Soft vibrational mode in LiNbO3 and LiTaO3

Servoin, J. L.; Gervais, F.

doi:10.1016/0038-1098(79)90562-3

Cited by 56 publications

(25 citation statements)

References 11 publications

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“…At 633 K the static dielectric constant has increased further and the polariton frequency appears to saturate below 3 THz, which indi- cates the presence of a strong resonance near this frequency. A previous continuous-wave infrared reflectivity study also showed strong evidence for the rise of a strong resonance near 3 THz with increasing temperature (Servoin and Gervais, 1979).…”

Section: Resultsmentioning

confidence: 66%

“…A clear consequence of this strong coupling is that it is impossible to distinguish mode-softening effects from the rise of a relaxational response. Indeed, for LiTaO 3 and LiNbO 3 , a very complicated low-frequency dielectric response has been observed that shows both mode-softening and relaxational mode characteristics (Johnston and Kaminow, 1968;Chowdhurry et al, 1978;Servoin and Gervais, 1979;Okamoto et al, 1985, Zhang andScott, 1986). In addition to the direct and the relaxational dielectric response of the ferroelectric phonon, there can be a contribution due to cross-anharmonic couplings between the ferroelectric phonon and other normal-mode lattice vibrations.…”

Section: B Dielectric Function and Polariton Response Of A Ferroelecmentioning

confidence: 99%

“…Crystals for which a strong low-frequency dielectric response rises near the phase-transition temperature (relaxational or central mode) were denoted as order-disorder Dougherty, Wiederrecht, and Nelson, 1991;Dougherty et al, 1994). However, for several ferroelectrics both relaxational modes Chowdhurry et al, 1978) and mode softening (Johnston and Kaminow, 1968;Servoin and Gervais, 1979;Okamoto et al, 1985;Zhang and Scott, 1986) were observed and it was not clear whether the phase transitions of these ferroelectrics are of displacive or order-disorder type.…”

Section: Introductionmentioning

confidence: 99%

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Coherent phonon polaritons as probes of anharmonic phonons in ferroelectrics

1998

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In the last decade it has been shown that the low-frequency dielectric response of ferroelectrics can be investigated with great sensitivity via the impulsive excitation and phase-sensitive detection of ultrashort THz phonon-polariton wave packets. In this paper the authors review this technique and the new information obtained with it on the dielectric response and phonon properties of ferroelectrics. The technique is demonstrated with measurements on the perovskite ferroelectrics LiTaO 3 and LiNbO 3 . The results are compared with those of other time-resolved studies on phonon polaritons and continuous-wave Raman and infrared-reflectivity studies on LiTaO 3 , LiNbO 3 and other ferroelectric crystals. For several ferroelectrics, the polariton dispersion and polariton damping are observed to be strongly influenced by the presence of resonances at frequencies below the fundamental ferroelectric phonon frequency. The occurrence of these resonances is explained from the intrinsic anharmonicity of the ferroelectric phonon or from cross-anharmonic couplings between different normal-mode lattice vibrations. [S0034-6861(98)00502-9]

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Section: Resultsmentioning

confidence: 66%

Section: B Dielectric Function and Polariton Response Of A Ferroelecmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Coherent phonon polaritons as probes of anharmonic phonons in ferroelectrics

1998

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“…The difference between the two types is whether the double-well potential energy surface (PES) around the paraelectric phase is only along a collective displacement of the cation sublattice or along a lot of local displacements of individual cations. In several experimental reports on LiNbO 3 , [10][11][12][13][14][15] Raman spectroscopy and infrared reflectivity measurements observed a soft mode, indicating a displacive phase transition, 10,11 while other reports on the neutron and Raman scattering measurements did not observe such a soft mode, suggesting an orderdisorder phase transition. 13,14 In addition, phonon analyses and molecular dynamics (MD) simulations were performed using first-principles calculations and empirical inter-atomic potentials in several theoretical reports.…”

mentioning

confidence: 93%

First-principles study on phase transition and ferroelectricity in lithium niobate and tantalate

Toyoura

Ohta

Nakamura

et al. 2015

Journal of Applied Physics

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The phase transitions and ferroelectricity of LiNbO3 and LiTaO3 have been investigated theoretically from first principles. The phonon analyses and the molecular dynamics simulations revealed that the ferroelectric phase transition is not conventional displacive type but order-disorder type with strong correlation between cation displacements. According to the evaluated potential energy surfaces around the paraelectric structures, the large difference in ferroelectricity between the two oxides results from the little difference in short-range interionic interaction between Nb-O and Ta-O. As the results of the crystal orbital overlap population analyses, the different short-range interaction originates from the difference in covalency between Nb4d-O2p and Ta5d-O2p orbitals, particularly dxz-px/dyz-py orbitals (π orbitals), from the electronic point of view.

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“…13 It was suggested that the CP in Raman scattering is not a central mode which occurs in addition to onephonon spectral features. It is rather one of the 4A 1 normal modes, which becomes nearly soft and heavily overdamped near T C .…”

Section: Introductionmentioning

confidence: 99%

Ferroelectric phase transition of stoichiometric lithium tantalate studied by Raman, Brillouin, and neutron scattering

et al. 2007

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The ferroelectric phase transition of nearly stoichiometric LiTaO 3 crystals with very low lithium deficiency has been studied by Raman, Brillouin, and neutron scattering. The neutron elastic scattering shows the high value of the Curie temperature T C = 960 K in comparison with T C = 873 K of the congruent crystals. In order to make clear the order-disorder character near the Curie temperature, the central peak ͑CP͒ ͑quasielastic scattering͒ has been investigated by the broadband Brillouin scattering and low-frequency Raman scattering in the wide temperature range of 300-1067 K. In Brillouin and Raman scattering, CP is observed at the polarized scattering geometry in all the temperatures studied. The polarized nature of CP indicates that its origin is the polarization fluctuation along the ferroelectric c axis. It is found that the relaxation time determined from the width of CP clearly shows a critical slowing down of an order-disorder phase transition in the vicinity of T C .

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Soft vibrational mode in LiNbO3 and LiTaO3

Cited by 56 publications

References 11 publications

Coherent phonon polaritons as probes of anharmonic phonons in ferroelectrics

Coherent phonon polaritons as probes of anharmonic phonons in ferroelectrics

First-principles study on phase transition and ferroelectricity in lithium niobate and tantalate

Ferroelectric phase transition of stoichiometric lithium tantalate studied by Raman, Brillouin, and neutron scattering

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