Charge ordering and optical transitions ofLiV2O5and

Abstract

We present measurements of the polarized optical spectra of NaV 2 O 5 and LiV 2 O 5 . In an energy range from 0.5 to 5.5 eV, we observe similar peaks in the E a spectra of NaV 2 O 5 and LiV 2 O 5 , which suggests similar electronic structures along the a axis in both materials. On the other hand, we find an almost complete suppression of the peaks in σ b of LiV 2 O 5 around 1 and 5 eV. We attribute this suppression to the charge localization effect originating from the existence of a double-chain charge-ordering pattern in LiV 2 O 5 . : 78.40.-q, 71.35.-y, 75.50.-y In the past several years, quantum phenomena resulting from the low dimensionality of effective electron interactions in solids have been investigated with increasing intensity from both experimental and theoretical points of view. The increase in interest was partially motivated by the discovery of inorganic materials which exhibit quantum effects, such as the PACS, and by a common belief that these studies would give us a better understanding of electron correlations in general.The vanadate family of AV 2 O 5 oxides have demonstrated a variety of the low-dimensional phenomena which originate from their peculiar crystal structures [3]. These oxides are quasi two-dimensional (2D) materials with layers formed by V O 5 square pyramids. The A atoms are situated between layers as intercalants, but in fact they determine the valence state of vanadium atoms (acting as charge reservoirs). If the A atoms belong to the first column in the periodic table, such as A = Li, Na, each valence electron is shared between two vanadium atoms. As a result the V ions are in a mixed valence-state with an average valence of +4.5. The common consequence of mixed valence in these structures is the appearance of a quasi-1D magnetic interaction, since chains carrying the spin (made of V 4+ , S=1/2) are separated from each other by nonmagnetic chains (V 5+ ). In both LiV 2 O 5 and NaV 2 O 5 the 1D character of the magnetic ordering was confirmed [4,5]. In addition, there is a possibility of the existence of strong valence fluctuations, and eventually charge ordering (CO) effects.

Optical properties ofα′−NaxV2Konstantinović1, Popović2, Moshchalkov3 et al. 2002Phys. Rev. BSelf Cite144120View full textAdd to dashboardCite

“…For the nominally pure α ′ -NaV 2 O 5 the bands at the energies 0.9, 1.2, and 3.2 eV for σ a , and at 1.2, 1.6, and 3.7 eV for σ b are found in accordance with previous reports 20, 21,22,23 . The sodium deficiency causes the activation of the new optical transitions at about 2.8 eV in σ a and at 3.2 eV in σ b , see Fig.3.…”

“…Therefore, the optical transitions above 2 eV should also be similar in V 2 O 5 and α ′ -Na x V 2 O 5 . However, previous studies 20, 21,22,23 did not clearly show what kind of the final state is involved in the 3.2 eV (σ a ) transition, and this turns out to be the most important information in order to understand the electronic structure of the Na-deficient samples. If the final state is the bonding V3d xy state, as described in Ref.…”

Mapping polaronic states and lithiation gradients in individual V2O5 nanowires

“…With increasing lithiation, the donated electrons begin to occupy the non-bonding 3 d xy component at the band edge. We first consider a simple periodic system with a pure V 4.5+ site, where the electron occupies only a quarter of all available 3 d xy orbitals (as in α -NaV 2 O 5 )5154. Even at this electron doping level, electron correlation effects are important.…”

“…4c. The donated electrons take on 3 d xy character and the localized spins515455 are arrayed along the orthorhombic b -axis of V 2 O 5 . Contrary to intuition, the observed diminution of t 2g intensity is not due to Pauli blocking from electron occupation, as the Fermi level remains far below the main peak position in the quarter-filled case.…”

Charge excitations inLiV2O5andHübsch1, Waidacher2, Becker3 2001Phys. Rev. B7030View full textAdd to dashboardCite

“…12 In the energy range from 0 to 3 eV similar peaks in the Eʈa spectra of both materials were found. On the other hand, a complete suppression of the peaks in the Eʈb spectrum of LiV 2 O 5 was observed.…”