Lukienko O. Defect structure of sapphire grown by the of horizontal directed crystallization method, which is formed at increasing the crystal dimensions

The work is devoted to the establishment and characterization of crystal structure defects, which are formed in sapphire of grown by the horizontal directed crystallization method (HDC) at transition from the size of 200×200×30 mm3 to 300×230×30 mm3. It is established that in 300×230×30 mm3 crystals grown by the (HDC) method contain randomly distributed regions with values of internal stresses of 4 MPa and more. There regions are caused by the existence of small angular dislocation torsion boundaries mismatched within 5-50 arc seconds. The angles of mismatching between the blocks in the grown crystals are ranged 1 to 5 degrees, which leads to the formation of structurally inhomogeneous regions with a cross section of ~ 1 mm and a length of few cm. The dependences of the integrated X-ray reflection intensity on the dislocation density ρ for the crystallographic planes , , , are obtained. An anomalous X-ray propagation (Bormann effect) in 300×230×30 mm3 sapphire grown by the HDC method was observed for the first time. The integral absorption coefficient of an abnormally X-ray beam μi and the thickness of sapphire (0,45-1,50 mm) where X-ray scattering is described by dynamic theory, were experimentally determined. Data on the defect structure of 300×230×30 mm3 sapphire were used by technologists to improve crystallization units. It increased the yield of the perfect crystals to 70-80%. Keywords: sapphire, horizontal directed crystallization method, defects of crystal structure, X-ray diffraction.