THE RELATION BETWEEN TEMPERATURE-GRADIENTS AND STRUCTURAL PERFECTION OF SINGLE-CRYSTAL BI12SIO20 AND BI12TIO20 FIBERS GROWN BY THE LHPG METHOD

The axial temperature distribution in the sillenite fibers was calcula ted based on the elastic properties of the material. The dislocation d ensity was evaluated by the Tsivinskii's relation and compared with ob tained by the chemical etching method on single-crystal Bi12SiO20 fibe rs grown the LHPG method. It was shown that BSO fibers will crack due high axial temperature gradients if the fiber diameter exceeds some cr itical value D-crit. The relation between the temperature gradients an d the structural perfection of the as-grown fibers and the ways of the optimization of the temperature distribution during the fiber growth process has been discussed.