Growth, microstructures, and superconductivity of Bi_(2-x)Pb_(x)Sr_(2)Ca_(1-y)Gd_(y)Cu_(2)O_(8+z) single crystals

摘要

Bi_(2-x)Pb_(x)Sr_(2)Ca_(1-y)Gd_(y)Cu_(2)O_(8+δ) (x=0.34 and y=0.18, 0.34) crystals were grown by the self-flux method. The crystals have a cleavage thickness of only half unit cell up to two unit cells with T_(c) only dropping 20 K as y is increased from 0.18 to 0.34 for as-grown crystals. However, T_(c) increased to almost the same value of about 80 K after annealing in air regardless of the Gd doping levels. The co-doping produced enhanced flux pinning compared to the sole Gd doping. A secondary peak effect presented in crystals with x=0.34 and y=0.34 was explained by phase segregations containing Gd-rich clusters.