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ABSTRACT: The reaction of either V(2)F(6)·4H(2)O or a mixture of 60 wt % VF(2)·4H(2)O and 40 wt % VF(3)·3H(2)O with a water-saturated gaseous mixture of 15-20 vol % hydrogen in argon leads to the formation of a new polymorph of V(3)O(5) crystallizing in the orthorhombic anosovite-type structure. Quantum-chemical calculations show that the anosovite-type structure is about 15 kJ/mol less stable than the corresponding monoclinic Magnéli phase. In addition, there are no imaginary modes in the phonon density of states, supporting the classification of the anosovite-type phase as a metastable V(3)O(5) polymorph. Susceptibility measurements down to 3 K reveal no hint for magnetic ordering.
Inorganic Chemistry 07/2012; 51(15):8524-9. · 4.60 Impact Factor
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ABSTRACT: A metastable bixbyite-type polymorph of vanadium sesquioxide, V(2) O(3) , has recently been synthesized, and it transforms to the corundum-type phase at temperatures around 550 °C. The possibility of a paramagnetic to canted antiferromagnetic or even spin-glass-like transition has been discussed. Quantum-chemical calculations on the density-functional theory level including explicit electronic correlation confirm the metastability as well as the semiconducting behavior of the material and predict that the bixbyite-type structure is about 0.1 eV less stable than the well-known corundum-type phase. Nonetheless, quasiharmonic phonon calculations manifest that bixbyite-type vanadium sesquioxide is a dynamically stable compound. Other possible V(2) O(3) polymorphs are shown to be even less suitable candidates for the composition V(2) O(3) . © 2012 Wiley Periodicals, Inc.
Journal of Computational Chemistry 06/2012; 33(26):2102-7. · 4.58 Impact Factor
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D Weber,
A Stork,
S Nakhal,
C Wessel,
C Reimann,
W Hermes,
A Müller,
T Ressler,
R Pöttgen,
T Bredow,
R Dronskowski,
M Lerch
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ABSTRACT: A metastable polymorph of vanadium sesquioxide was prepared by the reaction of vanadium trifluoride with a water-saturated gaseous mixture of 10 vol % hydrogen in argon. The new polymorph crystallizes in the bixbyite-type structure. At temperatures around 823 K a transformation to the well-known corundum-type phase is observed. Quantum-chemical calculations show that the bixbyite-type structure is about 9 kJ/mol less stable than the known corundum-based one. This result, in combination with the absence of imaginary modes in the phonon density of states, supports the classification of the bixbyite-type phase as a metastable V(2)O(3) polymorph. At ~50 K a paramagnetic to canted antiferromagnetic transition is detected.
Inorganic Chemistry 06/2011; 50(14):6762-6. · 4.60 Impact Factor
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ABSTRACT: Two-dimensional (2D) exchange nuclear magnetic resonance (NMR) spectroscopy carried out under magic
angle spinning (MAS) conditions is ideally suited to study site-specific Li diffusion parameters of cathode
materials required for the target-oriented development of so-called high-energy density 4 V-lithium-ion batteries.
In the present study, we took advantage of Li NMR hyperfine shifts to record temperature-variable 1D and
mixing-time dependent 2D exchange MAS 6Li NMR spectra on R-Li3VF6 serving as both a potential cathode
material as well as an application-oriented model substance with three magnetically inequivalent Li sites. By
comparing the NMR results with structural details of the material we were able to obtain detailed insights
into the migration pathways and Li exchange rates which are of the order of some hundreds of Li jumps per
second at approximately 340 K. Site-specific Li jump rates τ-1 reveal the electrochemically active sites and
provide information how to modify the material in order to increase its relatively low Li diffusivity found at
room temperature.
The Journal of Physical Chemistry C 07/2010; 114:19083–19088. · 4.80 Impact Factor
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JOURNAL OF PHYSICAL CHEMISTRY C. 114(44):19083-19088.
