Impurity segregation to the surfaces of corundum-structured oxides

Atomistic computer simulation methods have been used to calculate iso- and alio-valent segregation energies in the corundum-structured oxides Al sub 2 O sub 3 and Cr sub 2 O sub 3 . The results show that the assumption made in the Langmuir isotherm, i.e. that the heat of segregation is coverage-independent, is not generally valid and that segregation is often both coverage-dependent and highly surface specific. The heats of segregation for Ca at the basal and prism planes of Al sub 2 O sub 3 and yttrium at the low index, and Mg and Fe at basal plane of Cr sub 2 O sub 3 are given. Comparison with available experimental data is given, showing good agreement for a Ca on the prism plane of Al sub 2 O sub 3 . 15 ref.--AA