$\mathrm{Pb}({\mathrm{Zn}}_{1/3}{\mathrm{Nb}}_{2/3}){\mathrm{O}}_3\mathrm{\text{−}}x{\mathrm{PbTiO}}_3$ ($x=4.5\%–12\%$) relaxor ferroelectric crystals have been studied by means of acoustic emission (AE) in the 400–540 K temperature range. An anomalous AE activity independent of the ground state relaxor/morphotropic/ferroelectric crossover has been revealed at around 500 K, and it is associated with the “waterfall” feature related to the existence of polar nanoregions (PNRs). The 500 K AE anomaly is attributed to local martensitelike cubic-to-tetragonal ferroelectric transitions within the PNRs imbedded in a nonpolar (cubic) matrix.

• Received 5 March 2007

DOI:https://doi.org/10.1103/PhysRevLett.98.265701