Oxygen analysis for high- Tc copper oxides: an alternative method for the determination of solid solution limits

Abstract

The variation of oxygen content with cation substitution for several types of high- T c copper oxide solid solutions has been analyzed in terms of both theoretical derivations and experiments. It has been found that for continuous solid solutions the oxygen content varies with substitution in a linear manner over the entire substitution region, while for discontinuous solid solutions the first derivatives of the oxygen content with respect to substitution is discontinuous at the solid solution limit. For the latter, the oxygen content varies in the same way as continuous solid solutions with substitution within the solution limits. However, beyond the solid solution limits, oxygen contents vary with substitution either in a linear manner but with different slope or in a curvy manner, depending on the properties of the component elements of the solid solutions. Therefore, we can determine the solid solution limit or, rather, detect the existence of minor amounts of impurities from the plot of the variation of oxygen content with substitution. The determination of the oxygen content by iodometric titration have verified the above conclusions. The solid solution limits determined by our method are in good agreement with those by powder X-ray diffraction. In some cases, the present method has advantages over conventional powder X-ray diffraction for determining the solid solution limits.