The single-phase Pr1-xBaxCoO3-delta (0 < x <= 1/3) ceramic oxides were successfully synthesized using the standard ceramic technique. They possess an orthorhombic Pbnm structure at room temperature after cooling in air. However, an orthorhombic (Pbnm) -> rhombohedral (R<(3)over bar>c) phase transition occurs in Pr1-xBaxCoO3-delta upon heating in air. The spin state transition of cobalt ions contributes significantly to the thermal expansion of Pr1-xBaxCoO3-delta with low barium content (x <= 0.1) between room temperature and around 450 degrees C. The temperatures of structural and spin state transitions depend on the Ba content. In addition, oxygen exchange at high temperatures causes noticeable chemical expansion of Pr1-xBaxCoO3-delta. By analyzing the thermochemical expansion and nonstoichiometry data for Pr1-xBaxCoO3-delta, both measured in air, we proposed and verified a novel approach to evaluating the defect structure and thermodynamics of defect equilibria in oxide ceramic materials. The obtained defect structure model was shown to predict accurately the experimental pO(2)-T-delta data of Pr1-xBaxCoO3-delta perovskites.

For three perovskites from the Sr(Ti,Fe)O3-delta (STF) system-SrTi0.7Fe0.3O3-delta (STF30), SrTi 0.5 Fe 0.5 O 3-delta (STF50), and SrTi 0.3 Fe 0.7 O 3-delta (STF70)-the enthalpy of oxidation, Delta H ox , measured by Calvet calorimetry, was found to be an almost temperature-independent function of delta . The data on Delta H ox ( delta ) allowed subtracting the redox contribution from the drop calorimetric measurement results, yielding the enthalpy increments of STF with fixed oxygen content. The heat capacities of these STF oxides were successfully described by the single Einstein term, with the fitted Einstein temperatures depending almost linearly on titanium content. The additional dilatometric and thermogravimetric measurements were used to estimate the thermal (TEC) and chemical expansion coefficients of STF. While TEC somewhat decreases with titanium content, the chemical expansion remains rather high for all STF. Finally, the obtained thermochemical data were used to compare the energy and oxygen storage capacities of different STF with those of undoped strontium ferrite; both were found to decrease noticeably with titanium substitution. Hence, in applications such as chemical looping, e.g., in solar energy conversion and storage, the STF with lower titanium content would possess better functional properties, although they might be less chemically stable than titanium-rich STF oxides.

Standard enthalpies of formation at 298.15 K, Delta fH degrees 298.15, for RCoO3-delta (R = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y) perovskite-type rare-earth cobaltites were obtained from the combined results of drop and reduction calorimetry. The relationship between the oxygen nonstoichiometry, delta, and thermodynamics of RCoO3-delta was discussed. The fact that RCoO3-delta with smaller ionic radius of R3+ tend to be less stable, having more positive enthalpy of formation from binary oxides (CoO and R2O3), Delta f,oxH degrees 298.15, was confirmed for all the studied RCoO3-delta. Drop calorimetry results were also used in discussing, comparing and assessing the literature heat capacity, Cp(T), data for RCoO3-delta (R /= Y). For YCoO3-delta, both Delta fH degrees 298.15 and Cp(T) were obtained for the first time solely from the drop calorimetric results; Delta fH degrees 298.15 values determined by two different methods perfectly agree with each other. The reference data and Cp(T) of RCoO3-delta were used to calculate Delta fH degrees 298.15 from the published EMF measurement results so as to compare the available Delta f,oxH degrees 298.15(RCoO3-delta) values. An unusual dependence of Delta fH degrees 298.15(LaCoO3-delta) on its heat treatment history was identified and supported by the additional isoperibolic solution calorimetry measurements.

The crystal structure of Ba(Ce0.7Zr0.1Y0.1Yb0.1)O3–δ was studied depending on temperature in dry and wet atmosphere using in situ high temperature X-ray powder diffraction. Phase transition from tetragonal I4/mcm to cubic Pm-3m structure was shown to occur in Ba(Ce0.7Zr0.1Y0.1Yb0.1)O3–δ upon heating from 25 up to 1000 °C irrespective of air humidity. The cubic Pm m and tetragonal I4/mcm phases possess comparable coefficients of linear thermal expansion (CTEs), 10.6·10–6 K–1. Even in very dry atmosphere (10–4 atm H2O), chemical expansion caused by hydration contributes significantly to the observed structural transformations and the variation of the unit cell parameters of Ba(Ce0.7Zr0.1Y0.1Yb0.1)O3–δ.

