Tracer diffusion of oxygen in ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_{\mathit{x}}$

Tracer diffusion of ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ has been investigated in dense polycrystals and in the c direction in single crystals of ${\mathrm{Bi}}_2$ ${\mathrm{Sr}}_2$ ${\mathrm{CaCu}}_2$ ${\mathrm{O}}_{\mathit{x}}$ between 300 and 700 °C under one atmosphere of oxygen. Penetration profiles were determined by secondary-ion mass spectrometry. The diffusional anisotropy as measured by the ratio of the diffusion coefficients in the polycrystals [D=1.7×${10}^{\mathrm{-}5}$ exp(-0.93 eV/kT) ${\mathrm{cm}}^2$/s] to the diffusion coefficients parallel to the c axis of the single crystals [D=0.6 exp(-2.20 eV/kT) ${\mathrm{cm}}^2$/s] is large and temperature dependent. The results suggest that diffusion in the ab plane and in the c direction takes place by different mechanisms.