The local laser heating of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3^{18}$${\mathrm{O}}_{6.2}$ in air was used to study the oxygen diffusion and oxygen ordering in sample volumes of the order of a few μ${\mathrm{m}}^3$. Raman microprobe at points corresponding to different annealing temperatures was applied to monitor both the stages of substitution of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ for ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ at different oxygen sites and the structural changes in the basal [Cu(1)-O(1)] planes occurring during the oxygen in-diffusion. The population of the O(1) sites initially results in the formation of short Cu(1)-O(1) fragments which later conjunct into long chains. The results can be applied for a better understanding of oxygen reordering processes in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ during thermal treatment.

• Received 11 July 1995

DOI:https://doi.org/10.1103/PhysRevB.52.13652