Growth of melt-textured Nd-123 by hot seeding under reduced oxygen partial pressure

Abstract

The growth of large, melt-textured Nd_1+xBa_2−xCu₃O_6+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 YBa₂Cu₃O_7−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.