Materials Characterization

Phonon localization drives nanoregions in a relaxor ferroelectric

This inelastic neutron scattering spectrum shows the localizing modes (LMs) between the transverse optic (TO) and transverse acoustic (TA) phonons at a temperature near the stability limit of the polar nanoregions (Burns temperature).

Neutron scattering measurements reveal that phonon localization drives the generation of polar nanoregions (PNRs) in a relaxor ferroelectric. PNRs facilitate the ability of relaxor ferroelectrics to convert between electrical and mechanical forms of energy, which is used in applications ranging from medical ultrasound to military sonar devices.

Relaxor ferroelectrics belong to a larger class of functional materials where disorder “frustrates” the active phase transition, resulting in the formation of inhomogeneous nanoregions and frequency dependent relaxation behavior. Despite 30 years of intense research on PNRs, however, there has been no agreement on their origin. Our results reveal that PNRs originate with nanoregions of standing polar phonons that form at temperatures hundreds of degrees above the stability range of the PNRs. Anderson-localization of the phonons by resonance modes explains the observations and, with nonlinear slowing, the PNRs and relaxor behavior. Results also show that the size and shape of PNRs are not controlled by structure, as always assumed, but by phonon resonance wavevectors. This finding could help steer the design of future-generation relaxor ferroelectrics for a wide range of applications.

M. E. Manley, J. W. Lynn, D. L. Abernathy, E. D. Specht, O. Delaire, A. R. Bishop, R. Sahul,  and J. D. Budai, “Phonon localization drives polar nanoregions in a relaxor ferroelectric,” Nature Commun. 5:3683 doi: 10.1038/ncomms4683 (2014).

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