title: Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations.
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.
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Michael E
authors.identifier: 0000-0003-4053-9986
authors.initials: ME
authors.lastname: Manley
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Douglas L
authors.identifier: 0000-0002-3533-003X
authors.initials: DL
authors.lastname: Abernathy
authors.affiliation: TRS Technologies, State College, PA 16801, USA.
authors.forename: Raffi
authors.initials: R
authors.lastname: Sahul
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, USA.
authors.forename: Daniel E
authors.initials: DE
authors.lastname: Parshall
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology (NIST), Gaithersburg, MD 20899, USA.
authors.forename: Jeffrey W
authors.identifier: 0000-0003-3626-4932
authors.initials: JW
authors.lastname: Lynn
authors.affiliation: Quantum Condensed Matter Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Christianson
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Paul J
authors.identifier: 0000-0002-6846-2442
authors.initials: PJ
authors.lastname: Stonaha
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Eliot D
authors.identifier: 0000-0002-3191-2163
authors.initials: ED
authors.lastname: Specht
authors.affiliation: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: John D
authors.identifier: 0000-0002-7444-1306
authors.initials: JD
authors.lastname: Budai
mesh_terms: D017097:Electric Impedance; D004560:Electricity; D059346:Magnets / Q000737:chemistry*; D055595:Mechanical Phenomena; D018625:Microscopy, Atomic Force; D049329:Nanostructures / Q000737:chemistry*; D033363:Neutron Diffraction; D060739:Phonons; D014025:Titanium / Q000737:chemistry; D014732:Vibration
chemical_list: D014025:Titanium
keywords: Piezoelectricity; ferroelectric; local modes; neutron scattering; phonons; relaxor