Possible origin of high proton/deuteron solubility at 10GDC grain boundaries

Abstract

To understand the proton dissolution behavior into 10GDC from water vapor, a deuteron map of polycrystalline 10GDC was collected using nanoscale secondary ion mass spectrometry (NanoSIMS) as an indicator of proton distribution. NanoSIMS imaging clearly revealed that deuterons dissolved mainly into grain boundaries. Because Gd enrichment was observed at grain boundaries, the effect of Gd concentration (10–40 mol%) on deuteron solubility was also investigated using dynamic SIMS. For 10GDC, the bulk deuteron solubility was very low (4.8 × 1017 cm−3) compared to grain boundaries, while the bulk solubility significantly increased with increasing Gd concentration (1.1 × 1019 cm−3 for 30GDC). This indicates that Gd enrichment is at least partly responsible for the high proton/deuteron solubility at grain boundaries. The bulk solubility increase upon high-concentration Gd doping can be attributed to the lower electronegativity of Gd3+ compared to Ce4+, which results in increased oxygen basicity.