Raman spectroscopy of three polymorphs of BiVO₄: clinobisvanite, dreyerite and pucherite, with comparisons to (VO₄)³-bearing minerals: namibite, pottsite and schumacherite

Abstract

Both Raman and infrared spectroscopy have been used to characterise the three phase-related minerals—dreyerite (tetragonal BiVO₄), pucherite (orthorhombic BiVO₄) and clinobisvanite (monoclinic BiVO₄)—and a comparison of the spectra is made with that of the minerals namibite (Cu(BiO₂)VO₄(OH)), schumacherite (Bi₃O(OH)(VO₄)₂) and pottsite (PbBiH(VO₄)₂·2H₂O). Pucherite, clinobisvanite and namibite are characterised by VO₄ stretching vibrations at 872, 824 and 846 cm⁻¹. The Raman spectrum of dreyerite shows complexity in the 750 to 950 cm⁻¹ region with two intense bands at 836 and 790 cm⁻¹ assigned to the symmetric and antisymmetric VO₄ modes. The minerals schumacherite and pottsite are characterised by bands at 846 and 874 cm⁻¹. In both the infrared and Raman, spectra bands are observed in the 1000–1100 cm⁻¹ region which are attributed to the antisymmetric stretching modes. The Raman spectra of the low wavenumber region are complex. Bands are identified in the 328 to 370 cm⁻¹ region and in the 404 to 498 cm⁻¹ region and are assigned to the ν₂ and ν₄ bending modes. The minerals namibite and schumacherite are characterised by intense bands at 3514 and 3589 cm⁻¹ assigned to the symmetric stretching vibrations of the OH units. Importantly, Raman spectroscopy enables new insights into the chemistry of these bismuth vanadate minerals. Raman spectroscopy enables the identification of the bismuth vanadate minerals in mineral matrices where paragenetic relationships exist between the minerals. Copyright © 2006 John Wiley & Sons, Ltd.