  We have performed a series of neutron diffuse scattering measurements on a
single crystal of the solid solution Pb(Zn$_{1/3}$Nb$_{2/3}$)O$_3$ (PZN) doped
with 8% PbTiO$_3$ (PT), a relaxor compound with a Curie temperature T$_C \sim
450$ K, in an effort to study the change in local polar orders from the polar
nanoregions (PNR) when the material enters the ferroelectric phase. The diffuse
scattering intensity increases monotonically upon cooling in zero field, while
the rate of increase varies dramatically around different Bragg peaks. These
results can be explained by assuming that corresponding changes occur in the
ratio of the optic and acoustic components of the atomic displacements within
the PNR. Cooling in the presence of a modest electric field $\vec{E}$ oriented
along the [111] direction alters the shape of diffuse scattering in reciprocal
space, but does not eliminate the scattering as would be expected in the case
of a classic ferroelectric material. This suggests that a field-induced
redistribution of the PNR has taken place.
