a Department of Chemistry, Moscow State University, 119899, Moscow, Russia
b EMAT, University of Antwerp (RUCA), Groenenborgerlaan 171, B-2020, Antwerp, Belgium
Abstract:
Bulk superconductivity with Tc up to 94 K has been induced by fluorination of non-superconducting YBa2Cu3O6.11 using XeF2 as a fluorination agent. Strong changes on X-ray patterns were found after fluorination of reduced YBCO. High resolution electron microscopy of superconducting samples showed the presence of a new phase with c ≈ 13 Å which exists as noticeable areas included within a matrix of the 123 structure or which occurs as isolated defects with a limited extension. All fluorinated compounds exhibited a strong disorder along the c-direction resulting in a ‘loss’ of c-parameter on X-ray patterns. The present results demonstrate that fluorine indeed enters the YBCO structure with a significant structural rearrangement for the high level of fluorination. The structure of the fully fluorinated YBa2Cu3O6F2 phase, possibly responsible for superconductivity, has been deduced from high resolution electron microscopy.