Temperature gradient method (
TGT) is determined by China Institute of Optics and Fine Mechanics , Chinese Academy of Shanghai Zhou Yongzong et al in 1980 in order to achieve a first orientation of the seed crystal growth induced by the vertical temperature gradient method. Temperature gradient method is based on directional single seed -induced melt crystallization method . Including placing it in a simple bell-type vacuum resistance furnace crucible , heating element and shielding device 14 is a device diagram . This device uses americium crucibles, graphite heating element . Crucible bottom center of a seed tank, avoid hoe up soil around plants in the chemical feed grain were melted down when . In order to increase the stability of the crucible , the seed rod in the positioning groove fixation circular groove. Temperature field by a graphite heating element and cooling devices together provide . Heating body is cut into a rectangular wave by the upper and lower grooves of the cylindrical power circuit strip , mounted on the cylinder water-cooled graphite electrode connected to the electrode plates . The upper slat punching according to certain rules to regulate the heating resistor so energized causing near-linear temperature difference from top to bottom . The lower temperature by the heat generator and the water-cooled graphite heating element to create a conductive electrode plate . Temperature field near the seed must rely on water-cooled crucible together provide heat conduction rod . Schematic diagram of the temperature gradient method .
Main features of the method :
1)
Crystal growth temperature gradient opposite to the direction of gravity , and the crucible , the crystal and the heating body is not moving , the crystal growth interface stability, no mechanical perturbations , buoyancy convection is small;
2)After
crystal growth,surrounded by the melt , is still in the hot area, which can be precisely controlled cooling rate , reducing the thermal stress;
3)
Crystal growth,surrounded by solid-liquid interface in the melt , thermal disturbance before reaching the solid-liquid interface can be reduced and even eliminated interface for Uniform temperature gradient;
4)Crystals grown larger , it is difficult to create a good environment temperature field , the crystal easy to burst;
5)Respectively crystal blank to high temperature oxidation, reduction annealing
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| crystal growth |
atmosphere , the blank subsequent treatment process more complicated. Zhou Yongzong etc. using this method has grown out of the diameter ¢ 100mm, ¢ 110mm, ¢ 120mm high quality sapphire crystal. Temperature gradient method grown sapphire crystal , crystal showing different colors in different parts of the general upper light red, light yellow green tail . The crystals were through the oxidizing atmosphere , reducing atmosphere annealing , the crystal colorless , transparent crystal integrity , the optical transmittance and optical homogeneity significant Increased. Crystal growing apparatus before and after annealing the crystal shown in Fig.
1.Insulation boards;2.Heating element;3 Crucible;4.Graphite electrode;5.Cooling Pipe
