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Petzelt, J.; Smutný, F.; Katkanant, V.; Ullman, F. G.; Hardy, J. R.; Volkov, A. A.; Козлов, Г. В.; Лебедев, С. П.

doi:10.1103/physrevb.30.5172

Cited by 20 publications

(6 citation statements)

References 23 publications

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“…the central peak and the soft phonon) that results in the spectral weight (intensity) transfer between the modes. 51 This is an important observation that resembles closely the reported behavior and phonon dynamics in Pb 5 Ge 3 O 11 , 52 Li 2 RuO 3 , 53 AgNbO 3 , 54 and Gd 2 (MoO 3 ) 4 51 in the low-frequency region. Such a behavior of the central peak is often connected with the internal relaxation processes of the crystal which are activated due to an interaction with the dynamical lattice defects, 20 phonon density as well as entropy fluctuations, 18,19 and motion of the domain walls.…”

Section: Signatures Of the Central Peak And Strong Anharmonicitysupporting

confidence: 83%

Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study

Badola

Mukherjee

Ghosh

et al. 2022

Phys. Chem. Chem. Phys.

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Section: Signatures Of the Central Peak And Strong Anharmonicitysupporting

confidence: 83%

Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study

Badola

Mukherjee

Ghosh

et al. 2022

Phys. Chem. Chem. Phys.

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“…A part of the effect can be understood if one takes into account that all AFD and FE soft modes are now polar and should mutually couple, so that the TO1 mode, whose frequency lies inside the AFD doublet, will repel the components of the latter. In order to obtain bare, uncoupled frequencies of the AFD and FE soft modes, we performed an additional fit using a three coupledoscillator model 45 for the soft-mode part of the spectra:…”

Section: Quasiepitaxial Sto1 Filmmentioning

confidence: 99%

Origin of soft-mode stiffening and reduced dielectric response inSrTiO3thin films

et al. 2002

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The problem of the reduced dielectric response in thin films of high-permittivity materials is analyzed by studying the soft-mode response in several SrTiO 3 thin films by means of Fourier transform far infrared, monochromatic submillimeter, and micro-Raman spectroscopies. A 300-nm-thick metalorganic chemical vapor deposition film, quasiepitaxially grown on a ͑0001͒ sapphire substrate with a perfect ͗111͘ orientation, displays a ferroelectric transition near 125 K induced by a tensile residual stress, appearing apparently simultaneously with the antiferrodistortive transition. On the other hand, polycrystalline chemical solution deposition films grown on ͑0001͒ sapphire, and also tensile stressed, show a harder soft mode response without the appearance of macroscopic ferroelectricity. This effect, which increases with the film thickness, is explained by a strong depolarizing field induced by the percolated porosity and cracks ͑in the 10-nm scale͒ along the boundaries of columnar grains ͑normal to the probe field direction͒. Brick-wall model calculations showed that 0.2 vol. % of such a porosity type reduces the permittivity from 30000 to less than 1000. The activation of the forbidden IR modes in the Raman spectra in the whole 80-300-K temperature range studied is explained by the effect of polar grain boundaries, in analogy with the bulk ceramics.

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“…We have discovered the soft mode which drives the phase transition; observations of this kind have been reported only rarely up to now. Previous lattice-dynamics studies of improper ferroelectrics revealed either no soft modes 19,20 or merely an overdamped excitation resolved as a central mode 18 . Even in hexagonal RMnO 3 manganites (R = Sc, Y, Dy-Lu) which exhibit improper FE phase transitions 12,15 analogous to 2H-BaMnO 3 , no soft modes were reported.…”

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confidence: 94%

“…The soft mode should become IR and Raman active below T C , but no such mode was revealed in recent IR 16 or Raman studies. 17 The lattice dynamics were studied also in other improper ferroelectrics, such as Gd 2 (MoO 4 ) 3 18 or boracites 19,20 , but no soft mode was detected 19,20 or it was markedly overdamped and therefore it was seen as a central mode. 18 Recently, Varignon and Ghosez 21 predicted an improper FE phase transition in the twolayered hexagonal BaMnO 3 (further denoted as 2H-BaMnO 3 ).…”

Section: Introductionmentioning

confidence: 99%

“…17 The lattice dynamics were studied also in other improper ferroelectrics, such as Gd 2 (MoO 4 ) 3 18 or boracites 19,20 , but no soft mode was detected 19,20 or it was markedly overdamped and therefore it was seen as a central mode. 18 Recently, Varignon and Ghosez 21 predicted an improper FE phase transition in the twolayered hexagonal BaMnO 3 (further denoted as 2H-BaMnO 3 ). Interestingly, in analogy with RMnO 3 , the phase transition should be driven by a K 3 -symmetry soft mode with q = ( 1 3 , 1 3 , 0) and the polarization should be induced by a coupling between the soft mode and a hard zone-center mode of Γ − 2 symmetry.…”

Section: Introductionmentioning

confidence: 99%

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Unusual ferroelectric and magnetic phases in multiferroic 2H−BaMnO3 ceramics

et al. 2017

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The structural phase transition in hexagonal BaMnO3 occurring at TC=130 K was studied in ceramic samples using electron and X-ray diffraction, second harmonic generation as well as by dielectric and lattice dynamic spectroscopies. The low-temperature phase (space group P 63cm) is ferroelectric with a triplicated unit cell. The phase transition is driven by an optical soft mode from the Brillouin-zone boundary [q = ( , 0)]; this mode activates in infrared and Raman spectra below TC and it hardens according to the Cochran law. Upon cooling below TC, the permittivity exhibits an unusual linear increase with temperature; below 60 K, in turn, a frequency-dependent decrease is observed, which can be explained by slowing-down of ferroelectric domain wall motions. Based on our data we could not distinguish whether the high-temperature phase is paraelectric or polar (space groups P 63/mmc or P 63mc, respectively). Both variants of the phase transition to the ferroelectric phase are discussed based on the Landau theory. Electron paramagnetic resonance and magnetic susceptibility measurements reveal an onset of one-dimensional antiferromagnetic ordering below ≈ 220 K which develops fully near 140 K and, below TN ≈ 59 K, it transforms into a threedimensional antiferromagnetic order.

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Central-peak—soft-mode coupling in ferroelectricGd2Gd2

Cited by 20 publications

References 23 publications

Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study

Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study

Origin of soft-mode stiffening and reduced dielectric response inSrTiO3thin films

Unusual ferroelectric and magnetic phases in multiferroic 2H−BaMnO3 ceramics

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Central-peak—soft-mode coupling in ferroelectricGd2Gd2

Cited by 20 publications

References 23 publications

Lattice dynamics across the ferroelastic phase transition in Ba2ZnTeO6: a Raman and first-principles study

Lattice dynamics across the ferroelastic phase transition in Ba2ZnTeO6: a Raman and first-principles study

Origin of soft-mode stiffening and reduced dielectric response inSrTiO3thin films

Unusual ferroelectric and magnetic phases in multiferroic 2H−BaMnO3 ceramics

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Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study

Lattice dynamics across the ferroelastic phase transition in Ba₂ZnTeO₆: a Raman and first-principles study