Structural and physical properties of Na-substituted K0.8Fe2-ySe2 single crystal

In this study, the superconducting NaxK1-xFe2-ySe2 (x = 0.16) crystals via the self-flux technique were produced. A successive plate-like surfaces aligned in ab-plane were observed from SEM images. A set of 001 reflections, typical for ferroselenides of alkali metals which apparently correspond to the main 245 phase, is observed on XRD single crystal pattern. Magnetization against temperature measurement in ZFC mode shows a significant transition at around 31 K. It should be emphasized that we have observed the stable superconducting phase in the system for over two years, in the medium where H2O-O-2 content is less than 0.1 ppm. However the superconducting phase in the system is quite non-durable in the atmospheric air. From magneto-resistance measurements, it is observed that Na0.16K0.64Fe2-ySe2 system shows very weak TAFF behavior in the applied field of 7 T, suggesting the existence of strong pinning force in the system. The critical current density, J(c)(0), calculated from the hysteresis loops are found as 6.7 x 10(4) A/cm(2) at 5 K. H-irr is estimated to be 10.70, 14.48, and 9.78 Tat the temperatures of 5, 10, and 20 K, respectively. (C) 2018 Elsevier B.V. All rights reserved.