Superconductivity and critical fields in undoped and Sn-doped MoSr2YCu2O8−δ

Samples with nominal compositions MoSnxSr2YCu2O8−δ (0 ⩽ x ⩽ 0.075) were synthesized and their superconducting and magnetotransport properties were investigated. It was established that the optimum Sn-doping (x = 0.02 and 0.03) increases the Tc of the undoped MoSr2YCu2O8−δ. The upper critical fields of the samples were determined using magnetization, susceptibility and resistivity measurements. It was established that the Sn-doping weakly affects the first and the intragrain second critical field of Mo-1212 but enhances the extrapolated to T = 0 (i.e. the intergrain) upper critical field. The observed phenomena were discussed on the basis of the Josephson-junction-arrays model. A phenomenological expression describing the temperature dependency of the susceptibility of Mo-1212 was found.