Vortex phase transition and anisotropy behavior of optimized (Li1-xFexOH) FeSe single crystals

(Li1-xFexOH)FeSe single crystals have been successfully synthesized by a hydrothermal ion-exchange technique. We have carried out systematic research on the influence of the concentration of selenourea (c(m)) on the superconducting properties of (Li1-xFexOH)FeSe single crystals. The optimized specimens possess an onset superconducting transition temperature T-c of up to 42 K obtained at c(m) = 0.8 mol l(-1), and the corresponding residual resistivity ratio (RRR = rho (300 K)/rho(T-c)) is estimated to be 11. The vortex liquid-to-glass phase transition has been discussed based on the collective pinning model. The large distance between the H-g and H-c2 lines, as well as the much narrower region of the pinned vortex-liquid phase, indicate a weak vortex-pinning ability in (Li1-xFexOH)FeSe single crystals. The big out-plane anisotropy behavior versus temperature has been explored according to the anisotropic Ginzburg-Landau theory, and the anisotropy factor G displays linear behavior towards temperature similar to that of SmFeAsO1-xFx superconductors.