Vapour phase growth of orthorhombic molybdenum trioxide crystals at normal pressure of purified air

Abstract

Platelet crystals of molybdenum trioxide have been grown by a new simple vapour phase method using a purified air at normal atmospheric pressure. The grown crystals are transparent and colourless. Using the XRD and FTIR methods, it is confirmed that platelet crystals have layered structure of α-MoO3 (orthorhombic). The nucleation-growth of crystal can be described by a two-dimensional layer-by-layer mechanism, in view of presences of ledges, kinks, terraces, and islands on {0 1 0} surfaces. Morphological study indicates that rates of planar growth along axes of the crystal follows the hierarchy {0 0 1} > {1 0 0} > {0 1 0}. Four types of boundary planes are found along directions: {0 0 1}, {1 0 1}, {1 0 2}, and {2 0 1}. Defect distribution has been investigated with 0.1 M NaOH. Crystallographic symmetry and layered structure of α-MoO3 have been verified by the pyramid-like etch pits. The etching rate on {1 0 0} planes is slightly faster than that on the {0 0 1}. Technical features of the current growth setting are also addressed. © 1998 Elsevier Science B.V. All rights reserved.