  Relaxor ferroelectrics are complex materials with distinct properties
different from classic ferroelectrics. Probing frequency depended dielectric
susceptibility is its trait. Other empirical laws build on classic
ferroelectrics are still applicable to relaxor ferroelectrics. Here we report
an abnormal improved dielectric in La doped relaxor ferroelectric
0.4PNN-0.6PHT, which deviated from the consistent variation relationship with
piezoelectric coefficient. A mesoscale mechanism is proposed to reveal the
origin of the improved dielectric response in 0.4PNN-0.6PHT, where the polar
nanoregions alignment can facilitate polarization response to external field.
This mechanism emphasizes the critical role of polarization fluctuation on the
macroscopic properties of 0.4PNN-0.6PHT.
