Geometry of {001} surfaces of spinel (MgAl2O4) : first-principles simulations and experimental measurements

The geometry of {001} surfaces of spinel (MgAl2O4) was investigated by first-principle simulations within density-functional theory (DFT). The calculations show that the structure relaxation or reconstruction occurs for a depth of about 0.5 nm. The (001)-Mg surface shows moderate relaxations and the (001)-Al surface shows reconstruction: a new surface was formed with half of the subsurface oxygen atoms moved to the top. The surface energy was calculated to be about 1.7 J/m2 for the relaxed (001)-Mg surface and about 3.0 J/m2 for the relaxed (001)-Al surface.The chemical composition of a freshly fractured (001) surface of a spinel single crystal was measured using Low Energy Ion Scattering. The measured Al/Mg ratio indicates that the (001)-Mg surface is more stable, in good agreement with the calculations.