Optical properties ofα′−NaxV2

Abstract

The optical properties of sodium-deficient α ′ -NaxV2O5 (0.85 ≤ x ≤ 1.00) single crystals are analyzed in the wide energy range, from 0.012 to 4.5 eV, using ellipsometry, infrared reflectivity, and Raman scattering techniques. The material remains insulating up to the maximal achieved hole concentration of about 15 %. In sodium deficient samples the optical absorption peak associated to the fundamental electronic gap develops at ∼ 0.44 eV. It corresponds to the transition between vanadium dxy and the impurity band, which forms in the middle of the pure α ′ -NaV2O5 gap. Raman spectra measured with incident photon energy larger then 2 eV show strong resonant behavior, due to the presence of the hole-doping activated optical transitions, peaked at ∼ 2.8 eV.

Pressure-induced changes in the optical properties of quasi-one-dimensionalβ−Na0.33V2O5

“…4 In α'-NaV 2 O 5 a similar broad Raman mode is found at around 650 cm −1 in aa polarization. 17,18,19,20,21,22 Several scenarios have been proposed to explain this broad Gaussian-like band: (i) electric dipole transitions between the crystal field split V 3d levels, (ii) magnon scattering, and (iii) a mode due to strong electron-phonon coupling. Up to now, a consensus has not been reached on this issue.…”

“…On the other hand, there are additional hints for the relevance of electron-phonon coupling in α'-NaV 2 O 5 : the phonon modes close to the broad band are asymmetric and could be fitted with a Fano profile. 17,20,23 Generally, such a mode asymmetry is assigned to the interaction between a discrete state (lattice vibration) and an electronic continuum. In coparison, in our ambientpressure cc Raman spectrum of β-Na 0.33 V 2 O 5 an asymmetric profile of the mode located at 518 cm −1 , close to the broad band at around 702 cm −1 , is not obvious.…”

Optical transitions in the two-leg ladder compoundsAxV6O15(A=

“…17 The origin of this peak is still unclear and may arise from a local excitation within the V1-O-V3 rung, 17,18 similarly to the two-leg ladder compound ␣Ј-NaV 2 O 5 . [19][20][21][22] In ␣Ј-NaV 2 O 5 , the two vanadium atoms of a rung are equivalent in the high-temperature phase and have thus the same charge and spin population. 22 Precisely, each valence electron is delocalized on a V-O-V rung in such a way that its state can be described by a linear combination of atomic orbitals.…”

Magnetodielectric effect in theS=1∕2quasi-two-dimensional antiferromagnetK2V3Rai1, Cao2, Musfeldt3 et al. 2006Phys. Rev. B250380View full textAdd to dashboardCite

“…Several modes show softening and splitting at low temperature, evidence of the 110 K structural distortion and a soft lattice. Based on vibrational properties studies in similar vanadyl oxide compounds, 67,68,69,70,71 the features of interest below 500 cm −1 can be assigned as V-O-V bending, O-V-O bending, and other low-energy tortional and twisting motions of the square pyramidal and tetrahedral building block units. The behavior of the 6.8 meV (55 cm −1 ) cluster (Fig.…”