The influence of temperature gradients on structural perfection of single-crystal sillenite fibers grown by the LHPG method
Single-crysta fibers of Bi 12SiO 20 and Bi 12TiO 20 up to 90 mm in length with diameters of 200-1200 μm were pulled along the <001> and <011> crystallographic axis by the LHPG method. The powder X-ray diffraction and the electron-probe microanalysis were used for characterization of the grown fibers. The microstructure of sillenite fibers was studied by the chemical etching method. The dislocations, inclusions and striations are the main imperfections that were found in the fibers. The dislocation density equal to 1×10 5 pits/cm 2 was estimated on the ground of the etching pits using optical and electronic microscopy and was compared to that evaluated by the Tsivinskii's relation based on the axial temperature distribution in the fiber and on the elastic properties of the material. The conditions of the formation of microdefects are discussed in relation with the growth conditions, morphology and chemical composition of the grown fibers.