Crystal structure, oxygen nonstoichiometry, thermal expansion and conductivity of (Nd,Sr)(Fe,Co)O3 - δ oxides

A series of samples with overall composition Nd-1 - xSrxFe1 - yCOyO3 (- delta) (x = 0.7, 0.0 <= y <= 1.0) and (y = 0.3, 0.0 <= x <= 1.0) were prepared by glycerol nitrate technique and characterized by X-ray diffraction, thermogravimetric analysis, iodometric titration and dilatometry. Nd-1 (-) xSrxFe0.7CO0.3O3 (-) (delta) with 0.0 <= x <= 0.5 possesses orthorhombic structure (sp. gr. Pbnm) and reveals O-type -> O'-type -> O-type structural transition around x = 0.3. The orthorhombic distortion decreases with the increasing strontium substitution and solid solutions Nd-1 - xSrxFe0.7Co0.3O3 (- delta) with 0.7 <= x <= 1.0 and Nd0.3Sr0.7Fe1 - yCoyO3 - (delta) with 0.0 <= y <= 1.0 exhibit the cubic structure (sp. gr. Pm3m). The structural parameters were refined using Rietveld full-profile analysis. The changes of oxygen content in Nd-1 - xSrxFe1 - yCoyO3 (-) (delta) versus temperature were determined by the thermogravimetric analysis. The gradual substitution of neodymium by strontium or of iron by cobalt leads to the decrease of oxygen content. The thermal expansion measurements of Nd1 - xSrxFe0.7Co0.3O3 - (delta) (x = 0.3; 0.4; 0.5 and 0.7) were performed and chemical expansion constituents have been separated. The electrical conductivity significantly increased with strontium content in low temperature range. The influence of Sr content diminished in high temperature range. (C) 2016 Elsevier B.V. All rights reserved.