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

The phase equilibria in the Y–Ba–Co–O system were systematically studied at 1373K in air. The intermediate phases formed in the Y–Ba–Co–O system at 1373K 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 298K up to 1073K under Po2=0.21аtm 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 1323K 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 298–1273K. 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 298–1373K in air. Thermal expansion of BaCo1−yYyO3−δ (у=0.0; 0.1; 0.2; 0.3) samples was studied within the temperature range 298–1200K 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. A projection of isobaric isothermal phase diagram of the Y–Ba–Co–O system to the metallic components triangle (T=1373K, Po2=0.21atm). [Display omitted] •High-temperature X-ray diffraction analyses of the YBaCo2O5+δ in the temperature range 298–1073K.•The value of oxygen content for the YBaCo2O5+δ in the temperature range 298 –1323K.•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.