Effect of La-doping on growth and superconductivity of Bi-2212 crystals

Abstract Single crystals of the layered superconductor Bi 2 Sr 2 (Ca 1− x La x )Cu 2 O 8+ δ were successfully grown out by a self-flux method. Upon La-doping, the c -axis contracts but the structure remains stable up to the critical concentration x c , above which the crystals contain the pure Bi 2 (Sr,La) 2 CuO 6 phase. The reduction of the superconducting transition temperature follows a linear relation, T c ( x )= T c (0)(1− x / x c ), with x c =0.3 being consistent with the structure data. This, and a comparison with literature data on Pr 3+ - ( x c ≈0.65) and Y 3+ -doping ( x c =1), indicate an intimate relation between structural and superconducting stability in the 2212 phase. Besides the widely discussed hole-filling effect, the structural instability due to the substitution of large La 3+ for Ca 2+ is considered to be another contribution to T c suppression in this system.