IMPURITY-INDUCED STRUCTURAL TRANSFORMATION OF A MGO GRAIN-BOUNDARY

A combination of atomic-resolution Z-contrast imaging and first-princi ples density-functional calculations are used to establish that Ca imp urities segregating to particular atomic columns in MgO grain boundari es induce a structural transformation. The presence of Ca in the bound ary structure is independently confirmed by electron energy loss spect roscopy. The calculated electronic structure indicates that stabilizat ion of the new boundary structure by Ca is a mechanical rather than an electronic effect. [S0031-9007(98)07367-0].