Electrochemical determination of SrFe12O19 impurity in perovskite ferrites

Abstract

A strong negative effect of SrFe12O19 impurity presence in perovskite-type ferrites on the results of the coulometric titration has been revealed. A multistage decomposition of this impurity during reductive titration causes distortion of oxygen content isotherms and makes the obtained data inapplicable for the defect equilibrium analysis. Even a small amount of SrFe12O19 undetected by X-ray diffraction has been shown to affect data considerably. In this study, a method has been developed to determine the amount of impurity and recover the oxygen content data in perovskite-type ferrites from measurements of these ferrites contaminated with SrFe12O19. The method has been verified on the perovskite-type NdxSr1−xFe0.8Mo0.2O3−δ (x = 0, 0.1, 0.2), the latter two compositions of which have been found to be contaminated with ~0.9 and 1.8 wt% of SrFe12O19, respectively, whereas 5.8 wt% of hexaferrite has been intentionally admixed to the x = 0 composition. The recovered data have been used for thermodynamic modeling of the defect equilibrium in NdxSr1−xFe0.8Mo0.2O3−δ. Good agreement of all obtained thermodynamic parameters with the published results for similar compositions and their monotonous change with neodymium content confirms the correct functionality of the method.