Development of a New Crystal Growth Technique using Preitectic Reactions

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Peritectic reactions which are commonly observed upon solidification of incongently molten liquid have been applied for growth of large oxide crystals. Recrystallization under the Ostwald ripening mechanism proceeded in keeping of such a peritectic condition where peritectic solids coexisted with liquid. Small particles with peritectic layrs tended to diminish by resolution into the melt due to high surface free energies and large, well-habited crystals surrounded by developed surfaces with infinit curvatures became large. The merits of using this technique are that materials with high melting, high vaporizing or incongruent melting properties can be crystallized, that the growth procedure is so simple as usual flux methods and that undesired contamination from crucible materials can be avoided because of low growth temperatures. Here we applied this technique to oxides such as oxide superconductors and low dimensional oxides, and succeeded in growing mm-sized, high quality crystals of YBa_2Cu_3O_x, Tl_2Ba_2Ca_2Cu_3O_<10>, Tl_2Ba_5Cu_4O_<x, > SrCuO_2, Y_2Cu_2O_5, CuFeO_2, PdCoO_2 PtCoO_2 and MgSiO_3. Using these crystals, we measured the crystal structures, magnetic and electric properties. To clarify the growth mechanism more precisely, we have constracted a high temperature X-ray diffraction apparatus with a rapid counting system for analyzing the phase change rates in peritectic conditions. The results indicated that the diffusion in the liquid phase was the rate determining process rather than in the soild phase. Detailed phase relations in the Bi-Sr-Cu-O,Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O systems have been also established between 1273K and room temperature using the same spparatus in air.