SURFACE VACANCIES IN CLOSE PACKED CRYSTAL-STRUCTURES

The structure of the crystal surface is considered in relation to that of the underlying lattice. A description of those crystal structures which can be derived by partial occupancy by cations of the included holes in predominantly close-packed anion sub-lattices is given. Then, the surface structures which can be obtained by cleavage of stoichiometric crystals are discussed in some detail. The structure of the surface is shown to be dependent upon the underlying lattice. The nature and symmetry of the incompletely coordinated surface anions and cations are found to be a function of the crystal face exposed. Imperfections in the bulk structures are shown to influence the nature of the surface vacancies at and near the points of emergence of the imperfections. The nature of surface patches and domains is illustrated. The formation and growth of crystal surfaces are briefly discussed. Finally, the influence of the surface symmetry upon the energies of the cation d orbitals is considered, and the complex consequences of adsorption are illustrated by reference to spinel and molybdenite surfaces. © 1979.