Computational and Experimental Investigation of the Transformation of V2O5 Under Pressure

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• 作者：J. M. Gallardo-Amores ; N. Biskup ; U. Amador ; K. Persson ; G. Ceder ; E. Mor&aacute ; n ; M. E. Arroyo y de Dompablo
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：October 30, 2007
• 年：2007
• 卷：19
• 期：22
• 页码：5262 - 5271
• 全文大小：606K
• 年卷期：v.19,no.22(October 30, 2007)
• ISSN：1520-5002

文摘

It has previously been reported that under high-pressure V₂O₅ (-V₂O₅) transforms into a layeredpolymorph, -V₂O₅, consisting of V⁵⁺O₆ octahedra instead of V⁵⁺O₅-square pyramids. Both polymorphshave a good performance as positive electrode for lithium batteries. In this work, we investigate thepressure-induced transformation combining first principles and experimental methods. Densityfunctional theory (DFT) predicts that -V₂O₅ transforms to -V₂O₅ at 3.3 GPa with a 11% volumecontraction; experiments corroborate that at a pressure of 4 GPa, V₂O₅ (d = 3.36 g/cm³) transformedinto a well-crystallized -V₂O₅, with a much denser structure (d = 3.76 g/cm³). -V₂O₅ can be alsoprepared at 3 GPa, although with a substantial degree of amorphization. The calculated bulk modulus of-V₂O₅ (18 GPa) indicates that this is a very compressible structure; this being linked to the contractionalong its b-axis (interlayer space) and to a significant decrease of a long V-O distance (V-O 2.9 Å).As a result, the vanadium coordination increases from five (square pyrmamid) in -V₂O₅ to six (distortedoctahedron), leading to the stabilization of the high-pressure () polymorph. This change of the coordinationenvironment of vanadium ions also affects the electrical conductivity. The calculated density of statesshows a narrowing of 0.5 V in the band gap for the polymorph, in comparison to the ambient-pressurematerial; the measured resistivities at room temperature (10 000 cm in -polymorph and 400 cmin -polymorph) reveal that -V₂O₅ is indeed a better electronic conductor than -V₂O₅. In view of theseresults, similar transformations at moderate pressures are expected to occur in other V⁵⁺ frameworks,suggesting an interesting way to synthesize novel V⁵⁺ compounds with potential for electrochemicaldevices.