A combination of atomic-resolution Z-contrast imaging and first-principles density-functional calculations were used to establish that Ca impurities, upon segregating to particular atomic columns in the grain boundaries, induced a structural transformation. The presence of Ca in the boundary structure was independently confirmed by electron energy-loss spectroscopy. The calculated electronic structure indicated that stabilization of the new boundary structure by Ca was a mechanical rather than an electronic effect.

Impurity-Induced Structural Transformation of a MgO Grain Boundary. Y.Yan, M.F.Chisholm, G.Duscher, A.Maiti, S.J.Pennycook, S.T.Pantelides: Physical Review Letters, 1998, 81[17], 3675-8