Relaxor ferroelectrics exemplify a class of functional materials where interplay between disorder and phase instability results in inhomogeneous nanoregions. Although known for about 30 years, there is no definitive explanation for polar nanoregions (PNRs). Here we show that ferroelectric phonon localization drives PNRs in relaxor ferroelectric PMN-30%PT using neutron scattering. At the frequency of a preexisting resonance mode, nanoregions of standing ferroelectric phonons develop with a coherence length equal to one wavelength and the PNR size. Anderson localization of ferroelectric phonons by resonance modes explains our observations and, with nonlinear slowing, the PNRs and relaxor properties. Phonon localization at additional resonances near the zone edges explains competing antiferroelectric distortions known to occur at the zone edges. Our results indicate the size and shape of PNRs that are not dictated by complex structural details, as commonly assumed, but by phonon resonance wave vectors. This discovery could guide the design of next generation relaxor ferroelectrics.

Polar nanoregion vibrations control the ultrahigh piezoelectric response of relaxor-based ferroelectrics used in applications.

Piezoelectric materials lie at the heart of electromechanical devices. Applications include actuators, ultrasonic imaging, high intensity focused ultrasound, underwater ultrasound, nondestructive evaluation transducer, pressure sensors, and accelerometers, to name a few. In this work, the advantages and disadvantages of relaxor-PbTiO3-based single crystals are discussed, based on the requirements (figure of merit) of various applications, with emphasis on recent developments of the shear properties of single crystals as a function of temperature and applied fields.

The complete set of material constants of single domain rhombohedral phase 0.27Pb(In1/2Nb1/2)O3-0.46Pb(Mg1/3Nb2/3)O3-0.27PbTiO3:Mn single crystal has been determined. The orientation dependence of piezoelectric, dielectric, and electromechanical properties was calculated based on these single domain data. The maximum piezoelectric and electromechanical properties were found to exist near the [001]C pseudo-cubic direction. In addition, the piezoelectric properties of [001]C poled crystals with “4R” multi-domain configuration were experimentally measured and compared with the calculated values. Only a small difference (3%) was found between experimental and theoretical values, indicating the high piezoelectric properties in the “4R” state are mainly from intrinsic contributions. The mechanical quality factors Q33 are significantly improved by the Mn-doping for the “4R” domain engineered crystals but almost no change for the single domain “1R” state. On the other hand, Q15 of both single domain and multidomain crystals were found to increase with Mn-doping, due to the internal bias induced by acceptor dopants, which clamps the domain wall motions and restricts polarization rotation.