Phase equilibria in the Nd 2 O 3 –BaO–Fe 2 O 3 system: Crystal structure, oxygen content, and properties of intermediate oxides

Abstract The phase equilibria in the ½Nd 2 O 3 –BaO–½Fe 2 O 3 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: Nd 1‐ x Ba x FeO 3‐ δ with 0.0 ≤ x ≤ 0.05 (space group (SG) Pnma ) and with 0.6 ≤ x ≤ 0.7 (SG Pm ‐3 m ), Ba 6+ y Nd 2‐ y Fe 4 O 15‐ δ with 0.0 ≤ y ≤ 0.4 (SG P 6 3 mc ), and Ba 1.1 Nd 1.9 Fe 2 O 7‐ δ (SG P 4 2 / mnm ). The structural parameters of single‐phase oxides were refined by the Rietveld method. The changes in oxygen content for Nd 1‐ x Ba x FeO 3‐ δ (0.6 ≤ x ≤ 0.7), Ba 6 Nd 2 Fe 4 O 15‐ δ , and Ba 1.1 Nd 1.9 Fe 2 O 7‐ δ versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by barium in the Nd 1‐ x Ba x FeO 3‐ δ (0.6 ≤ x ≤ 0.7) oxides leads to a decrease of oxygen content. Partial ordering via formation of separate domains with a p × a p × 5 a p superstructure in Nd 0.4 Ba 0.6 FeO 3‐ δ , which cannot be detected by XRD, noticeably influence its thermal expansion and electrical conductivity.