  Large low-frequency noise is found in some perovskite relaxor ferreoelectrics
when they are polarized, regardless of whether the polarization is accompanied
by an applied electric field. The noise appears both in the ferroelectric and
relaxor states, including in the nominally ergodic paraelectric state at
temperatures above the susceptibility peak. Since it is present whenever the
samples are microphonic due to piezoelectricity but not evident when they are
not microphonic, it appears to be a response to mechanical strain changes.
Dependence of the noise on sample thermal history indicates that
non-equilibrium strain relaxation is the source, even in the temperature range
for which the sample is nominally ergodic. Non-equilibrium noise in the absence
of net piezoelectricity is found at somewhat higher frequencies.
