Substitution effects of Ag into FeSe0.5Te0.5 superconductor

Ag added bulk FeSe0.5Te0.5 samples Ag-x(FeSe0.5Te0.5)(1-x) were prepared by solid-state reaction. The x, nominal concentration of Ag, was ranged between 0 and 0.08. The mixed powder was first put into an alumina tube and sealed in an evacuated quartz tube that was heated at 1323 K for 20 h. Subsequently, it was cooled to 673 K and annealed for 200 h to stabilize the superconductive layers. The pure Ag or Ag compound was not observed in the X-ray diffraction patterns of Ag doped samples. It indicates that the Ag is doped into the lattice site of FeSe0.5Te0.5. The T-c is about 14 K up to x = 0.04, but the T-c decreases gradually to 11 K above x = 0.05. The magnetization decreased with increase of x, but a fishtail-like hump was observed for x = 0.05 sample. The magnetic hysteresis of x = 0.05 sample is larger than that of x = 0 sample above 2T. (C) 2012 Elsevier B. V. All rights reserved.