Phase equilibria, crystal structure, oxygen nonstoichiometry and thermal expansion of complex oxides in the Nd2O3 – SrO – Fe2O3 system

Abstract The phase equilibria in the ½ Nd 2 O 3 – SrO – ½ Fe 2 O 3 system were systematically studied at 1373 K in air. The homogeneity ranges and crystal structure of the solid solutions Nd 1- x Sr x FeO 3-δ with 0.0≤ x ≤0.6 (sp. gr. Pbnm ) and with 0.7≤ x ≤0.9 (sp. gr. Pm 3 m ), Sr 2- y Nd y FeO 4-δ with 0.7≤ y ≤0.9 (sp. gr. I 4 /mmm ), Sr 3- z Nd z Fe 2 O 7-δ with 0.0≤ z ≤0.4 and 1.8≤ z ≤1.9 (sp. gr. I 4 /mmm ) and Sr 4- u Nd u Fe 3 O 10-δ with 0.7≤ u ≤0.9 (sp. gr. I 4 /mmm ) were determined by X-ray diffraction analysis of quenched samples. The structural parameters of single-phase oxides were refined by the Rietveld profile method. The changes of oxygen content in the solid solutions Nd 1- x Sr x FeO 3-δ (0.2≤ x ≤0.9), Sr 3- z Nd z Fe 2 O 7-δ (0.0≤ z ≤0.4 and z =1.9) and Sr 4- u Nd u Fe 3 O 10-δ (0.7≤ u ≤0.9) versus temperature in air were determined by thermogravimetric analysis. Gradual substitution of neodymium by strontium leads to the decrease of the oxygen content. The average thermal expansion coefficients for the Nd 1- x Sr x FeO 3-δ (0.6≤ x ≤0.8) samples were calculated within the temperature range 298–1373 K in air. The project of isothermal-isobaric phase diagram for the Nd-Sr-Fe-O system to the compositional triangle of metallic components was presented.