Block structure and residual stresses in tubular sapphire single crystals grown by the Stepanov method

Abstract

The formation of the block structure and residual stresses in sapphire single-crystal tubes grown from the melt by the Stepanov method has been studied. The distribution of the difference in the residual stress tensor components (σφ–σr) in a thick-walled [0001] sapphire tube has been measured by the conoscopy method. It has been shown that circumferential tensile σφ and compressive stresses act on the outer and inner tube surfaces, respectively. The maximum stress is ∼20 MPa. It has been demonstrated that the development of the block structure begins from the outer tube surface; as the crystal length increases during growth, blocks propagate over the entire cross section.