Location of fluorine atoms and mechanism of improving superconducting properties with F-doped in YBaCuO series

摘要

A series of YBa_2Cu_3O_6.5-0.5x+δFx(x = 0, 0.3, 0.6, 1.0, 1.5, 2.0) samples were synthesized using state reaction method. The superconducting properties and microstructures of the samples were studied with AC susceptibility, DC resistivity, fluorine and oxygen content measurements, XRD, IR and XPS techniques. The results show that F-dop- ing increases the Tc and decreases the transition width, and fluorine atoms have entered into the superconducting phase and substituted for the oxygen atoms at O(4) sites. The mechanism of improving superconducting properties is that fluo- rine-doping adjusts the hole carrier concentration in the Cu-O glanes.