PHASE RELATION IN THE Fe2O3-Gd2O3 SYSTEM AT 1300 AND 1400 °С

Abstract

The phase interaction in the Fe₂O₃–Gd₂O₃ system at 1300 and 1400 °C were studied across the full concentration range using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Samples, prepared in 1–5 mol% composition increments, were obtained by dissolving the oxides in HNO₃ (1 : 1), evaporating the solutions, and decomposing the nitrates at 800 °C for 2 h. The resulting powders were pressed at 10 MPa into 5 mm × 4 mm pellets and heat-treated in air at 1300 °C (300 h) and 1400 °C (100 h). The phase composition was determined using X-ray diffraction (XRD, DRON-3) and microstructural analysis (Superprobe-733, JEOL, Japan; Palo Alto, California, USA). At 1300 and 1400 °C, the isothermal sections of the Fe₂O₃–Gd₂O₃ phase diagram comprise four single-phase regions (B–Gd₂O₃, GdFeO₃(R), Gd₃Fe₅O₁₂, Fe₂O₃) and three two-phase regions (B–Gd₂O₃ + GdFeO₃, GdFeO₃ + Gd₃Fe₅O₁₂, Gd₃Fe₅O₁₂ + Fe₂O₃). The concentration dependence of the unit cell parameters for phases in the studied system was established. In the Fe₂O₃–Gd₂O₃ system at 1300 and 1400 °C, an ordered perovskite-type phase with orthorhombic distortion (GdFeO₃) is formed. Its homogeneity range at both temperatures extends from 48 to 52 mol.% Gd₂O₃.