Growth and characterization of large crystals of GdBa2Cu3O7 superconductor

The growth of large crystals of Gd-Ba-Cu-O superconductor by using the K2CO3 method adopted earlier for preparing oriented ceramics and large crystals of Y-BaCu-O superconductors is reported. The temperature favourable for the growth of GdbaCuO crystals is found to be higher than that required for YBacuO crystals. Also, the crystal perfection is better for these crystals and as a result, the oxygenation of the sample becomes more difficult. Resistivity measurements on these samples show a sharp drop in resistivity at 90 K which than tails off at lower temperatures and attains zero resistance around 35 K. Such behaviour is normally due to an inhomogeneous oxygen content in the sample. Chemical analysis shows that the deviation from '123' composition in GdBaCuO-samples is much less as compared to YBaCuO-samples obtained by the same technique. (author). 32 refs., 3 figs