Effect of Ti Doping on Structural and Superconducting Property of YBa_2Cu_3O_(7-y) High T_c Superconductor

摘要

Dimensional fluctuations of superconducting order parameters in YBa_2(Cu_(1-x)Ti_x)_3O_(7-y) (x = 0.01, 0.02, 0.04, 0.05) have been analyzed. SEM micrographs reveal the reduced grain size and the formation of TiO_2 nanowires covering over the grains of YBCO matrix. XRD graphs show the unchanged orthorhombic structure. With the increase of TiO_2%, it is found that the superconducting transition temperatures determined from standard four-probe method decrease gradually. Excess conductivity fluctuation analysis using the Aslamazov-Larkin model fitting reveals transition of two dominant regions (2D and 3D) above T_c. 2D to 3D crossover temperature, i.e., the Lawerence-Doniach temperature that demarcates dimensional nature of fluctuation inside the grains is influenced by Ti incorporation in YBCO matrix. The decrease in the Lawerence-Doniach temperature in the mean field region has been observed as a consequent dominance of 3D region with increase in Ti%.