Observation of Cu-rich grain boundary nanoparticles and complexions in Cu/Ti-doped alumina

Abstract Alumina powders were processed with 7.8 wt% CuO and post-sintering reduction heat-treatments were applied with the aim of producing metallic grain boundary complexions. The influence of titanium co-doping was also studied. Grain boundaries were characterized by aberration-corrected scanning transmission electron microscopy. Copper grain boundary enrichment was achieved, but only in the titanium doped samples; the segregated copper exhibited a Cu 2+ valency state, the segregated titanium exhibited Ti 3+ or Ti 4+ valency states, and metallic Cu nanoparticles were also observed. The crystallographic orientation of the grain boundary plane had a marked influence on concentration and oxidation state of the segregating species.