Raman phonons and the Jahn–Teller transition in RMnO3 manganites

Martı́n-Carrón, L.; Andrés, A. de

doi:10.1016/s0925-8388(01)01101-x

Cited by 32 publications

(10 citation statements)

References 11 publications

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“…The 480 cm −1 peak is associated with an out-of-phase bending mode of the oxygen cage where the O 2− ions vibrate perpendicular to the Mn-O line. The 480 cm −1 peak has been identified to couple with the e g electron in the well studied Jahn-Teller compound LaMnO 3 [9]. The low frequency modes are associated with rotations of the oxygen cage and do not involve internal distortions of MnO 6 .…”

Section: Resultsmentioning

confidence: 95%

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

et al. 2002

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Section: Resultsmentioning

confidence: 95%

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

et al. 2002

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“…The polarized Raman spectra of each compound, collected using laser excitation with different photon energy in the visible region, are practically identical, which shows that the resonance effects are negligible. It is worth noting here that this could not be concluded from the previous works 3,[5][6][7][8][9] because the spectra were obtained with a single laser line. Indeed, several papers on orthorhombic YMnO 3 report polarized 3,6,9 or nonpolarized 7,8 Raman spectra, obtained with either 515 nm or 633 nm laser excitation.…”

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confidence: 81%

“…It is worth noting here that this could not be concluded from the previous works 3,5-9 because the spectra were obtained with a single laser line. Indeed, several papers on orthorhombic YMnO 3 report polarized 3,6,9 or nonpolarized 7,8 Raman spectra, obtained with either 515 nm or 633 nm laser excitation. For YCrO 3 there is only one early paper 5 on the polarized Raman spectra using 515 nm.…”

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confidence: 99%

Comparative Raman study of isostructural YCrO3and YMnO3: Effects of structural distortions and twinning

et al. 2011

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Polarized Raman spectra of isostructural orthorhombic YCrO 3 and YMnO 3 single crystals were collected at same conditions using different laser excitation in the visible range. The symmetry of the observed lines was determined and they were assigned to definite atomic vibrations based on lattice dynamical calculations. The frequencies of the lines of the same origin in both compounds are close, however, their intensities differ significantly. While the different intensity of the modes, activated by the Jahn-Teller distortion, can be explained by the different magnitude of this distortion in the two compounds, the cause of the reduced intensity of other lines in low frequency region in the Raman spectra of YMnO 3 is likely due to the fine twinning of the crystal. INTRODUCTIONThe interest in the transition-metal perovskite-like oxides ABO 3 continues for decades because of many attractive phenomena observed in these compounds. Among them are structural second-order phase transitions, high-T c superconductivity, colossal magnetoresistance, charge-and orbital-ordering, complex magnetic properties, etc. As a rule the structural, electrical and magnetic properties of these compounds are strongly correlated. They can be tuned through the change of the mismatch of the A-O and B-O bond lengths, expressed by the tolerance factor t = (R A + R O )/ √ 2(R B + R O ), where R O , R A and R B are the ionic radii of the oxygen and atoms in the A-and B-positions, respectively. Depending on the value of t, most of these compounds crystallize in superstructures of the ideal cubic perovskite (space group Pm3m) with R3c or Pnma symmetry. Using the model of Glazer 1 , treating the BO 6 octahedra as rigid ones, the superstructures can be obtained from the ideal cubic perovskite through some tilts (rotations) of the octahedra around the main crystallographic directions. In the Glazer's notations, the rhombohedral R3c structure is of (a − a − a − ) type and the orthorhombic Pnma structure is of (a − b + a − ) type.Raman spectroscopy is a powerful experimental technique for study of perovskite-like oxides. Due to the fact that there are no Raman-active modes in the ideal cubic perovskite, all observed lines in the one-phonon region of the Raman spectra of the real perovskites have to be connected to some deviations of the real structure from the ideal one. For example, as shown in the pioneering work of Scott 2 , one of the Raman-active modes in the rare-earth aluminates of R3c structure consists in a rigid octahedral tilt around [111] direction. This mode can be considered as a "soft mode" and its frequency goes to zero as the temperature approaches the critical temperature of the structural second-order phase transition. Iliev et al. 3 have shown that in the case of rare-earth manganites with orthorhombic Pnma structure, two of the observed lines in the Raman spectra originate from modes with a shape of the two static octahedral tilts, existing in the structure. Although that these compounds do not undergo second order transition to...

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“…The structural determination of PrMnO 3 was obtained by neutron diffraction [23,24,25], and by X-ray diffraction [23]. Below ∼ 900 K, PrMnO 3 with the Pnma orthorhombic structure presents a strong JT cooperative distorsion of MnO 6 octahedra related to the ordering of the e g -orbitals [26], and undergoes at T N ≈ 95 K an A-type antiferromagnetic spin ordering [27]. The structure of CaMnO 3 is also described with the P nma space group at temperatures ranging up to at least 800 K [28].…”

Section: Introductionmentioning

confidence: 99%

Infrared study of the phonon modes in PrMnO3 and CaMnO3

Sopracase

Gruener

Olive

et al. 2010

Physica B: Condensed Matter

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The infrared (IR) reflectivity spectra of orthorhombic manganese perovskites PrMnO3 and CaMnO3 are studied in the frequency range of optical phonon modes at temperatures varying from 300 to 4 K. The IR phonon spectra of these two materials are analyzed by a fitting procedure based on a Lorentz model, and assigned to definite vibrational modes of P nma structures by comparison with the results of lattice dynamical calculations. The calculations have been performed in the framework of a shell model using short range Born-Mayer-Buckingham and long range Coulomb potentials, whose parameters have been optimized in order that the calculated Raman and IR active phonon frequencies, and lattice parameters match with their experimental values. We find a close correspondence between the values of the IR phonon frequencies of PrMnO3 and CaMnO3, which shows that the substitution of the Pr 3+ ions with Ca 2+ results in a reduction of the frequency of medium-and high-energy IR phonons, and an increase of the frequency of those of low-energy. Nevertheless, the experimentally obtained IR phonon amplitudes of the two materials appear to be unrelated. A comparative study of the vibrational patterns of these modes reveals that most of them correspond to complex atomic vibrations significantly different from PrMnO3 to CaMnO3 which cannot be assigned only to a given type of vibration (external, bending, or stretching modes). In particular, these results confirm that the structure of CaMnO3 is quite far from the ideal (cubic) perovskite structure.

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Raman phonons and the Jahn–Teller transition in RMnO3 manganites

Cited by 32 publications

References 11 publications

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

Polarized Raman scattering in single crystals of Nd0.7Sr0.3MnO3

Comparative Raman study of isostructural YCrO3and YMnO3: Effects of structural distortions and twinning

Infrared study of the phonon modes in PrMnO3 and CaMnO3

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