CONDITIONS OF MAINTENANCE OF A FLAT CRYSTAL MELT INTERFACE DURING CZOCHRALSKI GROWTH OF BISMUTH GERMANIUM OXIDE SINGLE-CRYSTALS

Investigations of Czochralski growth of Bi12GeO20 and Bi4Ge3O12 single crystals in crucibles with different diameters and a constant crystal diameter/crucible diameter ratio d/D = 0.42 have been carried out. The effect of the change in height of the melt layer in the crucible on the temperature distribution in the melt and on the critical crystal rotation rate at which a flat crystal/melt interface is formed, is determined. The temperature dependences of the viscosity and density of the melts of the two bismuth germanium oxides and the values of their volumetric expansion coefficients are established from separate measurements. After a suitable processing of the experimental results it is shown that they satisfy the general correlation proposed earlier on the basis of model studies for the critical crystal rotation rate and the geometrical and physical parameters of the system crucible-melt-crystal.