Oxygen nonstoichiometry and high-temperature conductivity of DyBa 2Cu 3O 7−δ

Abstract

The oxygen nonstoichiometry and high-temperature conductivity of DyBa 2Cu 3O 7−δ were measured as functions of temperature and oxygen partial pressure P(O 2). When the δ-log P(O 2) data points at each temperature are shifted in parallel in the abscissa direction by a distance characteristic of temperature, a single smooth curve called “the master curve” was formed. A proposed model, based on chemical equilibria among electronic defects, ionic defects and oxygen well, interpreted “the master curve”. The high-temperature conductivity was plotted against the excess copper valence Δz( z - 1.67) calculated from the oxygen nonstoichiometry. All the data points were found to fall on a single curve, irrespective of temperature. Assuming that Cu Cu ions are the charge carrier, the mobility was calculated from the conductivity. The lattice parameters as a function of Δ have suggested that the increase in mobility with increasing average copper valence could be due to the concentration change of oxygen on the Cu(1)-O plane.