Evidence of ion diffusion at room temperature in microcrystals of the Bi2Sr2CaCu2O8+delta superconductor

TL;DR

This study provides evidence of ion diffusion, specifically oxygen out-diffusion and copper cation migration, occurring at room temperature in Bi2Sr2CaCu2O8+delta microcrystals over 40 days, revealing dynamic compositional changes.

Contribution

It demonstrates room-temperature ion diffusion in Bi-2212 microcrystals, combining advanced spectroscopic techniques with electrical measurements to reveal cation and oxygen migration.

Findings

Cu+ increases relative to Cu2+ near edges

Enrichment of Cu compared to Bi and Sr at edges

Oxygen loss detected by resistivity and thickness changes

Abstract

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 Cu$^{2+}$ 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 out-diffusion along the b-axis is accompanied by Cu cation migration in the same direction.