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Joining of melt-textured YBa2Cu3O7-δ (Y123) grains has been achieved without use of an external agent. The technique uses barium-cuprate liquid phase released from platelet boundaries to mediate the growth of Y123 at the interface between two grains. The epitaxial nature and high quality of the growth was determined by optical and transmission electron microscopy. The composition of Ba–Cu–O phases found in some parts of the joins was determined by electron probe microanalysis. A clean low-angle join was found to consist of a grain boundary with dislocation networks and facets. Transport critical current measurements on this type of join revealed strongly coupled behavior. The technique shows promise for the joining of melt-textured material for power engineering applications.
The growth of large, melt-textured Nd1+xBa2−xCu3O6+δ (Nd-123) crystals has been achieved by hot seeding and isothermal solidification under a 1% oxygen in nitrogen atmosphere. These crystals, which exhibit a sharp, faceted growth interface, were grown epitaxially from a small Nd-123 single crystal seed placed on the sample surface at elevated temperature. The growth length of the melt-processed crystal was directly proportional to the isothermal holding time (approximately 17 h), as is observed for the growth of YBa2Cu3O7−δ (Y-123). The variation of growth rate with undercooling for this material was linear, however, in contrast to the parabolic dependence observed for Y-123 crystals grown in air. The growth rate of Nd-123 under reduced oxygen was consequently lower than that of Nd-123 and Y-123 grown in air at relatively high values of undercooling. Evaluation of the experimental data against a solidification models suggested that the interface kinetics are responsible, at least in part, for the observed growth features in hot-seeded Nd-123 crystals. This was attributed to the difference in oxygen partial pressure under the respective growth atmospheres, rather than to the species of rare-earth element in the compound.
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