Abstract
The Top-Seeded Melt-Growth process for preparation of bulk YBCO single-grain samples from the nominal composition 1mol YBa2Cu3Ox, 0.25mol Y2O3 and 1wt% CeO2 was analysed by optical and electron microscopy, EDAX microanalyses and thermal analyses. It is shown that 4.2wt% of CuO is formed after reaction of constituents. During an isothermal dwell at the optimised temperature, the growth of Y123 single-crystal stops due to decreasing peritectic temperature with increasing CuO concentration in the melt. The growth at furnace cooling leads to trapping of droplets of melt into the growing crystal, which finally epitaxially crystallises on Y123 as BaCu2O2 phase. The last part of the sample solidifies as Y123 elongated spheroids with Y211, BaCu2O2 and CuO phases. Additional slow cooling 1°C/h from the temperature of isothermal growth leads to epitaxial growth of Y123 crystal over the entire sample. Only very narrow part at the rim of the sample contains CuO phase and blocky Y123 crystals are formed there due to self-nucleation.
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