Optical Investigation of Na₂V₃O₇ Nanotubes

Abstract

We report the electronic and vibrational properties of Na 2 V 3 O 7 nanotubes and compare the response with other layered and nonlayered vanadates. The electronic structure of Na 2 V 3 O 7 displays a strong similarity to that of nontubular vanadates. We assign the 1.2-eV band as a V d f d excitation and the 3.3-and 3.9-eV bands as O 2p f V 3d charge-transfer structures. Although band structure calculations predict additional fine structure in the density of states because of the tubular morphology, such features are not observed in the absorption spectrum. The vibrational spectrum displays triplet mode splitting as a result of reduced site symmetry, consistent with the three sightly different vanadium atoms that form the basic structural unit. A low-frequency rattling mode is observed in Na 2 V 3 O 7 at 88 cm -1 . This unique characteristic of the Na + -ion intercalated tubes might be connected with the ionic conductivity.

Unusual magnetic properties of the low-dimensional quantum magnetNa2V3O7

“…For 1D systems, a simple dimerization generally leads to observable changes in the crystal structure. Such changes have been searched for, but were not observed in optical studies [11]. From our results it is suggested that the V − V couplings involve a broad range of interactions and given the unusual structural features of Na 2 V 3 O 7 , which may include some randomness, it is not clear that changes in the structure that could be detected in scattering and/or optical experiments should be expected here.…”

“…with γ = 35 mJ/(mol K 2 ) and C DE , emphasized by the dotted line, representing the specific heat of the lattice due to acoustic phonons (Debye model with Θ D = 125 K) and the lowest optical mode (Einstein model) at 88 cm −1 [11]. The temperature variation according to Eq.…”

Novel Nanostructures of Functional Oxides Synthesized by Thermal Evaporation

“…They also have a rectangular cross section enclosed by ±(010) and ±(101 Å ) facet planes, but the width-to-thickness ratio is 2±5, smaller than that for SnO 2 nanobelts (5±10). The growth direction of the SnO 2 nanowires is also parallel to the [101] crystal direction (Fig. 4b).…”

“…3c) and high-resolution TEM (HRTEM) images ( Fig. 3b) reveal that an individual nanobelt is a single crystal of the rutile structure with lattice constants a = 4.722 and c = 3.184 , [119] and SnO 2 nanobelts grow along the [101] crystal direction and terminate in ± (010) and ± (101 Å ) crystallographic facets (Fig. 3d).…”

“…6a). The inserted electron diffraction pattern in Figure 6b is to the [101] crystal zone of b-Ga 2 O 3 . The two perpendicular planes result in the rectangular and L-shaped structures (Fig.…”