Title: Crystal structural control on surface topology and crystal morphology of normal spinel (MgAl2O4)
Authors: Dekkers, Rob ×
Woensdregt, CF #
Issue Date: Mar-2002
Publisher: Elsevier science bv
Series Title: Journal of Crystal Growth vol:236 issue:1-3 pages:441-454
Abstract: Elementary growth layers and their related surface topologies of the spinel (MgAl2O4) have been defined by the application of the Hartman-Perdok analysis. The crystal structure of spinet is used as a model for all normal spinels. Four periodic bond chains (PBCs) have been found, i.e. <1/2 1/2 0>, <0 0 1 >, <1/2 1/2 1 > and <0 1/2 1 1/2>. They define five F forms , which are in order of decreasing d(hkl): {1 1 1}, {2 2 0}, {1 1 3}, {4 0 0} and {3 3 1}. For each of the elementary growth layers (slices) d(111), d(220) and d(400) we define two different slice configurations, of which the second configuration can be obtained from the first one by a translation over <1/4 1/4 0 >. Special attention is given to surface topologies, which can be ordered or disordered. More than one type of ordering is possible. Surface related energies such as attachment energies and specific surface energies of all above-mentioned slices, have been calculated in an electrostatic point charge model of spinel: Mg+0.945 Al-2(+1.475) O-4(-0.945). In this model not only Coulomb interactions, but also Born repulsion and van der Waals interaction energies have been taken into account. The theoretical growth form and the equilibrium form of spinel show an octahedral {1 1 1} habit. The energetically most favourable slice configuration consists of complete [AlO6] Lctahedra in its centre. On its surface a minimurn of At atoms are present, while Mg atoms are located just below the surface. These Al ions are ordered according to a [1 x 2] 2D superlattice. Another choice for the {1 1 1} slice configuration with complete [MgO4] tetrahedra as central ions and three times more Al ions on the surface is energetically much less favourable. Surprising was the result that one particular S face is relatively stable. This has been explained by the presence of complete [AlO6] octahedra within its slice boundaries and the low number of dangling Al-O bonds at its surface. (C) 2002 Elsevier Science B.V. All rights reserved.
ISSN: 0022-0248
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Department of Materials Engineering - miscellaneous
× corresponding author
# (joint) last author

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