Phonon localization drives polar nanoregions in a relaxor ferroelectric

Abstract

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.

Fano resonance and dipolar relaxation in lead-free relaxors

“…It is expected that the presently discovered Fano resonance may also occur in other solid solutions whose relaxor properties arise from such difference in off-centering between their alloyed elements. Note, however, that lead-based relaxors (for example, the Pb(Mg 1/3 Nb 2/3 )O 3 -based systems), which are likely more complicated than lead-free relaxors, may need to invoke rather complex phenomena to reproduce their properties 64 . Our simulations also predict a thermally activated THz relaxation mode, which is in agreement with the previous experiment 28 .…”

Optical evidences for an intermediate phase in relaxor ferroelectric Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 single crystals

“…At the frequency of a preexisting resonance mode, nanoregions of ferroelectric phonons develop with a coherence length equal to one wavelength and the size of nanostructure. 22 The PNRs can be used to represent dynamical polarization fluctuations (with a finite lifetime shorter than the average acoustic phonon period), which are not associated with an elastic quadrupole moment or local strain field because of the finite lifetime. 21 When the temperature decreases and correlations become stronger, the lifetime increases and local strain fields can eventually develop, stabilizing the PNRs into permanently distorted PNDs.…”

“…24 It means that PNRs could be described in terms of transverse-wavelike distortions, whose sizes and shapes can be dictated by phonon resonance wave vectors. 22 The softening of TO phonon can be clearly detected with increasing temperature from Raman spectra, which is a convenient probe for local or microscopic changes in dynamics. With further increasing temperature, the vanishing of TO phonon indicates not only a phase transition from short-range Mc to T structure but also the existence of PNCs.…”

“…The localization of phonons was found to drive PNRs in relaxors using neutron scattering. 22 A local enhancement of the nonlinearity associated with off-centring Pb atoms instigates the formation of ILMs on cooling. 28 Then, the frequency of ILMs slows below that of the TO phonon into the frequency gap between the TA and TO phonons, and eventually vanishes as PNRs become static, as shown in Fig.…”

Development of Data Acquisition and Measurement Software for Neutron Triple Axis Spectrometer at BATAN-Serpong, Indonesia

“…The neutron triple-axis spectrometer (TAS) can measure the momentum and energy changes of neutrons after interaction with a material, so the material characteristics related to its dynamics can be determined [8]. The TAS of the National Nuclear Energy Agency of Indonesia (BATAN) was constructed for research of inelastic scattering from condensed matter and investigation of collective excitations from the lattice (phonons) or from magnetically ordered system (magnons) [9][10][11][12]. However, in 1996-2005, the spectrometer was not able to run experiments since there was a malfunction of the main computer for data acquisition and control.…”