Possible charge inhomogeneities in the CuO2 planes of YBa2Cu3O6+x (x=0.25, 0.45, 0.65, 0.94) from pulsed neutron diffraction

The atomic pair distribution functions (PDF) of four powder samples of YBa2Cu3O6+x (x=0.25, 0.45, 0.65, 0.94) at 15 K have been measured by means of pulsed neutron diffraction. The PDF is modelled using a full-profile fitting approach to yield structural parameters. In contrast to earlier XAFS work we find no evidence of a split apical oxygen site. However, a slightly improved fit over the average crystallographic model results when the planar Cu(2) site is split along the z-direction. This is interpreted in terms of charge inhomogeneities in the CuO2 planes.