Fluorination of YBa2Cu3O7−x

We have developed a simple gas-exchange technique for the introduction of fluorine into the structure of YBa2Cu3O7−x. Th e presence of fluorine in the resulting compounds has been determined by observation of systematic variation of the unit cell with exposure to fluorine. It has been further confirmed by NMR and neutron diffraction experiments, the details of which are to be presented elsewhere. The desired fluorination reaction always occurs in competition with decomposition processes, which eventually produce the fluorides of the component metals. This effect was minimized by use of a thoroughly dried reactant gas and a moderate temperature (165°C). Fluorine enters the tetragonal YBa2Cu3O6 structure quite readily. It appears to have much more difficulty entering the more oxidized, orthorhombic form. This we attribute to the blocking of potential migration paths in the structure by oxygen.