Structure and physical properties of iron-selenide KxFe2-ySe2

We have synthesized the superconducting KxFe2-ySe2 (x = 0.8) crystal by using the one step technique. SEM images demonstrate terrace-like structures on the surface and the sample contains two phases. XRD pattern gives the (00l) peaks. The main peaks are indexed to the I4/m space group and the lattice parameter c is calculated to be 13.94076 angstrom. ZFC magnetization measurement exhibits a very sharp transition which indicates the presence of superconductivity in the crystal. The superconducting transition temperature, T-c(mag), obtained from magnetization measurement is estimated to be 31 K. The critical current value, Jc(0), deduced from the M-H loops for sample is approximately 9 x 10(4) A/cm(2) at 5 K. From magnetoresistivity measurement the T-c, T-c(onset) and T-c(offset) temperatures at the absence of the external magnetic field are found as 32.2, 33.1 K and 31.5 K, respectively. The calculated flux pinning or activation energy U is around 0.46 eV for 0 T. (C) 2015 Elsevier B.V. All rights reserved.