Residual stresses in sapphire rods grown by the Stepanov method

The residual stresses in cylindrical [0001] sapphire crystals have been studied using the polarization-optical method. The angle between the optical axes 2V and the difference in the normal components of the tensor of elastic residual stresses $(\sigma_\varphi-\sigma_r)$ have been determined from the isogyre divergence. It has been found that a tangential tensile stress of no more than 20 MPa acts on the ingot surface. The residual stresses have been compared with the calculated thermoelastic stresses generated during the crystal growth in a given heating zone. It has been shown that the determined pattern of residual stresses can be caused by thermoelastic stresses developing in the immediate vicinity of the crystallization front.