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Abstract

The top-seeded solution growth (TSSG) method has been modified
and developed for the growth of Y1-xCaxBa2Cu7-delta, single
crystals. The initial composition was investigated with a molar
ratio of Y:Ba:Cu = 1.0:7.2-24.0:11.8-54.0 plus additional Ca
used in the melt to maintain the growth in a constant
supersaturation. This allows crystals to grow Lit a constant
rate of up to 2mm/d for 100h. Crystal sizes of up to 15 x 10 X
8 mm(3) were obtained. The growth was carried Out in an oxygen
environment and air, respectively. The melt temperature was
found to increase significantly during the growth in oxygen
atmosphere. suggesting, that an increased crystallization
temperature was required in comparison with that of the growth
in air. Y-stabilized ZrO2 crucibles were used. The
concentration of Ca for the crystals was determined to be in
the range of x = 0.18-0.30. The Solubility of Ca in YBa3Cu3O7-
delta is low which means Ca is hard to incorporate into the
compound. The segregation coefficient of Ca for the compound
was estimated to be similar to0.7 which is smaller than unity.
The result of magnetic Susceptibility measurement showed a
broad superconducting transition due to the oxygen
insufficiency in the as-grown crystals. By post-annealing,
oxygen was taken over by the compounds, resulting in a sharp
transition width of 4 K. The superconducting transition
temperature T-c reduces with increasing Ca content. 75 K at x =
0.30, 78 K at x = 0.20 and 79 K at x = 0.19. The overdoped and
high-duality crystals could be grown by the TSSG method. (C)
2002 Elsevier Science B.V. All rights reserved.