abstract
The effect of the intensity of the direct electrical current on the morphology and properties of superconducting BSCCO fibres grown by the electrically assisted laser floating zone (EALFZ) technique is presented. Stereological analysis and x-ray diffraction (XRD) pole plots reveal textural enhancement and crystal refinement as the main features when the current intensity increases. Analysis with scanning electron microscopy/energy dispersive x-ray spectroscopy also discloses changes in the phase fraction and nature. Improvement of the grain alignment is a result of the intensification of ionic migration in the solid-melt interface along the fibre axis. This leads to a net increase in the length of primary dendrites and a reduction in dendrite thickness and interdendritic spacing. The increase in current intensity also favours the vanishing of the 2201 phase and of the residual melt. The development of the 2223 phase during isothermal annealing is very pronounced for the EALFZ fibres grown under high current intensities due to the refinement of the reactant phases. The current transport capability after isothermal annealing of fibres is improved with application of a low current intensity (50 mA), reflecting a net change of the morphological characteristics. However, when a high current intensity (200 mA) is applied the unfavourable orientation of the newly formed 2223 crystals and the loss of crystallite quality of the 2212 phase due to intergrowth of 2223 structure in the original 2212 structure lead to poor superconducting properties.
keywords
INTERFACE; GROWTH
subject category
Physics
authors
Carrasco, MF; Soares, MR; Amaral, VS; Vieira, JM; Silva, RF; Costa, FM
our authors
Joaquim Manuel Vieira
Retired Professor
Maria do Rosário Teixeira Soares
Laboratory Officer
Rui Ramos Ferreira e Silva
Associate Professor