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.

A 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 as PowerPoint slide