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The impurity distribution in front of the surface of the growing crystal by Czochralski iiiethod is considered at the assuriiption t h a t the crystallization begins in the melt within the diffusion layer by the formation of clusters, i.e. it has a n extented nature. The moving force of the crystallization is the supercooling of the melt. The principle distinction from tlie classical BPS theory is that the concentration profile has no break near the meltc r p t ' a l interface and is defined by the impurity concentrations both in the liquid and cluster phases with allowance for their specific volumes. Tlie existing theories of crystal growth can be divided into two groups. To the first group belong the theories according to which growth processes are considered as the abrupt boundary phenomenon on atomic or molecular level. The second group of theories considers tlie crystallization process as an extended process carried out by means of accumulation of complex formations before the surface of the growing crystal. Direct diffraction investigations of metal and oxide melts have shown that even in melts superheated by tens of degrees the ordered volume structures of tens of Angstrom in size are kept.The extented nature of the crystallization process is proved by the growing quantity of experimental data. But the impurity distribution a t the crystallization and at the directional crystallization from the melt, in particular, is still described from the clawical notions about a sharp boundary between crystal and melt, and as a consequence, about tlie interrupted change of impurity concentration between solid and liquid in accordance with the distribution coefficient (Fig. 1, curve 1).I n the present paper we consider the impurity distribution before the surface of the groving crystal during directional crystallization from the melt supposing that thc crystallization begins in the melt within the diffusion layer by the formation of clusters, i.e. it has an extended nature. The existence of clusters is possibly even higher than tlie liquids line, but in this region the clusters are in dynamic equilibrium with the melt, and the bulk of the melt has the characteristic properties of a liquid.

The transformation from Y 3 Al 5 O 12 to perovskite YAlO 3 crystal phase was observed during ultrafast laser writing in the bulk of a Y 3 Al 5 O 12 single crystal. The control of the phase transformation was demonstrated by tuning parameters of laser writing. The phenomenon is interpreted in terms of structural changes in the overheated garnet melt under laser heating followed by rapid solidification, and at least 1-ms dwell time of overheated melt is required to start spontaneous crystallization. The appearance of the perovskite phase was confirmed by Raman spectroscopy, quantitative phase and polarization microscopies.