Growth mechanism and growth habit of oxide crystals

In this paper, the growth mechanism and growth habit of oxide crystals are investigated. Firstly, from the kinetics viewpoint, the growth mechanism of ZnO powders under hydrothermal condition is disclosed starting from the hypothesis of growth unit. It is concluded that the growth mechanism of oxide crystals contains the formation of growth units and the incorporation of growth units into the crystal lattice by a dehydration reaction. Then, a new growth interface model of oxide crystals in solution is established on the basis of an ideal growth mechanism of oxide crystals, which considers the interface structure of the crystal as the stacking order of coordination polyhedrons with OH- ligands. Finally, a new rule concerning the growth habit is deduced considering the relation between the growth rate and the orientation of the coordination polyhedron at the interface. It is concluded that the direction of the crystal face with the corner of the coordination polyhedron occurring at the interface has the fastest growth rate; the direction of the crystal face with the edge of the coordination polyhedron occurring at the interface has the second fastest growth rate; the direction of the crystal face with the face of the coordination polyhedron occurring at the interface has the slowest growth rate. In terms of this rule, the growth habit of ZnO crystal particles and AlO(OH) crystal particles, and the effect of reaction medium on the growth habit are successfully explained. (C) 1999 Elsevier Science B.V. All rights reserved.