The polarization noise of small samples of the relaxor ferroelectric ${\mathrm{Pb}}_{1-x}{\mathrm{La}}_x{\mathrm{Zr}}_{1-y}{\mathrm{Ti}}_y{\mathrm{O}}_3$ was studied both in thermal quasiequilibrium and while the applied field was swept. The quasiequilibrium noise obeyed the fluctuation-dissipation relation. This noise was Gaussian and lacked random features, within experimental resolution. No Barkhausen noise was detected during field sweeps at near-saturating fields. Both those facts point to small coherence volumes for the polarization dynamics.

• Received 6 June 1997

DOI:https://doi.org/10.1103/PhysRevB.56.R11365