Electrochemical determination of SrFe12O19 impurity in perovskite ferrites

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-delta (x = 0, 0.1, 0.2), the latter two compositions of which have been found to be contaminated with similar to 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-delta. 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. (c) 2021 Elsevier B.V. All rights reserved.