Crystal structure and thermal and electrical properties of the perovskite solid solution Nd_1−xSr_xFeO_3−δ (0≤x≤0.4)

Abstract

The crystal structure, thermal expansion and electrical conductivity of strontium-doped neodymium ferrite (Nd_1−xSr_xFeO_3−δ, where 0≤x≤0.4) were investigated. All compositions had the GdFeO_3-type orthorhombic perovskite structure. The lattice parameters were determined at room temperature by X-ray powder diffraction. The orthorhombic distortion decreases with increasing Sr substitution. The pseudocubic lattice parameter shows a minimum at x=0.3. The thermal expansion curves for x=0.2–0.4 displayed rapid increase in slope at higher temperatures. The electrical conductivity increased with Sr content and temperature. The calculated activation energies for electrical conduction decreased with increasing x. The electrical conductivity can be described by the small polaron hopping mechanism. The charge compensation for divalent ion on the A-site is provided by the formation of Fe⁴⁺ ions on the B site and vacancies on the oxygen sublattice. The results indicate two defect domains: for low values of x, the predominant defect is Fe⁴⁺ ions, whereas for higher values of x, oxygen vacancies dominate.