Preparation and characterization of YBaCo4–yCuyO7 + x compounds

Abstract

Phase formation processes along the YBa(Co, Cu)₄O_{7 + x} section of the Y–Ba–Co–Cu–O system have been studied in the temperature range 900–1150°C under atmospheric oxygen pressure. We have located the boundaries of the homogeneity range of the YBaCo_4–yCu_yO_{7 + x} (114) phase and determined the temperature- dependent copper solubility in this phase, y_max(t) (y_max ≈ 0 at 900°C; the highest solubility is y_max ≈ 0.7, at t = 1000–1050°C). Using X-ray diffraction data for quenched samples, we have identified the phases that coexist with YBaCo_4–yCu_yO_{7 + x} in the phase regions adjacent to its homogeneity range. The results demonstrate that, if the percentage of copper in a starting mixture, y₀, exceeds the copper solubility limit in the 114 phase at a given synthesis temperature, the excess copper concentrates in copper-rich phases: YBaCo_2–yCu_yO_{5 + x} (112), Co_1–yCu_yO_{1 + x} (001), and Y₂Cu₂O_{5 + x} (202). At temperatures in the range 900 ≤ t ≤ 1050°C and compositions in the range y₀ ≤ 0.9, the system can be thought of as ternary, with a constant Y: Ba ratio of 1: 1 (that is, only the 114, 112, and 001 phases are present at equilibrium). Beyond this region, phases with other Y: Ba ratios appear.