CoO3‐δ was synthesized using solid state reaction. The structural properties were determined by the simultaneous refinement of Synchrotron Powder X‐ray Diffraction and Neutron Powder Diffraction data. Iodometric titration was used to examine the oxygen stoichiometry and average cobalt oxidation state. Low‐temperature magnetic studies show soft ferromagnetic character of fully oxidized material, with θP = 198(3) K and µeff = 2.11(2) µB. Electric measurements show the thermally activated nature of conductivity at low temperatures, whereas, due to the variable oxidation and spin state of cobalt, a single charge transport mechanism cannot be distinguished. Around room temperature, a wide transition from thermally activated conductivity to semi‐metallic behavior is observed. Under the inert atmosphere, the oxygen content lowers and the cation ordering takes place, leading to coexistence of two, ordered and disordered, phases. As a result of this change, thermally activated conductivity is observed also at high temperatures in inert atmosphere.

No abstract

The results of electrical conductivity studies, structural measurements and thermogravimetric analysis of La1−xTbxNbO4+δ (x = 0.00, 0.05, 0.1, 0.15, 0.2, 0.3) are presented and discussed. The phase transition temperatures, measured by high-temperature x-ray diffraction, were 480 °C, 500 °C, and 530 °C for La0.9Tb0.1NbO4+δ, La0.8Tb0.2NbO4+δ, and La0.7Tb0.3NbO4+δ, respectively. The impedance spectroscopy results suggest mixed conductivity of oxygen ions and electron holes in dry conditions and protons in wet. The water uptake has been analyzed by the means of thermogravimetry revealing a small mass increase in the order of 0.002% upon hydration, which is similar to the one achieved for undoped lanthanum orthoniobate.

Lanthanum orthoantimonate was synthesized using as olid-state synthesis method.T oe nhancet he possible protonic conductivity,s amples with the addition of 1mol %C ai nL a-site were also prepared. The structure was studied by the meanso fX-ray diffraction, which showedt hat both specimens weres ingle phase. The materials crystallized in the space group P2 1 /n. Dilatometry revealedt hat the materiale xpanded non-linearly with the temperature. The nature of this deviation is unknown; however,t he calculated linearf raction thermal expansion coefficient was 9.56 10 À6 K À1 .E lectrical properties studies showedt hat the material is ap rotonc onductor in oxidizing conditions, which was confirmed both by temperature studiesi nw et in dry air,b ut also by the H/D isotopee xchangee xperiment. The conductivity was rather modest, peakinga tt he order of 10 À6 Scm À1 at 800 8C, but this could be further improved by microstructure and doping optimization.T his is the first time protonic conductivity in lanthanum orthoantimonates is reported. Proton conducting ceramics (PCCs) are materials exhibiting ionic conductivityi nw hichp roton (H +)i sacharge carrier. [1] This class of materials has gathered interest over the years for their potential applications.E specially the so-called triple conductingo xides, that is, materials with three mobile charge carriers (protons, oxygen ions, and electron/electron holes) were discovered and studied as potential electrode materials. [2-5] The increased interest led to developing highly-efficient fuel cells [5-7] and steam electrolyzers. [8] This interest stems from the fact that PCC-based devices can operate with high efficiencies while being cost-competitive in comparison to traditional solid oxide fuel cells. [5, 9] Apart from that, new typeso fe lectrochemical devices have been developed. Such devicesc an be used for the synthesis of ammonia, [10, 11] conversion of methane into aromaticsi namembraner eactor, [12] or thermo-electrochemical production of hydrogen from methane. [13]