Evidence of ion diffusion at room temperature in micro-sized crystals of the Bi2Sr2CaCu2O8+d superconductor

We have studied Bi-2212 microcrystals aged at ambient conditions for 40 days. Combined x-ray absorption near edge structure and x-ray fluorescence measurements with micrometer space resolution show both an increase of Cu+ with respect to Cu2+ and an enrichment in Cu vs Bi and Sr cation content near the sample edges in the b-axis direction. A parallel study on an electrically contacted sample has indirectly detected the O loss, observing both a resistivity increase and an increase in sample thickness near the edges. We conclude that the O outdiffusion along the b axis is accompanied by Cu cation migration in the same direction.