GROWTH OF [[alpha]]-Al₂O₃ BICRYSTAL BY BRIDGMAN METHOD.

E. K. Kov'ev, B. M. Allaudinov, Crystallography Institute Russian Academy of Science, M. Yu. Kupriyanov, S. N. Polyakov, Institute of Nuclear Physics Moscow State University. The development of modern cryoelectronics based on HTS Josephson junctions demands the fabrication of high quality [[alpha]]-Al₂O₃ bicrystal substrates. Unfortunately the solid-phase intergrowing method usually used for its fabrication gives a large density of active aluminum atoms in the vicinity of the boundary. This results in degradation of the basic parameters of the HTS Josephson junction made on [[alpha]]-Al₂O₃ bicrystal substrates. The alternative is to use naturally grown bicrystal for the substrates fabrication. In this paper we reported the main result in the development of the new technology for growth the [[alpha]]-Al₂O₃ bicrystals by horizontal Bridgman method using universal apparatus "Sapphire-2". The crystals with typical size 150õ90õ20mm and average velocity of the crystallization 10mm/h were grown in a specially design Mo bath by two-seeds method.

The crystallization fronts during growth process are coincide with [112^-0] directions. The inclination angles 2[[theta]] of the symmetrical boundary are closed to 24⁰, 28⁰, 36⁰. The R and M-planes is used as a bicrystal surfaces. The special manipulator has been developed for control the orientation of the parts of the seed bicrystal with the accuracy better that 0.3⁰ in all three crystallographycal directions. The quality of the bicrystals was investigated by X-ray diffraction, optical and electron microscopy methods. It was found by X-ray diffractometry that the missorientaton angles in three crystallographic directions has the accuracy 0.5⁰. The full width at half maximum of the rocking curve (101^-2), (101^-0) and (1202) reflections near the boundary closed to 20-30 arc. sec. The structure of the dislocations and microcracks formation in the vicinity of the bicrystal boundaries are investigated.