Infrared study of the phonon modes in PrMnO3 and CaMnO3

Abstract

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.

Temperature- and doping-dependent optical absorption in the small-polaron systemPr1−xCaxMnOMildner1, Hoffmann2, Blöchl3 et al. 2015Phys. Rev. B392352View full textAdd to dashboardCite

“…In addition, the obtained vibrational energies E (A) vib (T ) basically reveal the expected temperature trends, i.e., an almost temperature-independent behavior characterized by the zero-point phonon energy for T < D 2 ∼ 150 K and a linear increase with a slope of roughly kT at higher temperatures indicating thermal phonon broadening of the polaron absorption bands. The deviation from this temperature trend for x = 0.2, i.e., the decrease of E (A) vib (T ) at low temperature may be attributed to the presence of the ferromagnetic insulating (FMI) phase at T < 180 K. Moreover, the vibrational energies governing small polaron hopping transfer at T = 80 K in hole doped PCMO (x 0.5), E (A) vib = 1 2 ω (A) 0 ∼ 18-30 meV, are roughly consistent with a band of vibrational Mn-O-Mn tilt modes found in the energy range of ω 0 ∼ 30-50 meV in PCMO at various doping levels [18,42,43,45]. These modes change the octahedral tilting angle between nearest neighbor sites and, thus, may facilitate the intersite hopping transfer.…”

Vibrational spectra of CaGa2O4, Ca2GeO4, CaIn2O4 and CaSnO3 prepared by electrospinning

“…Observed Raman and IR bands for CaGa 2 O 4 , Ca 2 GeO 4 , CaIn 2 O 4 , CaSnO 3 and the bands assignment Modes involving the displacements of the apical oxygen and Ca 2+ atoms[46] …”

High-pressure investigation ofCaTiO3up to 60 GPa using x-ray diffraction and Raman spectroscopy

“…The calculated Raman frequencies for CaMnO 3 , on which the mode assignment is based, is also recalled. For comparison, the results of the shell model calculations for CaMnO 3 by Sopracase et al [50] are also indicated. Their model was successfully fitted against the infrared active frequencies, but shows marked differences to the Raman frequencies.…”