HYDROTHERMAL SYNTHESIS OF Bi_4Si_3O_(12) AND Bi_4Ge_3O_(12) CRYSTALS

摘要

Visually homogeneous eulytite-type Bi_4Si_3O_(12) (BSO) and Bi_4Ge_3O_(12) (BGO) crystals with sizes of 1-5 mm have been synthesized by spontaneous nucleation in hydrothermal NH_4F and HClO_4 solutions. BSO crystals have also been obtained on the seeds of Czochralski grown Bi_4Ge_3O_(12) crystals. Elevated concentrations of halogenide solutions promote other phases, like BiOF and/or BiOCl, to crystallize. Growth rate of BSO and BGO crystals increases with increasing concentration of solvent, crystallization temperature and temperature gradient. The synthetic eulytite crystals tends to grow with strongly developed {211} and {-2-1-1} faces. There is the following correlation between the growth rate of different faces of the BGO crystals: V_({211}) ≤ V_({-2-1-1}) < V_({310}) < V_({110}). External and internal morphology of these synthetic materials is similar to their natural prototype, and it is an easy way for identification of the simple forms in this mineral.