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The applicability of perovskite-type SrVO3-δ in high-temperature electrochemical energy conversion technology is hampered by the limited stability domain of the perovskite phase. The aim of the present work was to find a compromise between the phase stability and electrical performance by designing solid solutions in the SrVO3 -SrTiO3 system. Increasing titanium content in SrV1-y Tiy O3-δ (y=0-0.9) perovskites is demonstrated to result in a gradual shift of the upper-p(O2 ) phase stability boundary toward oxidizing conditions: from ≈10-15 bar at 900 °C for undoped SrVO3-δ to ≈10-11 -10-5 bar for y=0.3-0.5. Although the improvement in the phase stability is accompanied by a decrease in electrical conductivity, the conductivities of SrV0.7 Ti0.3 O3-δ and SrV0.5 Ti0.5 O3-δ at 900 °C remain as high as 80 and 20 S cm-1 , respectively, and is essentially independent of p(O2 ) within the phase-stability domain. Combined XRD, thermogravimetric analysis, and electrical studies revealed very sluggish kinetics of oxidation of SrV0.5 Ti0.5 O3-δ ceramics under inert gas conditions and a nearly reversible behavior after exposure to an inert atmosphere at elevated temperatures. Substitution by titanium in the SrV1-y Tiy O3-δ system results also in a decrease of oxygen deficiency in perovskite lattice and a favorable suppression of thermochemical expansion. Variations of oxygen nonstoichiometry and electrical properties in the SrV1-y Tiy O3-δ series are discussed in combination with the simulated defect chemistry of solid solutions.

Perovskite-related (La1-xSrx)(2)NiO4-delta (x= 0.5-0.8) phases were explored for possible use as oxygen electrodes in solid electrolyte cells with a main focus on the effect of oxygen deficiency on ...

Phase formation under high pressure in the chalcopyrite–delafossite system has been studied at 5 GPa and 500–1000 °C. The parent chalcopyrite composition used in this study was slightly Cu-deficient, corresponding to the chemical formula (Cu,Ga)0.905GaS2. It was revealed that under high-pressure and high-temperature conditions, a mixture of the parent phases partly decomposes to form Cu2S and Ga2O3. The defect chalcopyrite (Cu,Ga)0.905GaS2 splits into a near-stoichiometric CuGaS2 and a Cu-deficient cubic (sphalerite-like) phase of the (Cu,Ga)0.8S composition. Such a phenomenon has been considered in terms of characteristic features of chalcopyrite and sphalerite crystal structures. Delafossite CuGaO2 at 5 GPa and 1000 °C was found to recrystallize entirely, which results in the disappearance of the stacking faults in its layered structure.

Cation-stoichiometric and strontium-deficient Sr1−xCexTiO3 ± δ (0

This work presents the processing and the characterization of diopside–Ca-Tschermak clinopyroxene-based glass–ceramics (GCs), where partial (i.e., 5%, 10%, and 20%) substitution of Ba for Ca was attempted in the composition of CaMg0.8Al0.4Si1.8O6. Sintering, crystallization, microstructure, and properties of the new materials were investigated under different heat-treatment conditions concerning heating rates (5–40 K/min), temperatures (850°–1000°C), and times (1–300 h). The good matching of thermal expansion coefficients and the strong, but not reactive, adhesion to yttria-stabilized cubic zirconia, in conjunction with the low level of electrical conductivity and oxygen permeability, indicate that the investigated GCs are suitable for further experimentation as candidates for solid oxide fuel cells sealants.

This paper is focused on the comparative analysis of data on electronic and ionic conduction in gadolinia-doped ceria (CGO) ceramics as well as on the electrochemical properties of various oxide electrodes in contact with ceria-based solid electrolytes. Properties of electrode materials, having thermal expansion compatible with that of doped ceria, are briefly reviewed. At temperatures below 1000 K, Ce0.90Gd0.10O2−δ (CGO10) was found to possess a better stability at reduced oxygen pressures than Ce0.80Gd0.20O2−δ (CGO20). Incorporation of small amounts of praseodymium oxide into Ce0.80Gd0.20O2−δ leads to a slight improvement of the stability of CGO20 at intermediate temperatures, but the difference between electrolytic domain boundaries of the Pr-doped material and CGO10 is insignificant. Since interaction of ceria-based ceramis with electrode materials, such as lanthanum-strontium manganites, may result in the formation of low-conductive layers at the electrode/electrolyte interface, optimization of electrode fabrication conditions is needed. A good electrochemical activity in contact with CGO20 electrolyte was pointed out for electrodes of perovskite-type La0.8Sr0.2Fe0.8Co0.2O3−δ and LaFe0.5Ni0.5O3−δ, and LaCoO3−δ/La2Zr2O7 composites; surface modification of the electrode layers with praseodymium oxide results in considerable decrease of cathodic overpotentials. Using highly-dispersed ceria for the activation of SOFC anodes significantly improves the fuel cell performance.

Ba4Nb2O9 is shown to have two basic polymorphs: a high-temperature γ phase, which represents an entirely new structure type; and a low-temperature α phase, which has the rare Sr4Ru2O9 structure type. The phases are separated by a reconstructive phase transition at ∼1370 K, the kinetics of which are sufficiently slow that the γ phase can easily be quenched to room temperature. Below ∼950 K, both α and γ phases absorb significant amounts of water. In the case of the γ phase, protons from absorbed water occupy ordered positions in the structure, giving rise to a stoichiometric phase γ-III-Ba4Nb2O9·1/3H2O at room temperature. γ-III-Ba4Nb2O9·1/3H2O partially dehydrates at ∼760 K to give another stoichiometric phase γ-II-Ba4Nb2O9·1/6H2O, which completely dehydrates at ∼950 K to γ-I-Ba4Nb2O9. The hydrated γ phases exhibit faster protonic and oxide ionic transport than the hydrated α phases because of the presence in the gamma phases of 2D layers containing Nb5+ cations with unusually low oxygen coordination numb...