Site selectivity and cation diffusion in YBa2Cu3O7- delta.

Abstract

Tracer diffusion of Co, Zn, and Cu has been studied in polycrystals of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ from 600 to 950 \ifmmode^\circ\else\textdegree\fi{}C at an oxygen partial pressure of 1 atm using serial sectioning or the secondary-ion mass spectrometry technique. The present and previously published values of the diffusion coefficient of Cu fall on the same Arrhenius line. The diffusion coefficients of Zn and Cu and published values for Ni are close to each other and the activation energies are almost the same. Measurements of diffusion of Co and Ni in single-crystal c-axis platelets indicate a much greater diffusional anisotropy for Co than for Ni. Diffusion coefficients of Cu are less than published diffusion coefficients of Ag, possibly because Ag attracts oxygen-ion vacancies. The interaction between cations and oxygen vacancies can explain the increase in the diffusion of Cu with decreasing ${\mathit{P}}_{\mathrm{O}2}$ at 850 \ifmmode^\circ\else\textdegree\fi{}C.