Grain boundary microstructures in a liquid-phase sintered alumina (α-Al₂O₃)

Abstract

Grain boundary microstructures in a commercial 99.8% alumina ceramic have been analysed using transmission electron microscopy. Nearly all boundaries are wet by an amorphous film which should invalidate both the CSL and DSC lattice constructions. Facets of widely differing sizes are observed primarily on basal {0001}, rhombohedral {1012}, and prism {1120} planes. The facets are always multiatomic in height and range up to ∼ 1000 Å; this probably results from substantial anisotropy in the Al₂O₃-glass interfacial energy. Basal annealing twins are observed without amorphous films; they lie predominantly on {1120} and show interfacial energies much lower than adjacent random boundaries.