Coloured Synthetic zircon crystals. Flux growth and EPR of V4+ impurity centres

Abstract

The growth of blue and green zircon (ZrSiO4) crystals from fluxes consisting of (PbO + V2O5) and (3 Bi2O3 + V2O5), respectively, is reported. Vanadium is found in the crystals and EPR experiments show that it occurs, at least in part, as V4+ in sites of tetragonal symmetry. EPR is observed at X‐and Q‐band frequencies at temperatures of 20 and 4.2 K. The hyperfine constants are anisotropic and A‖ shows a marked temperature dependence. The spin Hamiltonian parameters at 20 K are g⊥ = 1.8930 ± 0.0008, A‖ = (81.6 ± 0.2) × X 10−4 cm−1, g⊥ = 1.9699 ± 0.0008, A‖ = (28.9 ± 0.2) × 10−4 cm−1. At 4.2 K: A‖ = (84.1 ± 0.2) × 10−4 cm−1.

Structural Evolution and Vanadium Distribution in the Preparation of V4+‐ZrSiO4 Solid Solutions from Gels

“…The above values are in agreement with values reported in the literature 3,5,20 and indicate the presence of V 4ϩ dissolved in the ZrSiO 4 lattice. In all compositions, independent of the nominal composition, the spectra show narrow signals and a practically horizontal base line.…”

Understanding the Interplay of Vacancy, Cation, and Charge Ordering in the Tunable Sc2VO5+δ Defect Fluorite System

“…We note that only few examples have been reported with V 4+ in tetrahedral coordination, and all of those structures contain distorted V 4+ −O 4 tetrahedra, e.g., monoclinic Re 2 VO 5 (Re = Y, Dy, Yb), 20 orthorhombic Sr 2 VO 4 , 39 monoclinic Ba 2 VO 4 , 40 cubic Ca 2 NaMg 2 V 3 O 12 , 41,42 vanadium-doped cubic Y 3 Al 5 O 12 , 43 and tetragonal ZrSiO 4 . 44,45 We propose that the tetrahedral 2c site in tetragonal Sc 2 VO 5+δ only accommodates V 5+ . This is consistent with four short 2c V−O bonds of 1.706(3) Å and 109.5(2)°tetrahedral O−V−O angles and a bond valence sum of 5.14 for V 5+ .…”

EPR of VO2+ in the Mineral Wavellite Al3(OH)3(PO4)2 · 5H2O

“…2 indicate absence of inhomogeneous broadening due to a large distribution of hfs constants which would lead to excess broadening of the outer components as observed in a number of systems including gar nets [10], zircon [11], apophyllite [2] and synthetic crystals [12]. Most likely unresolved hfs splitting due to the 27A1 and 31P nuclei in the neighborhood of the V 02+ contributes to the observed linewidths.…”