Effect of fluorination on the structure and superconducting properties of Y2Ba4Cu7O14+δ phases

Abstract Strongly reduced Y 2 Ba 4 Cu 7 O 14.09 has been successfully fluorinated using XeF 2 as a fluorination agent. The structure of the fluorinated material has been studied by a combination of X-ray diffraction, electron diffraction, high resolution electron microscopy (HREM) and X-ray microanalysis (EDX). For a high level of fluorination, the intercalation of fluorine is accompanied by a significant structural rearrangement and leads to an increase of T c from 30 to 62 K. HREM reveals the presence of a partially fluorinated, well ordered Y 2 Ba 4 Cu 7 O 14 F δ phase with c =51.96 A. Fluorine enters into anion-deficient Cu1 layers, resulting in the formation of an octahedral arrangement of part of the Cu1 atoms with a significant elongation of the apical Cu–O distances and the c -parameter. Local ordering of fluorine atoms leads to the formation of defects with a limited extension where all Cu1 atoms have an octahedral coordination; the c -parameter in these areas is as high as 53.5 A.