Geometry of {001} Surfaces of Spinel (MgAl ₂ O ₄ ): First‐Principles Simulations and Experimental Measurements

Abstract

The geometry of {001} surfaces of spinel (MgAl 2 O 4 ) was investigated by first‐principles 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/m 2 for the relaxed (001)‐Mg surface and about 3.0 J/m 2 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.