The structure, nonstoichiometry, and thermodynamic characteristics of oxygen in strontium ferrite doped with niobium, SrFe1 − x Nb x O3 − δ

Abstract

The influence of doping with niobium on the structure and oxygen nonstoichiometry of strontium ferrite SrFe1 − x Nb x O3 − δ (x = 0.05, 0.1, 0.2, 0.3, and 0.4) was studied. The content of oxygen in the doped derivatives was determined by coulometric titration as a function of temperature (650–950°C) and oxygen partial pressure in the gas phase (10−4−1 atm). The partial molar enthalpies Δ\( \bar H_O \)(x, δ) and entropies Δ\( \bar S_O \)(x, δ) of oxygen in SrFe1 − x Nb x O3 − δ were calculated. An analysis of Δ\( \bar S_O \)(x, δ) dependences showed that the model of a random distribution of ions and vacancies over accessible sites in the oxygen sublattice allowed the experimental data to be described satisfactorily. An increase in the partial enthalpy Δ\( \bar H_O \)(x, δ) as nonstoichiometry δ decreased was indicative of weak repulsive interactions between oxygen ions in the structure of SrFe1 − x Nb x O3 − δ.