VAPOR-PHASE GROWTH OF ORTHORHOMBIC MOLYBDENUM TRIOXIDE CRYSTALS AT NORMAL-PRESSURE OF PURIFIED AIR

Platelet crystals of molybdenum trioxide have been grown by a new simp le vapour phase method using a purified air at normal atmospheric pres sure. The grown crystals are transparent and colourless. Using the XRD and FTIR methods, it is confirmed that platelet crystals have layered structure of alpha-MoO3 (orthorhombic). The nucleation-growth of crys tal 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 al ong axes of the crystal follows the hierarchy {0 0 1} > {1 0 0} > {0 1 0}. Four types of boundary planes are found along (0 0 1) 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 st ructure of alpha-MoO3 have been verified by the pyramid-like etch pits . The etching rate on {1 0 0} planes is slightly faster than that on t he {0 0 1}. Technical features of the current growth setting are also addressed. (C) 1998 Elsevier Science B.V. All rights reserved.