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Sci Adv. 2016 Sep 16;2(9):e1501814. doi: 10.1126/sciadv.1501814. eCollection 2016 Sep.

Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations.

Author information

1
Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
2
Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
3
TRS Technologies, State College, PA 16801, USA.
4
NIST Center for Neutron Research, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, USA.

Abstract

Relaxor-based ferroelectrics are prized for their giant electromechanical coupling and have revolutionized sensor and ultrasound applications. A long-standing challenge for piezoelectric materials has been to understand how these ultrahigh electromechanical responses occur when the polar atomic displacements underlying the response are partially broken into polar nanoregions (PNRs) in relaxor-based ferroelectrics. Given the complex inhomogeneous nanostructure of these materials, it has generally been assumed that this enhanced response must involve complicated interactions. By using neutron scattering measurements of lattice dynamics and local structure, we show that the vibrational modes of the PNRs enable giant coupling by softening the underlying macrodomain polarization rotations in relaxor-based ferroelectric PMN-xPT {(1 - x)[Pb(Mg1/3Nb2/3)O3] - xPbTiO3} (x = 30%). The mechanism involves the collective motion of the PNRs with transverse acoustic phonons and results in two hybrid modes, one softer and one stiffer than the bare acoustic phonon. The softer mode is the origin of macroscopic shear softening. Furthermore, a PNR mode and a component of the local structure align in an electric field; this further enhances shear softening, revealing a way to tune the ultrahigh piezoelectric response by engineering elastic shear softening.

KEYWORDS:

Piezoelectricity; ferroelectric; local modes; neutron scattering; phonons; relaxor

PMID:
27652338
PMCID:
PMC5026422
DOI:
10.1126/sciadv.1501814
[Indexed for MEDLINE]
Free PMC Article

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