Speaker
Description
Relaxor ferroelectrics exhibit broad, diffuse phase transitions, and polar nanoregions (PNRs) in place of the long-range ordering observed in displacive ferroelectrics. While displacive ferroelectrics are explained by the well established soft-phonon theory, a corresponding intrinsic-localized-mode (ILM) theory for relaxors—first introduced by Bussmann-Holder et al. in 2005—has remained elusive experimentally. The challenge largely stems from a “waterfall” effect that obscures the ILM spectral region. In this talk, neutron scattering will be presented on the lead-free uniaxial relaxor ferroelectric strontium barium niobate to reveal evidence of ILMs that form PNRs. In this system the transverse optic (TO) phonon is observed without the waterfall effect, unveiling flat ILM bands below the TO phonon that become increasingly intense upon cooling toward the phase transition and ultimately condense into diffuse elastic scattering associated with PNR formation. Analysis of the ILM intensities supports the idea that they act as a local order parameter for the diffuse relaxor phase transition.