Observation of curious spiral growth features in Tl doped Hg bearing high temperature superconducting tapes

Synthesis of Hg(Tl)Ba 2Ca2Cu3O8+δ superconducting tapes have been accomplished by annealing the precursor tape, Ba2Ca2Cu3Oy (fabricated by doctor blade tape casting technique) in an environment of Hg(Tl) vapour. Characterization of superconducting HTSC tape sample was carried out through XRD, TEM, SEM and R-T measurements. Surface morphological investigations of the as -synthesized Hg(Tl)Ba2Ca2Cu3O8+δ HTSC tapes by scanning electron microscope have shown the occurrence of curious growth characteristics resembling spiral like features. These growth spirals encompass nearly the whole grain suggesting that spiral growth led to the formation of small crystal like grains of superconducti ng material Hg(Tl)Ba2Ca2Cu3O8+δ. The likely mechanism for the generation of these screw dislocations has been elucidated in terms of incoherent coalescence of growth fronts formed from Hg(Tl):1223 and Hg(Tl):1234 nuclei.