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 Nd2O3 – SrO – ½ Fe2O3 system were systematically studied at 1373K in air. The homogeneity ranges and crystal structure of the solid solutions Nd1-xSrxFeO3-δ with 0.0≤x≤0.6 (sp. gr. Pbnm) and with 0.7≤x≤0.9 (sp. gr. Pm3m), Sr2-yNdyFeO4-δ with 0.7≤y≤0.9 (sp. gr. I4/mmm), Sr3-zNdzFe2O7-δ with 0.0≤z≤0.4 and 1.8≤z≤1.9 (sp. gr. I4/mmm) and Sr4-uNduFe3O10-δ with 0.7≤u≤0.9 (sp. gr. I4/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 Nd1-xSrxFeO3-δ (0.2≤x≤0.9), Sr3-zNdzFe2O7-δ (0.0≤z≤0.4 and z=1.9) and Sr4-uNduFe3O10-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 Nd1-xSrxFeO3-δ (0.6≤x≤0.8) samples were calculated within the temperature range 298–1373K 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.