Elastic softening and polarization memory in PZN-PT relaxor ferroelectrics

Substantial elastic softening in the cubic phase of PZN-PT relaxor ferroelectric crystals is observed as a large hysteresis between the RUS frequencies from poled and depoled crystals. This is due to static switchable polar nanoregions (PNR) at $T$*, well below the conventional Burns temperature but ∼50 K above the ferroelectric transition. Elastic softening due to polarization of the PNR shows polarization memory through two phase transitions and is greater than the softening associated with polarization of the ferroelectric phases. This emphasizes that PNR dominate the material properties at all temperatures below $T$*.

Figure 1

Lower frequency portion of RUS spectra during heating of the [001]c poled PZN-4.5%PT crystal offset in the $y$ axis (amplitude) proportional to temperature. The blue line follows the lowest frequency mode and red spectra mark long-range ferroelectric transitions.

Figure 2

Data for 1/2(C${}_{11}$−C${}_{12}$) from the lowest frequency resonance mode in Fig. 1 of the poled crystal during heating (+,▲) and the depoled crystal after heating to ∼550 K (×,□). $T$* (∼475 K) marks the onset of hysteresis in elastic properties. Precision is generally $+$/− a few percent for the elastic constants though data on cooling 450 → 300 K are less precise.

Figure 3

Piezoelastic softening due to poling shown as the difference Δ1/2(C${}_{11}$−C${}_{12}$) between poled and depoled states in Fig. 2. Stability ranges for the $r$, $t$, and $c$ phases are shown.