The effects of sulphur substitution on Y(Ba,Sr)2Cu2.5B0.5Oz systems

Abstract A series of doped compounds Y(Ba,Sr) 2 Cu 2.5 B 0.5− x S x O z (0 ⩽ × ⩽ 0.5) were synthesized by the solid state reaction method. The effects of sulphur doping on crystal structure as well as superconductivity in these samples were studied. An interesting phenomenon can be observed that superconductivity is destroyed at low doping level of sulphur (× ⩽ 0.2) and is induced again as doping level of sulphur increases ( x ⩾ 0.3) in the YBaSrCu 2.5 B 0.5− x S x O z (0 ⩽ × ⩽ 0.5) series. An initial explanation related to the large difference between B 3+ and S 6+ was made to interpret this experimental fact. The possibility of inducing extra hole concentration by substituting [BO 3 ] 3− with [SO 4 ] 2− groups and thus improving superconductivity was also discussed. These result may give new evidence for doping mechanism of substitution among oxyanion groups.