Perovskite-type oxides BaZr1–xYxO3−x/2 (x = 0.1, 0.2) were synthesized and their enthalpy increments were measured by means of high-temperature drop calorimetry in the temperature range of (373–1273) K in air. The data obtained were used for estimating the high-temperature thermodynamic functions (constant pressure heat capacity and entropy increments) of the zirconates BaZr1–xYxO3−x/2 (x = 0.1, 0.2). They were found to be only weakly dependent on the concentration of Y-dopant. Thermal expansion coefficient of zirconates BaZr1–xYxO3−x/2 (x = 0.1, 0.2) was successfully estimated by Grüneisen equation. Also, Neumann-Kopp rule was shown to be inapplicable for accurate estimation of heat capacities of the studied oxides. Thermodynamic analysis showed that BaZr1–xYxO3−x/2 (x = 0.1, 0.2) oxides are prone to chemical interaction with CO2 at typical working temperatures of proton-conducting solid oxide fuel cells. Some possibilities to overcome this issue have been discussed.

Proton-conducting electrolytes (PCEs) are extensively researched materials utilized in solid oxide electrochemical cells with various operating principles. The high ionic (protonic) transport of PCEs offers superior performance of such cells at reduced temperatures (400-600 degrees C). However, chemical-related deformations (strains) caused by the materials' hydration/dehydration pose serious technological challenges for fabricating multilayered (cer-cer, cer-met, and cer-glass) assemblies. Therefore, studying both thermal and chemical expansions of PCEs is crucial. This work presents in-depth high-temperature characterization of Sc-doped BaSnO3 compounds (BaSn1-xScxO3-delta) in terms of their thermochemical expansion behavior. This characterization includes high-temperature X-ray diffraction and dilatometry analyses under various measuring conditions. On one hand, the collected data can serve as technological characteristics for the selection of appropriate functional materials. On the other hand, the thermochemical expansion data can be used to evaluate the thermodynamic parameters (enthalpy and entropy of hydration) and transport parameters (water chemical diffusion coefficient and chemical surface exchange constant) of PCEs. The latter was shown in the present work for the first time. This paves a new way to reveal the relationships between the composition, structure, thermochemical response, and transport properties of complex oxides capable of reversible water uptake.

Perovskite-type oxides BaZr1–xYxO3−x/2 (x = 0.1, 0.2) were synthesized and their enthalpy increments were measured by means of high-temperature drop calorimetry in the temperature range of (373–1273) K in air. The data obtained were used for estimating the high-temperature thermodynamic functions (constant pressure heat capacity and entropy increments) of the zirconates BaZr1–xYxO3−x/2 (x = 0.1, 0.2). They were found to be only weakly dependent on the concentration of Y-dopant. Thermal expansion coefficient of zirconates BaZr1–xYxO3−x/2 (x = 0.1, 0.2) was successfully estimated by Grüneisen equation. Also, Neumann-Kopp rule was shown to be inapplicable for accurate estimation of heat capacities of the studied oxides. Thermodynamic analysis showed that BaZr1–xYxO3−x/2 (x = 0.1, 0.2) oxides are prone to chemical interaction with CO2 at typical working temperatures of proton-conducting solid oxide fuel cells. Some possibilities to overcome this issue have been discussed.

A comparatively simple method for estimating the mixing enthalpy of melts by differential scanning calorimetry using standard equipment is proposed. The enthalpies of mixing of CsX–PbX2 (X = Cl, Br) melts are determined by this method. The measured values of mixing enthalpy in the CsCl–PbCl2 system are in good agreement with those obtained by means of independent measurements. For the CsBr–PbBr2 system, the enthalpy of mixing was measured for the first time. The similar values of mixing enthalpy were found for both studied systems.

