Analysis of thermal shock during rapid crystal extraction from melts

A time-dependent stress field in LiNbO3 and SrLaAlO4 single crystals immedi ately after their extraction from melts has been found analytically. Numeri cal calculations show that during rapid extraction from melts the crystals are subjected to thermal shock which can be high enough to produce consider able dislocation density if there exists a plasticity zone or to induce cra cks. During LiNbO3 crystal growth by the Czockralski method in a low temper ature gradient high thermal stresses occur near the interface at the center and at the crystal periphery. After rapid extraction from the melt the the rmal shock results in an increase in thermal stress over an order of magnit ude. This can lead to the generation of high dislocation density at the bot tom part of LiNbO3 crystal causing residual stress distribution after its c ooling to room temperature. Times for the relaxation of stresses caused by the thermal shock are about 30 minutes and 30 seconds for 55 mm diameter Li NbO3 crystal and for 20 mm diameter SrLaAlO4 crystal, respectively. The mag nitude and relaxation time of the stress caused by the thermal shock depend mainly on the crystal diameter, its thermal conductivity and the axial tem perature gradient in the growth system. From analytical investigations a su itable method of crystal extraction from the melt may be obtained.