Atomistic simulation of the surface structure of spinel

Abstract

We present the results from a recent study of the structure and energies of the low-index surfaces of spinel IMgA1,04) using atomistic simulation techniques. These illustrate the complexity of modelling the surfaces of ternary oxides, particularly since cation ordering, resulting in the formation of inverse spinel, plays a crucial role in determining the relative surface stability. The simulations show some agreement with the very limited experimental data available for the spinel class of compounds. However, agreement with the most common experimental morphologies requires the consideration of kinetic factors.

Noncontact atomic force microscopy imaging of atomic structure and cation defects of the polar MgAl2O4(100) surface: Experiments and first-principles simulations

“…1(b) and 1(c), respectively, creating an Mg or O 4 -Al 4 -O 4 -terminated surface. Both (100) terminations expose so-called polar surfaces when cleaved stoichiometrically, and previous theoretical studies have calculated the surface energy of these different terminations 7,[10][11][12]14,25 and also estimated the percentage of atoms that need to be removed in order to fulfill the polar stabilization criteria. 26 In a simple picture, the Mg 2 and O 4 Al 4 O 4 stacks can be regarded as a series of layers with alternating charge of equal magnitude analogous to a series of capacitors, each holding a certain charge density.…”

“…7 Magnesium aluminate (MgAl 2 O 4 ) is a ternary metal oxide with the spinel crystal structure, which defines a larger group of so-called spinel minerals, with the general formula A 2+ B 2 3+ O 4 2− . 8,9 Most previous results addressing the issue of surface structure were based on theory, [10][11][12][13][14][15] and only a very few experimental studies have been presented. Yanina et al used contact mode atomic force microscopy to investigate the stages of surface faceting and coarsening of MgAl 2 O 4 (100) samples exposed to very high temperatures.…”

Configurational and energy study of the (100) and (110) surfaces of the MgAl2O4spinel by means of quantum mechanical and empirical techniques

“…This finding is in agreement with the previous ones. [12][13][14] Always concerning the configurational analysis, it is advisable to treat the crystal surface as a crystallographic entity and not exclusively as a chemical system lacking of whatever symmetry. As a matter of fact, when a crystal face is studied, it is fundamental to specify the symmetry elements preserved, if any, in the different surface configurations, as well as the cell parameters of the 2D cell considered.…”

“…[12][13][14] In all of these works, only stoichiometric surfaces (that is surface reconstructed to cancel out the dipole moment) were taken into account and a restricted number of (100) surface configurations were analyzed; unfortunately, in these papers there are not sufficient information and detailed figures that allow to understand and analyze the structure of the surface configurations. In detail, van del Laag et al 12 have described only two surface configurations (Mg-and Al-terminated), whereas Fang et al 13 In this paper, we will deal with stoichiometric surfaces at 0K in vacuum and we will show that the number of surface configurations detected in the previous papers is not sufficient to give a correct description of the structural complexity of a crystal face of MgAl 2 O 4 spinel.…”

Structural and magnetic properties of [001] CoCr2O4 thin films

“…The roughening of the surface results in a larger surface area, but the {111} spinel surface is found to be energetically favorable due to changes in the layer spacing at the surfaces, cation inversion, or surface reconstruction [45][46][47].…”