Growth, Superconductivity and Anisotropy in the Electrical Resistivity of P b₂ S r₂ H o_0.5 C a_0.5 C u₃ O₈ Single Crystals: The Effect of Contamination from the Crucible on T _c

Single crystals of Pb₂Sr₂Ho_0.5Ca_0.5Cu₃O₈ have been grown in Pt, Al₂O₃ and Au crucibles by means of the flux method. The effect of contamination from the crucible on T_c has been investigated by studing the effects of Cu-site substitution on T_c and magnetic properties for sintered polycrystals of Pb₂Sr₂R_0.5Ca_0.5(Cu_{1- y} M _y)₃O₈ with R= Ho or Y and M= Pt or Al. Consequently it has been found that use of a Pt crucible leads to growth of single crystals of the best quality with high T _c values and that Al₂O₃ and Au crucibles contaminate the single crystals to decrease T _c. Anisotropy in the electrical resistivity of the single-crystal Pb₂Sr₂Ho_0.5Ca_0.5Cu₃O₈ has been found to be comparable to that of YBa₂Cu₃O₇ in spite of its thick blocking layer suggesting that the wave functions of conduction electrons moderately overlap along the c-axis in Pb₂Sr₂Ho_0.5Ca_0.5Cu₃O₈.