Infrared-active phonons ofLaMnO3andCaMnO3

Abstract

The infrared absorption spectra of polycrystalline LaMnO 3 and CaMnO 3 measured in the frequency range of the transverse optical phonons are reported, discussed, and compared with calculations of the lattice dynamics. For LaMnO 3 the measured spectrum is consistent with the expected orthorhombic structure. For CaMnO 3 the spectrum reflects a symmetry lower than that of a cubic perovskite. We find a close correspondence between the spectra of the two materials which suggests a similarity in their structures. ͓S0163-1829͑99͒09441-2͔

Infrared Active Phonons and Optical Band Gap in Multiferroic GdMnO3Studied by Infrared and UV-Visible Spectroscopy

“…For instance, the mode at 379 cm −1 could be associated with B 2u mode expected at 388 cm −1 or with B 1u mode at 367 cm −1 . Nevertheless, the ω TO of the observed phonon modes are found in good agreement with those reported for the materials with approxilar crystal structure like polycrystalline NdMnO 3 [16], LaMnO 3 [17] and single crystal GdMnO 3 polarized along a-axis [13], as summarized in Table III. As for the microscopic motion of the phonon modes is concerned, the phonon modes at 85, 116, 169, 187, and 242 cm −1 involve the motion of Gd atoms relative to MnO 6 octahedra. The Gd atoms, being heavier in the GdMnO 3 system, vibrate at low frequency.…”

“…The low frequency external modes are due to the vibrations of R and MnO 6 , while the intermediate frequency range bending modes and the high frequency stretching modes mainly involve vibrations of oxygen octahedra [20]. Hence, the modes assignment will be made by comparing the phonon frequencies obtained from the fit with those found in lattice dynamics calculations [17,24] as given in Table II. From Table II it is clear that some of the phonon modes obtained from the fit cannot be assigned unambiguously.…”

“…These modes are usually called breathing modes as only oxygen atoms vibrate about their mean position relative to the Mn atoms. [17] and single crystal GdMnO3 [13].…”

Effect of heavy cation doping on thermal properties of LaMnO3

“…It is to be noted that the higher value of Debye temperature indicate the higher phonon frequencies of La 0.25 Ca 0.75 MnO 3 . These values are compared with the calculated and experimental values [19][20][21][22] of the parent compound LaMnO 3 in Table 2 to indicate the large effect of heavy doping on the thermal properties of LaMnO 3 . It can be inferred from the results on cohesive energy ( Table 2) that the stability of doped compound is quite less compared to the parent compound and this can be correlated to the observed distortions of the lattice compared to the parent compound.…”

Infrared Reflectivity Spectra of Manganite Thin Films Grown on Different Substrates

“…The phonon excitation spectrum has been studied in detail for the undoped LaMnO 3 [9,10], which has below ∼750 K the Jahn-Teller (JT) distorted orthorhombic (Pnma) structure. A theoretical analysis of the complete set of phonon modes in the doped compounds is still missing.…”