Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

Abstract

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 m o % V,O, were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V" ions in the glassy matrix exists, and a transition temperature near -70°C was observed. As-cast glasses with high V,O, concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions a t +70° and -120°C, the Nee1 temperatures of VO, and V,O,, respectively.

Electron spin resonance studies of evaporated V2O5 and co-evaporated V2O5/B2O3 thin films

“…This type of behaviour of our films is consistent with that reported by other authors [27,28,30,39] that amorphous V20 s films exhibit a well-resolved hyperfine structure as compared to crystalline VzOs.…”

“…[261 studied the magnetic behaviour of xVzOs-{100-x)% AszO 3 glass and reported a change in the line width of ESR spectra due to coupling between V 3 +_V 4 + and V 4 + -V 4 § ions at different compositions. Friebele et al [27] and Nicula et al [26] suggested that the antiferromagnetic coupling between reduced vanadium ions (V 4+, V 3+, V 2+) in vanadate glasses reduces the concentration of V ~'+ ions. Friebele et al [27] further noted that as the concentration of V2Os in the vanadate glasses increases the concentration of V 4+ ions decreases.…”

“…Friebele et al [27] and Nicula et al [26] suggested that the antiferromagnetic coupling between reduced vanadium ions (V 4+, V 3+, V 2+) in vanadate glasses reduces the concentration of V ~'+ ions. Friebele et al [27] further noted that as the concentration of V2Os in the vanadate glasses increases the concentration of V 4+ ions decreases. Singh [4] recorded a weakly resolved hyperfine structure due to V 4+ ions for low concentration of Fe203 in TeOz-V2Os-FezO3 glasses at room temperature, whereas for higher concentration of FezO3 (3 mol %), the hyperfine structure of V 4 § ions completely disappeared due to exchange interaction between V 4 + ions and Fe 3 + ions.…”

Correlation Between Microstructure and Electrochemical Behavior of Amorphous V 2 O 5 ‐ P 2 O 5 in Lithium Cells

“…Some reduction of vanadium ions related to oxygen gas evolution during melting were observed. The reduced vanadium ratio (=c) increased with increasing P20~ content as indicated in other reports (29,30).…”

Electrochemical Reduction of Ag0.48VOPO4: A Mechanistic Study Employing X-Ray Absorption Spectroscopy and X-Ray Powder Diffraction

“…This change in peak intensity is most likely related to the ratio of vanadium sites with 4+ and 5+ oxidation states; in several previous studies it was shown that the intensities of the two vanadium K-edge pre edge peaks in lithium vanadium phosphate glasses were consistent with the V 4+ and V 5+ fraction as determined independently using EPR studies. [49][50][51][52] The crystal structure of Ag 0.48 VOPO 4 has two similar vanadium sites that each have a silver ion in close proximity at a distance of ∼3.7 Å. Depending on whether this silver site is vacant, the neighboring vanadium ions may have initially have either a 4+ or 5+ oxidation state.…”