Phase equilibria, crystal structure and oxygen content of intermediate phases in the Y–Ba–Co–O system

•High-temperature X-ray diffraction analyses of the YBaCo2O5+δ in the temperature range 298–1073 K.•The value of oxygen content for the YBaCo2O5+δ in the temperature range 298 –1323 K.•The homogeneity range and crystal structure of the BaCo1−yYyO3−δ (0.09≤y≤0.42) solid solutions.•Oxygen nonstoichiometry of BaCo1−yYyO3−δ solid solutions.•The projection of isothermal–isobaric phase diagram for the Y–Ba–Co–O system.

The phase equilibria in the Y–Ba–Co–O system were systematically studied at 1373 K in air. The intermediate phases formed in the Y–Ba–Co–O system at 1373 K in air were: YBaCo2O5+δ, YBaCo4O7 and BaCo1−yYyO3−δ (0.09≤y≤0.42). It was shown that YBaCo2O5+δ possesses tetragonal structure with the 3ap×3ap×2ap superstructure (sp. gr. P4/mmm). High-temperature X-ray diffraction analysis of the YBaCo2O5+δ in the temperature range from 298 K up to 1073 K under Po2=0.21 аtm has not shown any phase transformations. The value of oxygen content for the YBaCo2O5+δ at room temperature was estimated as 5.40 and at 1323 K it was equal to 5.04. Thermal expansion of sample shows a linear characteristics and the average thermal expansion coefficient (TEC) is about 13.8×10−6, K−1 in the temperature range 298–1273 K. The homogeneity range and crystal structure of the BaCo1−yYyO3−δ (0.09≤y≤0.42) solid solutions were determined by X-ray diffraction of quenched samples. All BaCo1−yYyO3−δ solid solutions were found to have cubic structure (sp. gr. Pm3m). The unit cell parameters were refined using Rietveld full-profile analysis. Oxygen nonstoichiometry of BaCo1−yYyO3−δ solid solutions with 0.1≤y≤0.4 was measured by means of thermogravimetric technique within the temperature range 298–1373 K in air. Thermal expansion of BaCo1−yYyO3−δ (у=0.0; 0.1; 0.2; 0.3) samples was studied within the temperature range 298–1200 K in air. The projection of isothermal–isobaric phase diagram for the Y–Ba–Co–O system to the compositional triangle of metallic components was presented.

Graphical abstractA projection of isobaric isothermal phase diagram of the Y–Ba–Co–O system to the metallic components triangle (T=1373 K, Po2=0.21 atm). Figure optionsDownload full-size imageDownload as PowerPoint slide