Crystal growth in the directed solution flow byin situAFM-observations

Abstract

Mixed crystal formation is characterized by specific phenomena and mechanisms what is urgent to reconstruct a mineral origin and to grow such crystals. The following processes including their joint development are observed in supercooled mixed solutions: dissolution, replacement, metastable heterogeneous equilibrium, and direct growth. A thermostatic vessel was used for visual observations and quantitative measurements of the processes in the ternary aqueous system with Co-Ni Tutton salts. Volume-deficit and volumeexcess replacement reactions were investigated during the interactions of the various mixed solutions and the end-member crystals of the isomorphic series. The phenomena mechanisms are interpreted in terms of the concept of multimineral-metasomatic crystallogenesis with help of modified Schreinemakers phase diagrams. Such combined morphological-kinetic investigations of mixed crystal formation are carried out for the fist time. In a general case of mixed crystal formation the ratios of the replacement and growth varies in a wide range depended on the crystal/solution compositions and the supercooling. A replacement is changed by a growth the faster the supercooling is higher. The characteristic supercooling of the growth without a replacement stage (the position of the metastable equilibrium) the versus the solution composition reaches a maximum around the equal quantity of the isomorphic components in the solution. In the case of a pure isomorphic replacement in a solution saturated by another isomorphic component, the rate of the process is slowed down during the course for all the solution compositions. These processes cause formation of unordinary spongy-like and epitaxy-excrescenced pseudomophs at volume-deficit and volume-excess replacement reactions respectively. Keywords: CRYSTALLOGENESIS, ISOMORPHISM, MINERALOGY Acta Cryst. (2002). A58 (Supplement), C168GROWTH AND POLING OF BATIO3 SINGLE CRYSTALS T.K. Lee H.J. Park S.J. Chung Seoul National University School of Materials Science and Engineering Gwanak-Gu Shinlim-Dong San 56-1 SEOUL 151-742 SOUTH KOREA BaTiO3 single crystals were grown by the top-seeded solution growth technique. The solution was composed of 33.5 mol% BaO and 66.5 mol% TiO2. The observed surface roughening temperature was in the temperature range of [1370][1371][1372][1373][1374][1375][1376][1377][1378][1379][1380] o C in this solution. The grown crystals were yellowish, transparent and about 2-3 cm in size. The spatial domain configurations in the grown crystals were observed under a polarizing microscope, transmission electron microscope and by X-ray topography.In the poling process of the grown crystals, pressing, heating and applying of electric field were taken simultaneously according to a poling schedule on a house-made poling apparatus. The elimination of 90° domain boundaries could be confirmed under a polarizing microscope.The refractive indices of as-grown crystals and the poled crystals are compared each other to examine the quality of the grown crystals. The dielec...