Local structural evidence for charge inhomogeneities in the CuO2 planes ofYBa2Cu3O6+x x=0.25, 0.45, 0.65, 0.94

The atomic pair distribution function (PDF) of YBa2Cu3O6+x (x=0.25, 0.45, 0 .65, 0.94) at 15 K has been measured. From least-squares full-profile model ing no split position is found for the apical oxygen in contrast to earlier XAFS work. Instead, an improvement over the average crystallographic struc ture results for a split planar Cu(2) site. This finding supports the exist ence of charge inhomogeneities throughout the planes and may resolve a long -standing controversy between the XAFS and diffraction community.