Phase equilibria in the Nd2O3–BaO–Fe2O3 system: Crystal structure, oxygen content, and properties of intermediate oxides

Abstract

AbstractThe phase equilibria in the ½Nd2O3–BaO–½Fe2O3 system were systematically studied at 1373 K in air and presented in the form of a phase diagram. By X‐ray diffraction (XRD) analysis of quenched samples, the homogeneity ranges and crystal structure were determined for the following intermediate oxides: Nd1‐xBaxFeO3‐δ with 0.0 ≤ x ≤ 0.05 (space group (SG) Pnma) and with 0.6 ≤ x ≤ 0.7 (SG Pm‐3m), Ba6+yNd2‐yFe4O15‐δ with 0.0 ≤ y ≤ 0.4 (SG P63mc), and Ba1.1Nd1.9Fe2O7‐δ (SG P42/mnm). The structural parameters of single‐phase oxides were refined by the Rietveld method. The changes in oxygen content for Nd1‐xBaxFeO3‐δ (0.6 ≤ x ≤ 0.7), Ba6Nd2Fe4O15‐δ, and Ba1.1Nd1.9Fe2O7‐δ versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by barium in the Nd1‐xBaxFeO3‐δ (0.6 ≤ x ≤ 0.7) oxides leads to a decrease of oxygen content. Partial ordering via formation of separate domains with ap × ap × 5ap superstructure in Nd0.4Ba0.6FeO3‐δ, which cannot be detected by XRD, noticeably influence its thermal expansion and electrical conductivity.