Resistance measurements and oxygen out-diffusion near the orthorhombic-tetragonal phase transformation in single-crystal YBa2Cu3O7- delta.

Abstract

Isothermal resistance measurements and hot-stage optical microscopy were used to simultaneously follow the loss of oxygen and the disappearance of the twin structure in single-crystal ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ from 590--720\ifmmode^\circ\else\textdegree\fi{}C. Oxygen out-diffusion was found to follow surface-reaction-limited conditions with an activation energy of 1.2\ifmmode\pm\else\textpm\fi{}0.1 eV. Although the crystal was driven through the orthorhombic-tetragonal phase transformation during the isothermal anneals, no anomalous resistance behavior was observed. This suggests that previous observations of anomalous resistance behavior in bulk ceramics may not be intrinsic to ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$. The difference between oxygen in-diffusion and out-diffusion kinetics is discussed in relation to the twin structure observed near the orthorhombic-tetragonal phase transformation.