Phenomenon of thermal-field jumps in growth of single-crystal sapphire ribbons by the Stepanov and horizontal directional-crystallization methods

The phenomenon of thermal-field jumps in bulky single-crystal sapphire ribbons grown by the Stepanov and horizontal directional-crystallization methods is observed. Considerable jumps of thermal fields with up to 4-min duration and a 50degreesC amplitude were recorded at a distance of 40 mm from the crystallization front of ribbons grown by both methods. As a result, the crystals had considerable nonstationary thermoelastic stresses that could give rise to the formation of blocks and other structural defects. The jumps revealed considerably exceeded the noise level of the measuring system. Possible causes of oscillations of the radiative heat flow along an optically transparent sapphire crystal are considered. (C) 2004 MAIK "Nauka/Interperiodica".