The seeding effect of floating zone growth on Nd1.85Ce0.15CuO4 and Bi2Sr2CaCu2O8-δ single crystals

Single crystals with the [100] orientation were selected and used as seeds to investigate the effect of travelling solvent floating zone growth on superconducting oxides of Nd1.85Ce0.15CuO4 and Bi2Sr2CaCu2O8-δ. The number of nuclei was remarkably reduced and random nuclei could be eased when the seeding was applied during the growth of Nd1.85Ce0.15CuO4 single crystals, compared to the crystals grown without seed. The crystal could preferentially grow on the seed although some additional nuclei occurred at the solid-liquid interface during the initial growth process. In consequence, the crystal ingot obtained is a large single grain having dimensions of 5 mm in diameter and 40 mm in length. The orientation of the seeded growth crystal was found to be 5deg off the [100] seed identified by an x-ray Laue pattern. For the growth of Bi2Sr2CaCu2O8-δ, it was found that the seed crystal was well melted to decompose and mix with the molten zone flux composition. This led to crystal growth in accordance with the spontaneous nucleation procedure. The chemical composition of the interface between the seed and the grown crystal was determined by EDX. The growth behaviour and crystal habit show no significant change from those when seed samples are not used. This indicates that seeding does not influence the growth of Bi2Sr2CaCu2O8-δ for this incongruent melt, i.e., neither seed-orientated nor size-improved crystal is obtained. The crystal size is seen to increase significantly and the number of grains is remarkably reduced with the length of the crystal ingot grown. The crystallographic directions of [100] and [010] are well aligned along the growth direction of the crystal ingot. The composition of the compounds and secondary phases were determined in the boundary region between the seed and newly grown crystals. The superconducting transition temperatures were also determined for the as-grown and post-annealed samples