The differential scanning calorimetry study showed that the double perovskite HoBaCo2O6-δ (HBC), depending on its oxygen content, undergoes three phase transitions in the temperature range 298–773 K. Their origin was tentatively explained using the relevant literature data. For the single-phase tetragonal HBC, the oxygen nonstoichiometry dependences on the oxygen partial pressure were investigated by thermogravimetric and flow reactor methods in the intermediate-temperature range of 573–773 K. The proposed defect structure of HBC was successfully verified using the obtained data on its oxygen nonstoichiometry combined with those reported earlier. As a result, the values of the thermodynamic parameters (∆Hi∘, ∆Si∘) of the defect reactions proceeding in HBC were determined. The defect structure of HBC was shown to be similar to that of YBaCo2O6-δ (YBC) likely due to similar ionic radii of Ho3+ and Y3+.

Three different tetrachlorocuprates A2CuCl4 containing 3-aminopropionic, 4-aminobutyric and 6-aminohexanoic acid cations in A-sublattice were synthesized. The temperatures of the decomposition onset for A2CuCl4 were found to increase slightly with the aliphatic chain length in A cation. The standard reaction enthalpies for the formation from organic ammonium chloride and anhydrous copper (II) chloride at T = 298.15 K, Delta rH degrees hal,298 ("hal" denotes the formation from the source halides), were determined by isoperibolic solution calorimetry. The layer shift parameter S was introduced for the sake of comparison of thermochemical and structural data. Both original and literature thermochemical data indicate that simultaneous increase in S and decrease in the molar volume, Vmol, leads to a decrease in the Delta rH degrees hal,298.

Chemical compatibility and cation interdiffusion between the double perovskite cobaltites RBaCo2O6−δ (R = Gd, Pr) and proton-conducting electrolyte BaZr0.8Y0.2O3−δ were studied. Chemical interaction was found to occur already at 1100 °C as a result of the partial dissolution of RBaCo2O6−δ (R = Gd, Pr) in BaZr0.8Y0.2O3−δ. Analysis of the element distribution along the cross sections of diffusion couples RBaCo2O6−δ(R = Gd, Pr)|BaZr0.8Y0.2O3−δ showed strong interdiffusion of cations, with cobalt being the most mobile one. Its diffusion depth in the electrolyte reaches up to several hundreds of micrometers. The addition of NiO as a sintering aid to BaZr0.8Y0.2O3−δ promotes cation diffusion especially through the grain boundary mechanism, increasing the diffusion depth of Co. The possible implications of cation interdiffusion on the performance of proton-conducting SOFCs are discussed based on the results obtained.

Differential scanning calorimetry studies of the complex oxide YBaCo2O6-δ (YBC), combined with the literature data, allowed outlining the phase behavior of YBC depending on the oxygen content and temperature between 298 K and 773 K. The oxygen nonstoichiometry of single-phase tetragonal YBC was measured at different temperatures and oxygen partial pressures by both thermogravimetric and flow reactor methods. The defect structure of YBC was analyzed. As a result, the thermodynamic functions (∆Hi○, ∆Si○) of the defect reactions in YBC were determined. Experimental data on the oxygen content and those calculated based on the theoretical model were shown to be in good agreement. Standard enthalpies of formation at 298.15 K (∆Hf○) were obtained for YBC depending on its oxygen content using solution calorimetry. It was found that ∆Hf○ = f(6-δ) function is linear in the range of (6-δ) from 5.018 to 5.406 and that its slope is close to the value of the enthalpy of the quasichemical reaction describing oxygen exchange between the oxide and ambient atmosphere, which confirms the reliability of the suggested defect structure model.

Hybrid organic–inorganic perovskite halides, and, in particular, their mixed halide solid solutions, belong to a broad class of materials which appear promising for a wide range of potential applications in various optoelectronic devices. However, these materials are notorious for their stability issues, including their sensitivity to atmospheric oxygen and moisture as well as phase separation under illumination. The thermodynamic properties, such as enthalpy, entropy, and Gibbs free energy of mixing, of perovskite halide solid solutions are strongly required to shed some light on their stability. Herein, we report the results of an experimental thermochemical study of the CH3NH3Pb(Cl1−xBrx)3 mixed halides by solution calorimetry. Combining these results with molecular dynamics simulation revealed the complex and irregular shape of the compositional dependence of the mixing enthalpy to be the result of a complex interplay between the local lattice strain, hydrogen bonds, and energetics of these solid solutions.

