Light-induced variations in realgar and beta -As₄S₄; X-ray diffraction and Raman studies

Abstract

Other| August 01, 1996 Light-induced variations in realgar and beta -As 4 S 4 ; X-ray diffraction and Raman studies P. Bonazzi; P. Bonazzi Universita di Firenze, Dipartimento di Scienze della Terra, Florence, Italy Search for other works by this author on: GSW Google Scholar S. Menchetti; S. Menchetti Search for other works by this author on: GSW Google Scholar G. Pratesi; G. Pratesi Search for other works by this author on: GSW Google Scholar M. Muniz-Miranda; M. Muniz-Miranda Search for other works by this author on: GSW Google Scholar G. Sbrana G. Sbrana Search for other works by this author on: GSW Google Scholar Author and Article Information P. Bonazzi Universita di Firenze, Dipartimento di Scienze della Terra, Florence, Italy S. Menchetti G. Pratesi M. Muniz-Miranda G. Sbrana Publisher: Mineralogical Society of America First Online: 02 Mar 2017 Online ISSN: 1945-3027 Print ISSN: 0003-004X Copyright © 1996 by the Mineralogical Society of America American Mineralogist (1996) 81 (7-8): 874–880. https://doi.org/10.2138/am-1996-7-810 Article history First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation P. Bonazzi, S. Menchetti, G. Pratesi, M. Muniz-Miranda, G. Sbrana; Light-induced variations in realgar and beta -As 4 S 4 ; X-ray diffraction and Raman studies. American Mineralogist 1996;; 81 (7-8): 874–880. doi: https://doi.org/10.2138/am-1996-7-810 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Transformations induced by light in realgar and β-As4S4 have been studied by means of X-ray diffraction (powder and single-crystal) and Raman laser spectroscopy. Both polychromatic and monochromatic light alter realgar and the β phase into pararealgar. By lowering the reaction rate (long-wavelength pass filter, low laser power) an intermediate product, corresponding to the so-called "x phase," can be observed during the alteration process from β-As4S4 to pararealgar (polychromatic filtered light and laser light) and that from realgar to pararealgar (only with polychromatic filtered light). The powder pattern of the x phase is fairly similar to that of β-As4S4 but differs from realgar, and it can be indexed on the basis of an expanded β-phase unit cell. Lattice parameters are as follows: a = 9.758(5), b = 9.522(5), c = 9.074(5) Å, β = 100.84(5)°, and a = 9.757(4), b = 9.512(7), c = 9.089(4) Å, β = 100.97(3)° for the x phase obtained from alteration of realgar and β-As4S4, respectively. The formation of the χ phase is preceded by a strong anisotropic increase of the unit-cell volume of realgar and the β phase. The effects of light exposure on lattice parameters were studied using single-crystal X-ray diffraction: In realgar a and c sin β increase linearly with increasing exposure times, whereas b remains substantially unchanged. In the β-As4S4 crystals, b and c sin β increase while a decreases so that, after 1560 min, the unit-cell dimensions match those of the χ phase. Raman spectroscopy, which allows monitoring of the alteration process in real time, indicates the presence of the same As4S4 cage molecule in the χ phase as in realgar and β-As4S4 and confirms the similarity between the structure of χ and that of β. However, a less-ordered crystal structure and a lower molecular symmetry is suggested from analysis of the spectroscopic results. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.