Crystal structure study of a β′-copper vanadium bronze, Cu _x V₂O₅ (x = 0.63), by X-ray and convergent beam electron diffraction

Abstract

The single-crystal structure of a beta'-copper vanadium bronze, Cu0.63V2O5, has been studied at room temperature and 9.6 K, and compared with that of the beta-sodium vanadium bronze, Na0.33V2O5, structure. No convincing evidence to oppose an assignment of centrosymmetric C2/m symmetry to the structure was identified using the X-ray data. A subsequent convergent beam electron diffraction (CBED) experiment was performed and confirmed the C2/m space group. The oxygen-vanadium atom framework of Cu0.63V2O5 is close to that of Na0.33V2O5. However, in the copper compound the Cu atoms are located in two positions: Cu1 in the 4(i) position with x=0.541, y=0 and z=0.345, and Cu2 in the 8(j) position with x=0.529, y=0.038 and z=0.357. The crystal structure changes little with temperature. Disorder of the Cu ion over two sites is seen at 9.6 K. This suggests that distribution of the Cu atoms over two sites is of a more static than dynamic nature.

Theoretical Description, Synthesis, and Structural Characterization of β-Na0.33V2O5and Its Fluorinated Derivative β-Na0.33V2O4.67F0.33: Influence of Oxygen Substitution by Fluorine on the Electrochemical Properties

“…Though these values are in fair agreement with our results, they systematically overestimate the valence of vanadium. On the other hand, our values were also systematically lower than those reported by Streltsov for the bronze Cu 0.63 V 2 O 5 , which differ not only in the amount of monovalent tunnel ions but also with regard to the Na and Cu positions. Nevertheless, in agreement with Streltsov, the lowest valence is obtained for the V2 atom, which appears to be the vanadium ion with the highest charge from multipole analysis of the electron density in Na 0.33 V 2 O 5 and, furthermore, has been proposed to be strongly involved in the charge ordering in this sodium vanadium oxide bronze …”

Synthesis, Structural Characterization, and Electronic Structure of Single-Crystalline CuxV2O5 Nanowires

“…Because of variable copper content, convergent beam electron diffraction at low temperature has been used to establish the C2/m space group assignment for these β′ vanadium bronzes. 13 Figures 1 and 3 show noticeable differences in the relative intensities of reflections for samples prepared by hydrothermal reduction with different alcohols for varying times. These changes can be attributed to the strongly preferred orientation present in the 1D nanowire products that is somewhat retained even after mechanical grinding of the samples (which does not appear to break the nanowires).…”

“…The third distinct, vanadium site, V3, connects the double octahedra along the c -direction and has an edge-sharing square pyramidal local geometry. Because of variable copper content, convergent beam electron diffraction at low temperature has been used to establish the C2/m space group assignment for these β′ vanadium bronzes . Figures and show noticeable differences in the relative intensities of reflections for samples prepared by hydrothermal reduction with different alcohols for varying times.…”

“…The separation between chains of cations that are thus coordinated is significantly larger than for the β phase, approaching close to 3.7 Å . The smaller size and greater separation between cations allows the incorporation of significantly greater amounts of Cu ranging up to a theoretical maximum of x = 0.67 . In a series of articles, the groups of Ueda, Yamaura, and Yamada have painstakingly mapped out the phase diagram of Cu x V 2 O 5 as a function of temperature, pressure, and Cu concentration. ,,, The ground-state of the β′ phase is characterized by metallic behavior for x > 0.40.…”

High pressure behavior of α-NaVO3: A Raman scattering study

“…Vanadium oxide-based compounds show rich variety of phenomena. Owing to the strong electron correlation, the b-vanadium bronzes have shown many interesting behavior such as charge ordering [4], pressure-induced superconductivity [5], etc. Orthovanadates of the type M 3 (VO 4 ) 2 (M: Ca, Sr, Ba) have excellent luminescence properties which are enhanced when doped with suitable rare-earth element, and find application as laser host materials [6].…”