THE DEVELOPMENT OF THE IN SITU OBSERVATION OF CRYSTAL GROWTH: THE RELATIONSHIP BETWEEN LINEAR AND MASS GROWTH RATES. L.V.Yashina, V.I.Dernovsky, V.P.Zlomanov, Moscow State University

This report is devoted to in situ control of crystal growth rate and habit in the case of A(IV)B(VI) compounds grown from the vapor. Among different in situ methods the observation of linear crystal size is most attractive. It can be much more accurate then mass measurement, especially for small crystals. It is easy to control by computing. As a result of such measurement the kinetic curve l(t) would be obtained. The statistical treatment of this curve can be in form l=a+bt^c, where c is the order of kinetic curve, a connected with error in the growth beginning moment, b expresss the growth rate. The order c is sensitive for limiting stage. If crystal shape is changed during experiment the determination of the limiting stage by order c can be incorrect.

To obtain the total information from the in situ experiment it is need to calculate the linear parameter to crystal mass. That is to calculate habit constants q=Vd /l³, q = S/l² , where V - crystal volume, d - density, S - crystal surface aria. We describe the total majority of polyhedral habits for PbTe and GeTe crystals. For PbTe habit is realized as parts of cube (12 types), the cross section coinciding with quartz surface. For GeTe crystal habit is realized as truncated cubooctahedron and rombohedron. If habit constants are known it is possible to evaluate condensation and diffusion coefficients from kinetic curve by equation. In our experiments with PbTe and GeTe the good agreement between parameters obtained from both integral measurements and kinetic curves take place. The deviation of final experimental habit constants from calculated connected with the instability of crystal shape. So detail analysis of kinetic curves l(t) is attractive instrument for crystal growth study.

These results can be useful for small size (1-2 mm) crystals

preparation.