Cation ${(}^{63}$Ni) diffusion in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial films

The diffusion of ${}_{}{}^{63}{}_{}{}^{}\mathrm{Ni}$ has been measured in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ epitaxial thin films on (100) ${\mathrm{SrTiO}}_3$ substrates in the 550–650 °C range (orthorhombic phase) in ${\mathrm{O}}_2$ pressure of 1 bar, keeping δ in the 0.3–0.4 range. The diffusion behavior is described by D=1.3 exp[(-2.7 eV)/kT] ${\mathrm{cm}}^2$/sec and is many orders of magnitude slower than anion (oxygen) diffusion reported in the literature. A diffusion mechanism involving thermal vacancies and atomic jumps in diagonal directions of the type 〈110〉, 〈301〉, and 〈031〉 is proposed for long-range diffusion of cations occupying the Cu sites.