Raspite and studtite: Raman spectra of two unique minerals

Abstract

The Raman and IR spectra of monoclinic naturally occurring raspite, a-PbWO 4 (space group P2 1 /a) were measured; it is irreversibly transformed to the tetragonal stolzite, b-PbWO 4 , by heating to 450 • C, and this process was followed by Raman spectroscopy. Assignments of fundamental modes are proposed. New data are also presented on single crystals of stolzite (space group I4 1 /a), and it is shown that raspite and stolzite can easily be distinguished by their Raman spectra. We also present Raman and IR spectroscopic data on natural and synthetic studtite, UO 4 ·4H 2 O, and its synthetic dehydration product metastudtite, UO 4 ·2H 2 O, the only two naturally occurring peroxide-containing minerals, and on partially deuterated synthetic forms of these materials. Assignments of fundamental modes are proposed and both TGA and DSC data are presented for studtite.

Effects of pressure on PbWO4-III

“…Another feature of Raman spectra shows that the most intense vibration is not the highest frequency vibration (the most intense mode at 870.5 cm -1 and the highest frequency mode at 916.6 cm -1 ), which is similar to the Raman spectra of isomorphous BaWO 4 -II (P2 1 /n) (Tan et al 2009), but is different from the Raman spectra of raspite (PbWO 4 -II) and stolzite (PbWO 4 -I) (Bastians et al 2004). The existence of only a single sharp and intense Raman peak of PbWO 4 -III also shows the difference from a couple of intense peaks at 899 and 914 cm -1 at 13.7 GPa in previously observed Raman spectrum of the phase interpreted as the PbWO 4 -III (Manjon et al 2006).…”

“…In PbWO 4 -III, the average W-O bond distance of WO 6 octahedra (1.96 Å ) (Richter et al 1976) is close to the 1.94 Å in raspite and remarkably longer than the 1.795 Å in the stolzite. Therefore, the frequency of WO 6 octahedra stretching mode in PbWO 4 -III is near raspite's 870 cm -1 but not stolzite's 910 cm -1 (Bastians et al 2004). This can be rationalized on the simplistic basis that the intense 870.5 cm -1 mode in PbWO 4 -III represents stretching mode of the WO 6 octahedra.…”

“…This feature indicates that the PbWO 4 -III is stable at least up to 14.6 GPa under hydrostatic conditions at room temperature. For the room pressure Raman spectra, 31 Raman bands are observed in a wavenumber range of 100-1,000 cm -1 , which are more than 13 and 18 Raman-active modes of the tetrahedral stolzite (PbWO 4 -I, I4 1 /a) and the monoclinic raspite (PbWO 4 -II, P2 1 /a) (Bastians et al 2004), respectively, but less than 72 Raman-active modes of the PbWO 4 -III (P2 1 /n) structure expected by the group theory analysis (C Raman = 36A g ? 36B g ) (Manjon et al 2006;Rousseau et al 1981).…”

Vibrational Spectroscopy of Complex Synthetic and Industrial Products

“…More interesting, it was noted that the chemical formula commonly used in the literature (Paktunc et al, 2003(Paktunc et al, , 2004Fillipi et al, 2004Fillipi et al, , 2007Garavelli et al, 2009) Ca 2 Fe 3 (AsO 4 ) 3 O 2 ·3H 2 O had a peculiar form in that the use of peroxide types of molecular g r o u p s w e r e u s e d b u t a l s o n o h y d r o x y l g r o u p s w e r e i n c l u d e d i n t h e f o r m u l a s a s i n yukonite. Interestingly, most of these works where the formula was written in that fashion had no reference given to the earlier work of Moore and co-workers (Moore & Ito, 1974; (Burns & Hughes, 2003;Bastians et al, 2004). The Raman spectra of arseniosiderite in our work and previous others (Filippi et al, 2007) did not appear to contain peroxo groups and as such it was determined that expressing the formulae as Ca 2 Fe 3 (AsO 4 ) 3 O 2 •3H 2 O was incorrect because it gives the wrong impression that peroxo units exist in arseniosiderite structure which is untrue.…”

Raman spectroscopy in art and archaeology

“…Within Raman spectroscopic research on archaeological and artistic objects, different disciplines can be distinguished. Some groups focus on ceramics, 12 -14 others on glasses, 15,16 mural paintings, 17 -19 works on paper, 20,21 geological materials, 22,23 corrosion products 24,25 and biomaterials. 26 -28 Pigments and binding media in painted artworks are often examined using Raman spectrosocpy.…”