The effect of grain size on the fluctuation-induced conductivity of Cu_1−<i>x</i>Tl_<i>x</i>Ba₂Ca₃Cu₄O_12−δsuperconductor thin films

Abstract

The high temperature superconductor thin films Cu1−xTlxBa2Ca3Cu4O12−δ (Cu1−xTlx- 1234) are post-annealed in a nitrogen atmosphere. The zero-resistivity critical temperature (Tc(R = 0)) of these thin films is increased from 92.3 to 104 K. The grain size is enhanced and their morphology is improved with the post-annealing. The enlargement of grain size is linked to fluctuation-induced conductivity (FIC) in the light of Aslamazov–Larkin (AL) theory. The FIC measurements have shown that the cross-over of three-dimensional (3D) to two-dimensional (2D) behaviour of fluctuations is shifted to higher temperature values with an increase of post-annealing temperature. These results have shown that the removal of oxygen and the increased grain size are the most likely sources of the increase in the cross-over temperature, T* to higher values.