Local order of V⁵⁺ ions in borate glasses investigated EXAFS

ISSN： 0031-9090

Source： Physics and Chemistry of Glasses - European Journal of Glass Science and Technology Part B, Vol.41, Iss.5, 2000-10, pp. : 300-303

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Abstract

Glasses in the systems Li₂O–B₂O₃–V₂O₅ and ZnO–B₂O₃–V₂O₅ as well as crystalline reference substances were investigated by V-K-EXAFS. The glasses have a high modifier content ([Li₂O, ZnO]/[B₂O₃] ratio>1) and contain 10–50 mol% V₂O₅. The V–O interatomic distance, coordination number and Debye–Waller factor were determined from the analysis of the measured absorption spectra. In the glasses investigated (and in binary lithium or zinc vanadate glasses too) VO₄ tetrahedra are the predominant coordination polyhedra for the vanadium ions. The symmetry of the tetrahedra is more or less distorted in comparison to crystalline substances. The VO₄ tetrahedra can be either directly connected to each other or incorporated into borate BO₃/BO₄ groupings. Structural elements which are comparable to those in crystalline substances can be discussed. In glasses of the metaborate composition, vanadium can be incorporated in chain or ring [BØ₂O⁻]_n metaborate groupings. With increasing V₂O₅ content the vanadium ions can extensively replace boron ions and form distorted tetrahedra in VØ₂O₂⁻ metavanadate groups. In glasses of high modifier content and low vanadium amount the vanadium ions create nearly regular tetrahedra of isolated VO₄³⁻ ortho- or V₂ØO₆⁴⁻ pyrovanadate groups in the presence of B₂ØO₄⁴⁻ pyroborate, BO₃³⁻ orthoborate and BØ₄⁻ groups.