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 (PDFs) of four powder samples of YBa 2Cu3O6+x (x = 0.25, 0.45, 0.65, 0.94) at 15 K have been measured by means o f pulsed neutron diffraction. The PDF is modeled using a full-profile fitti ng approach to yield structural parameters. In contrast to earlier x-ray ab sorption fine structure work we find no evidence of a split apical oxygen s ite. However, a slightly improved fit over the average crystallographic mod el results when the planar Cu(2) site is split along the c direction. This is interpreted in terms of charge inhomogeneities in the CuO2 planes.