Oxygen nonstoichiometry in high-Tc superconductor HoBa2Cu3O6+x and application of coulometric tritration

Nonstoichiometry in the perovskite-type compound, HoBa₂Cu₃O_6+x, was determined as a function of oxygen partial pressure (5 × 10^?1 1 × 10⁵ Pa) in the temperature range of 8631173 K by coulometric titration using a stabilized zirconia electrolyte. Electromotive force of the cell, EMF, was measured as a function of oxygen content at constant temperature, and as a function of temperature at constant oxygen content. The perovskite-type compound was found to have a tendency to decompose into Ho₂O₃, BaO, CuO and some double-oxides at low oxygen partial pressures. Defect equilibria are discussed on the basis of the dependence of nonstoichiometry on oxygen partial pressure. Variation of the relative partial molar entropy with composition is explained in terms of a well-known defect model. A new technique which was developed for measuring the electrical conductivity of a non-stoichiometric oxide, in situ, at constant oxygen content as a function of temperature in the coulometric titration cell, is presented.