Neutron powder diffraction study of hydrogarnet to 9.0 GPa

Abstract

Other| October 01, 1996 Neutron powder diffraction study of hydrogarnet to 9.0 GPa George A. Lager; George A. Lager University of Louisville, Department of Geography and Geosciences, Louisville, KY, United States Search for other works by this author on: GSW Google Scholar Robert B. Von Dreele Robert B. Von Dreele Los Alamos National Laboratory, United States Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (9-10): 1097–1104. https://doi.org/10.2138/am-1996-9-1006 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation George A. Lager, Robert B. Von Dreele; Neutron powder diffraction study of hydrogarnet to 9.0 GPa. American Mineralogist 1996;; 81 (9-10): 1097–1104. doi: https://doi.org/10.2138/am-1996-9-1006 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu nav search search input Search input auto suggest search filter All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract The crystal structure of synthetic, deuterated katoite [Ca3Al2(O4D4)3] has been refined at 0.0001, 0.78, 3.6, 6.1, 7.9, and 9.0 GPa using the opposed-anvil Paris-Edinburgh cell and the POLARIS powder diffractometer at the U.K. pulsed spallation source, ISIS. A constrained Birch-Mumaghan fit to the unit-cell volume yields K0 = 52(1) GPa for K0´⁠, = 4.0. The lower bulk modulus of katoite relative to anhydrous Ca-bearing garnets (K0 = 159-179 GPa) is due to the greater compressibility of the Ca dodecahedron and O4D4 tetrahedron. At high pressure, corner-sharing tetrahedra and octahedra undergo a rigid-body rotation, which causes a shift in the O position. This rotation, coupled with the large compression of the two tetrahedral edges shared with the dodecahedron, changes the relative lengths of the Ca-O bonds at high pressure, such that Ca2-0 < Cal-O for P > 6 GPa. With increasing pressure, the O-D· · ·O angles widen slightly, as the O-D vector rotates toward the tetrahedral face. Both O-D and O· · ·D bond lengths decrease as a function of pressure, which was unexpected in view of the results of recent high-pressure studies. Comparison of crystallographic and spectroscopic data collected at high pressure for hydrogamets suggests that empirical relationships derived for hydrogen-bond systems at ambient conditions, where a relaxed, equilibrium state is attained, may not always apply to O-D · · · O hydrogen bonds under compression. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not currently have access to this article.