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

Abstract

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 atm 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 (y=0.0; 0.1; 0.2; 0.3) samplesmore » 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 abstract: 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). Highlights: • 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+δin 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.« less