The structure of fluorinated YBa2Cu3O6Fx phases has been determined us
ing a combination of X-ray diffraction, electron diffraction, high-res
olution electron microscopy and microanalysis. It was unambiguously de
monstrated that fluorine indeed enters the structure at the oxygen pos
itions of the Cu(1) plane. The structure of the fully fluorinated phas
e YBa2Cu3O6F2 is mainly deduced from high-resolution electron microsco
py.