2016/08/04 by J. Toulouse, E. M. Iolin, E. Iolin +4 · 2 citations
Engineering · Materials Science · Physics and Astronomy · #Acoustic Wave Resonator Technologies #Atomic physics #Brillouin zone #Center (category theory) #Condensed matter physics #Crystallography #Ferroelectric and Piezoelectric Materials #Omega #Optics #Phonon #Physics #Quantum mechanics #Resonance (particle physics) #Scattering #Solid-state spectroscopy and crystallography #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physrevb.94.214116
published in Physical review. B./Physical review. B 94(21) (American Physical Society)
arxiv created 2016/08/04 · openalex created_date 2016/08/23 · openalex publication_date 2016/12/30 · arxiv updated 2017/01/04 · openalex updated_date 2026/08/05
The damping (\mathrm\ensuremathΓa) of the transverse acoustic (TA) phonon in single crystals of the relaxor KTa_1\ensuremath-xNbxO3 with x=0.15--0.17 was studied by means of high resolution inelastic cold neutron scattering near the (200) Brillouin Zone (BZ) point where diffuse scattering is absent, although it is present near (110). In a wide range of temperatures centered on the phase transition, T=195\phantom\rule0.16em0exK\textdiv108\phantom\rule0.16em0exK, the TA phonon width (damping) exhibits a step increase around momentum q=0.07, goes through a shallow maximum at q=0.09--0.12, and remains high above and up to the highest momentum studied of q=0.16. These experimental results are explained in terms of a resonant interaction between the TA phonon and the collective or correlated reorientation through tunneling of the off-center Nb+5 ions. The observed TA damping is successfully reproduced in a simple model that includes an interaction between the TA phonon and a dispersionless localized mode (LM) with frequency \ensuremathωL and damping \mathrm\ensuremathΓL(\mathrm\ensuremathΓL<\ensuremathωL), itself coupled to the transverse optic (TO) mode. Maximum damping of the TA phonon occurs when its frequency is \ensuremathωa\ensuremath≈\ensuremathωL. The values of \ensuremathωL and \mathrm\ensuremathΓL are moderately dependent on temperature, but the oscillator strength, M2, of the resonant damping exhibits a strong maximum in the range T\ensuremath∼120\phantom\rule0.16em0exK\textdiv150\phantom\rule0.16em0exK in which neutron diffuse scattering near the (110) BZ point is also maximum and the dielectric susceptibility exhibits the relaxor behavior. The maximum value of M appears to be due to the increasing number of polar nanodomains. In support of the proposed model, the observed value of \ensuremathωL\ensuremath≈0.7\phantom\rule0.16em0exTHz is found to be similar to the estimate previously obtained by Girshberg and Yacoby [J. Phys.: Condens. Matter 24, 015901 (2012)]. Alternatively, the TA phonon damping can be successfully fitted in the framework of an empirical Havriliak-Negami (HN) relaxation model that includes a strong resonancelike transient contribution.