The surface of MgO periclase

Periclase (MgO) has the rocksalt structure, which is face-centered cubic with each Mg-+ cation surrounded by six 0 anions in a regular octahedral arrangement, and each O similarly coordinated to six cations at the corners of a regular octahedron. By far the most stable surface for oxides having the rocksalt structure is the (100), illustrated in Fig. 8.13 

Rutile has a tetragonal lattice in which Ti ions occur coordinated to ions in slightly distorted octahedral sites, one-half of the octahedral sites being empty. The most stable crystal face appears to be the (110), and in Fig. 8.16 is shown the (110) surface that results from breaking the smallest number of cation-anion bonds (after Henrich, 1983, 1987). Two kinds of Ti cation are present on this surface, one with five ligands and one with all six ions, as in the bulk material. The local environment of the five-coordinated cation is similar to that of the surface cation in MgO. 

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