  X-ray and neutron scattering studies of the lead-based family of perovskite
relaxors PZN-$x$PT and PMN-$x$PT have documented a highly unusual situation in
which the near-surface region of a single crystal can exhibit a structure that
is different from that of the bulk when cooled to low temperatures. The
near-surface region, or "skin" can also display critical behavior that is
absent in the crystal interior, as well as a significantly different lattice
spacing. By varying the incident photon energy, and thus the effective
penetration depth, x-ray measurements indicate a skin thickness of order 10
$\mu$m to 50 $\mu$m for PZN-$x$PT samples with $0 \le x \le 8$%. Neutron
residual stress measurements on a large PMN single crystal reveal a uniform
lattice spacing within the bulk, but an increased strain near the surface. The
presence of this skin effect has led to incorrect phase diagrams for both the
PZN-$x$PT and PMN-$x$PT systems and erroneous characterizations of the nature
of the relaxor state.
