Possible charge inhomogeneities in the CuO 2 planes of YBa 2 Cu 3 O 6+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 ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{6+x}$ $(x=0.25, 0.45, 0.65, 0.94)$ at 15 K have been measured by means of pulsed neutron diffraction. The PDF is modeled using a full-profile fitting approach to yield structural parameters. In contrast to earlier x-ray absorption fine structure 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 c direction. This is interpreted in terms of charge inhomogeneities in the ${\mathrm{CuO}}_{2}$ planes.