Inelastic neutron scattering investigation of external modes in incommensurate and commensurate A<sub>2</sub>BX<sub>4</sub>materials

Etxebarria, I.; Quilichini, M.; Perez-Mato, J. M.; Boutrouille, P.; Zúñiga, F. J.; Bréczewski, T.

doi:10.1088/0953-8984/4/44/016

Cited by 23 publications

(18 citation statements)

References 33 publications

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“…18, Γ AO (q) = 0 will assumed in the following. The wave vector dependence of dynamical matrix D q can be conveniently cast in the form which appears in the simplest nearest-neighbor interaction models with two degrees of freedom per unit cell 23,24,25 :…”

Section: 19mentioning

confidence: 99%

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

et al. 2003

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We have undertaken an inelastic neutron scattering study of the perovskite relaxor ferroelectric Pb(Zn 1/3 Nb 2/3 )O3 with 8% PbTiO3 (PZN-8%PT) in order to elucidate the origin of the previously reported unusual kink on the low frequency transverse phonon dispersion curve (known as "waterfall" effect). We show that its position (q wf ) depends on the choice of the Brillouin zone and that the relation of q wf to the size of the polar nanoregions is highly improbable. The waterfall phenomenon is explained in the framework of a simple model of coupled damped harmonic oscillators representing the acoustic and optic phonon branches.

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Section: 19mentioning

confidence: 99%

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

et al. 2003

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“…Soft phonon branches are known e.g. from incommensurate dielectrics [33,34]. As a matter of fact, soft polarization branches ensure a simultaneous instability with respect to both the homogeneous and the staggered polarization, and this seems to be the essential prerequisite of an AF material [35,36].…”

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confidence: 99%

Multiple Soft-Mode Vibrations of Lead Zirconate

et al. 2014

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Polarized Raman, IR and time-domain THz spectroscopy of orthorhombic lead zirconate single crystals yielded a comprehensive picture of temperature-dependent quasiharmonic frequencies of its low-frequency phonon modes. It is argued that these modes primarily involve vibration of Pb and/or oxygen octahedra librations and their relation to particular phonon modes of the parent cubic phase is proposed. Counts of the observed IR and Raman active modes belonging to distinct irreducible representations agree quite well with group-theory predictions. The most remarkable finding is the considerably enhanced frequency renormalization of the y-polarized polar modes, resulting in a pronounced low temperature dielectric anisotropy. Results are discussed in terms of contemporary phenomenological theory of antiferroelectricity.PACS numbers: 77.80.Bh, 77.84.Cg Although the ferroelectric and antiferroelectric materials have a lot in common, the latter have been much less investigated. An obvious reason is the absence of the direct linear coupling of the antiferroelectric (AF) order parameter to the macroscopic electric field.At the same time, a nonlinear coupling to the macroscopic electric field is still present. Therefore, AF materials actually do provide interesting functionalities, as well. In fact, the AF oxides are promising materials for high-energy storage capacitors, high-strain actuators and perhaps even for electrocaloric refrigerators [1][2][3]. The interest in the improvement of our understanding of AF oxides has been expressed recently [1,2,4,5].Lead zirconate, PbZrO 3 , is the best known example of an AF oxide -it is an end-member of technologically relevant solid solutions with PbTiO 3 (piezoelectric PZTs) [1,2,4,[6][7][8]. The parent paraelectric phase is a simple cubic perovskite with a 5-atom unit cell (P m3m, Z=1). Below the AF phase transition (T C ∼ 500 K), it goes over into an orthorhombic P bam (Z=8) structure [10,11]. The space-group symmetry change can be well understood[1] as a result of the condensation of two order parameters [1,4,9,12]. One of them is a polarization wave of a propagation vector Q Σ = (0.25, 0.25, 0) pc , the other order parameter is a Q R = (0.5, 0.5, 0.5) pc oxygen octahedra tilt mode (here pc stands for pseudocubic lattice, see Figs. 1-2).Superpositions of Q Σ , Q R include also Γ, X, M and Q S = (0.25, 0.25, 0.5) pc cubic-phase Brillouin zone points. All of these points become Brillouin zone centers in the P bam phase (see Fig. 2). Nevertheless, recent inelastic X-ray scattering experiments [4] have clearly demonstrated that the critical scattering occurs only in the vicinity of the Γ-point. Based on this experimental result, it was proposed that the AF phase transition is driven by a single mode, the Γ-point ferroelectric soft mode [4]. Within this model, the condensation of the Q Σ -point mode can be ascribed to the flexoelectric coupling with the ferroelectric mode, and the condensation of the Q R -point mode can be explained as due to a biquadratic coupling with the Q Σ m...

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“…The renormalization of the coupling constants s a , s c , s a and s c , describing the translation-rotation coupling, may in principle contribute to the soft-mode renormalization as was recently proposed in the case of K 2 SeO 4 [25]. However, the temperature derivative of the ω 2 B 2u (L) frequency, which does not depend on the parameters s i and t i at all, is even higher than that of the soft mode itself.…”

Section: The Essential Soft Quasi-harmonic Parametermentioning

confidence: 93%

“…This is justified for most insulators, because the limitation of the Fourier development of the bare mode dispersion to the first few terms corresponds physically to the approximation of short-range interactions. A simple mode-mixing model of this type was recently proposed by Pérez-Mato [25] for K 2 SeO 4 .…”

Section: Introductionmentioning

confidence: 99%

Specialised acousto-optical processor for input, display, and coherent-optical processing of multiparameter information from spaceborne telemetric systems

Bykovskii¹,

Eloev²,

Kukharenko³

et al. 1995

Quantum Electron.

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A ten-parameter quasi-harmonic semimicroscopic model for the low-frequency lattice dynamics of betaine calcium chloride dihydrate is presented. The choice of the relevant variables and interaction terms of the model potential is mainly based on the known crystallographic data, while the values of the quasi-harmonic force constant parameters are adjusted to our recent inelastic neutron scattering data. The parameter with the largest temperature derivative is determined and the origin of its temperature renormalization is discussed.

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Inelastic neutron scattering investigation of external modes in incommensurate and commensurate A₂BX₄materials

Cited by 23 publications

References 33 publications

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

Multiple Soft-Mode Vibrations of Lead Zirconate

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Inelastic neutron scattering investigation of external modes in incommensurate and commensurate A2BX4materials

Cited by 23 publications

References 33 publications

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

Origin of the “Waterfall” Effect in Phonon Dispersion of Relaxor Perovskites

Multiple Soft-Mode Vibrations of Lead Zirconate

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Inelastic neutron scattering investigation of external modes in incommensurate and commensurate A₂BX₄materials