ChemInform Abstract: Crystal Growth of Mg2SiO4 and MgSiO3 Single Crystals by the Flux Method.

Abstract

Single crystals of Mg2SiO4 and MgSiO3 have been synthesized by the evaporation-aided slow-cooling flux method. Acidic oxides such as V2O5, MoO3, and WO3 were used as the flux, and alkali metallic oxides or calcium oxides were added to the MoO3 and WO3 as flux modifiers. The starting mixture was first held at 1400°C and then slow cooled to 1000°C at a rate of 10 C/h. The temperature difference between the upper and lower limits of the melt was ∼25°C. Using an Li2O─MoO3 system flux with an Li2O:MoO3 ratio of 1:2 produces a polycrystalline clinoenstatite with a 9-mm crystal size; a 1:1 ratio, however, results in forsterite crystals of 90-μm size. The metallic oxides (Na2O and K2O) as flux modifiers produce forsterite with a crystal size of 65 and 40 μm, respectively. Similar results are observed when a Li2O─WO3 flux is used. Enstatite (10-mm size) and forsterite (1.6-mm size) are produced when the Li2O:WO3 ratios are 1:2 and 1:1, respectively. A V2O5 or CaO·WO3 flux produces no forsterite. The V2O5 flux results in tridymite as a primary phase, whereas calcium and magnesium tungstate were grown from a CaO·WO3 flux. The forsterite single crystals are tabular in form, generally bounded by the planes (001), (100), (010), (110), and (021), and are transparent. The enstatite consists of an aggregation of individual single crystals. The refractive indexes of the forsterite are α= 1.636 ± 0.001, β= 1.653 ± 0.001, and γ= 1.671 ± 0.001 (20°C).