Soft Phonon Modes and Diffuse Scattering in Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 Relaxor Ferroelectrics

TL;DR

This study investigates the phonon behavior and diffuse scattering in a specific relaxor ferroelectric crystal, revealing PNR dynamics, phonon coupling, and the waterfall phenomenon, advancing understanding of relaxor ferroelectric mechanisms.

Contribution

It provides detailed neutron scattering analysis of PNRs, phonon coupling, and polarization effects in a ternary relaxor ferroelectric, highlighting anisotropic interactions and temperature-dependent phonon modes.

Findings

PNRs emerge at 630 K and grow upon cooling.

Diffuse scattering patterns are asymmetric under electrical poling.

Confirmation of PNR-acoustic phonon coupling and the waterfall phenomenon.

Abstract

Single crystals of a ternary relaxor ferroelectric system, 0.29Pb(In1/2Nb1/2)O3-0.45Pb(Mg1/3Nb2/3)O3-0.26PbTiO3, have been studied using triple-axis based elastic and inelastic neutron scattering. Elastic diffuse scattering confirms the presence of polar nano-regions (PNRs) in this system. The PNRs emerge at the Burns temperature, TB = 630 K and then grow continuously in population and correlation size as the crystal cools down to 100 K. At 300 K, characteristic 'butterfly' and ellipsoid shaped diffuse scattering patterns are observed on the HK0 reciprocal space plane. Electrical poling along the [110] direction produces a marked asymmetry in the diffuse scattering patterns, with the parallel-to-the-field components enhanced while the perpendicular-to-the-field components suppressed. Several low energy phonon branches along the [001] and [111] directions were studied. Most significantly, the PNR-acoustic phonon coupling is confirmed for the [110] transverse acoustic (TA) phonons polarized along the [1-10] real space direction and the [100] TA phonons. This coupling appears to be anisotropic and correlated with the distribution of PNRs, and also affected by the relative length scales of the PNRs and phonon wave vectors. The well-known 'waterfall' phenomenon is observed on the [001] and [110] transverse optical (TO) branches, near the zone center. The optical phonon measurements also reveal a lowest-energy, zone center soft TO mode, whose squared phonon energy increase linearly with decreasing temperature below the TB.