This article reviews the state of the art – from the experimental and computational data available to the models, origins and possible uses – in the field of chemical strain of oxide materials (primarily those for elevated-temperature applications).

Standard formation enthalpies of some solid piperazine salts: C4H12N2(NO3)2, C4H12N2Cl2 and C4H12N2Cl2·H2O at 298.15 K were measured using combustion and solution calorimetry. The following values were obtained: ΔfH298°(C4H12N2(NO3)2) = (-594.4 ± 2.7) kJ·mol−1, ΔfH298°(C4H12N2Cl2) = (-475.6 ± 2.9) kJ·mol−1, ΔfH298°(C4H12N2Cl2·H2O) = (-772.3 ± 2.9) kJ·mol−1 (expanded uncertainties, 95% confidence level). The hydration enthalpies of piperazinium dichloride by gaseous and liquid water were found to be equal to (-54.82 ± 0.09) kJ·mol−1(H2O) and (-10.83 ± 0.09) kJ·mol−1(H2O), respectively (expanded uncertainties, 95% confidence level). The results obtained allowed estimating ΔfH298° of aqueous C4H12N22+ ions as (-128.5 ± 2.9) kJ·mol−1 (expanded uncertainty, 95% confidence level), which is in good agreement with the value of (-129.0 ± 3.3) kJ·mol−1 (expanded uncertainty, 95% confidence level) that was calculated using the literature data.

The results of thermochemical study of the CsPbCl3 formation thermodynamics available in literature were critically evaluated by comparison with those calculated from the temperature dependence of EMF of galvanic cells involving CsPbCl3 as well as with the newly obtained solution calorimetric data. The origin of the discrepancy between the values of standard formation enthalpy reported by different scientific groups was identified. Redetermined solution enthalpy of CsPbCl3 in dimethyl sulfoxide allowed correcting the earlier reported value of the standard formation enthalpy of CsPbCl3. As a result, the following consistent set of the thermodynamic functions for CsPbCl3 was obtained: $${\Delta }_{\mathrm{f}}{H}_{298}^{^\circ }$$  = (–810.3 ± 0.4) kJ mol−1, $${S}_{298}^{^\circ }$$  = (270.1 ± 4.3) J mol−1 K−1.

Mixed conducting cobaltites PrBaCo2−xFexO6−δ (x = 0–0.6) with a double perovskite structure are promising materials for ceramic semi-permeable membranes for oxygen separation and purification due to their fast oxygen exchange and diffusion capability. Here, we report the results of the detailed study of an interplay between the defect chemistry, oxygen nonstoichiometry and oxygen transport in these materials as a function of iron doping. We show that doping leads to a systematic variation of both the thermodynamics of defect formation reactions and oxygen transport properties. Thus, iron doping can be used to optimize the performance of mixed conducting oxygen-permeable double perovskite membrane materials.

The defect structure model of La0.5Ba0.5CoO3–δ was successfully verified using a combined set of coulometric and thermogravimetric data. The results were used to model the dependences of Seebeck coefficient, measured vs T and pO2 simultaneously with the total conductivity, and chemical strain of this oxide. The partial molar enthalpy of oxygen in La0.5Ba0.5CoO3–δ was calculated from the defect structure model and used to evaluate the enthalpy increments and high-temperature heat capacity of an oxide with constant chemical composition, La0.5Ba0.5CoO2.99, from the drop calorimetric measurement results in air. The standard enthalpies of formation of cubic La0.5Ba0.5CoO2.95 and double LaBaCo2O5.90 perovskites, and the enthalpy of cation ordering in A-sublattice of La0.5Ba0.5CoO2.95, were found using the results of solution calorimetry at 298.15 K. With the data obtained, we predicted the chemical compatibility of La0.5Ba0.5CoO3–δ with solid oxide fuel cell (SOFC) electrolyte materials.