Study On The Morphology Of Hydrothermal Bi₁₂SiO₂₀ Crystal

Bi₁₂SiO₂₀（BSO）, sillenite structure, body-centered structure of the cubic system, spacegroup is I23.BSO has piezoelectric, electro-optic, photorefractive, photoconductive,magneto-optical, acousto-optical, optical rotation and other properties. BSO is widely used inoptical information processing and sensor element. Czochralski has been the most commonmethod to grow BSO crystal. However many defects have been revealed in this crystal growthmethod, particularly to optical uniformity. Hydrothermal method has become an effective wayto grow a high quality BSO crystal. Because lack of the critical defect in hydrothermal BSOcrystal as compared to Czochralski and Bridgman-Stockbarger. This paper focuses on thecrystal morphology of the hydrothermal method BSO.In the paper, the hydrothermal BSO crystal has two different crystalline forms: thepolymorphs of {111} and {211}; the polymorphs of {100} and {110}. A analysis of twodifferent forms by use of the Bravais rules and the Donnell-Huck theory. The analysisindicate the relative growth rate and exposure degree of each faces. Preliminary discussion ofthe causes of change in crystal morphology occurs, a solution of the growing crystal oversaturation change, which changes the crystal morphology have a significant effect.Study on the crystal morphology and surface structures of two different crystalline habitsof hydrothermal BSO crystals with Differential Interference Contrast Microscope andinverted metallurgical microscope．There are Spheroid growth hillock on {100} faces; lots ofgrowth hillocks and growth steps on {110} faces; growth hillocks and striations-like growthsteps on {211} faces; and growth hillocks, growth steps and Spiral striation the threesymmetrical features on {111} faces.The morphology and surface structures of crystals of BSO crystal is to determine withPBC bonds during the crystallization process. There are two basic bonds in BSOcrystal:[100]PBC and [111]PBC. Parallel {110} crystal face has three PBC bonds,[100]、[111] and [11]PBC, an F face.The micromorphology accord with F surface characteristics.Parallel {100} crystal face has two PBC bonds,[001] and [010]PBC，an F face. Themicromorphology in line with F face characteristics,too. Parallel {211} crystal face has one[111] PBC bonds, an S face. The micromorphology in line with S face characteristics.{111}crystal faces has no PBC bonds, a K face. However, the micromorphology doesn’t in line withK surface characteristics but F face. In this case, the faces on {111} from K face wastransformed into F face. PBC theory is that there are some defects, the faces on {111} shift by the ambient.It can not be merge into the theory, so some phenomena can not be explained.HCL and CH3COOH mixture of solution were used to corrode BSO crystals. Theetching figures on {100},{110},{111}{211}face and sections have been studied. The etchingrate of the BSO crystal is fast, within2³min at room temperature The etching figures on{100} face is parallelogram; on {110} face is a square with the outline of, and each etchingfigure is not entirely consistent. The etching figure on this two faces both have a twofoldsymmetry characteristics; on {111} face and {211} face show a triple symmetrycharacteristics complex triangle. Using polar stereographic projection analysis etching figureto get its features consistent with crystal symmetry.