  We discuss the static deformations of the doped CuO_2 lattices in
YBa_2Cu_3O_x. Intrinsic lattice effects driven by the strong correlations of
the electron system are separated from extrinsic chemical and bandstructure
effects. c-axis displacements of the planar copper atoms seem to be a generic
property of the metallic CuO_2 lattices.
