Substructure and superstructure of four-layer Ca-exchanged birnessite

Abstract

Other| February 01, 1998 Substructure and superstructure of four-layer Ca-exchanged birnessite Victor A. Drits; Victor A. Drits Russian Academy of Sciences, Geological Institute, Moscow, Russian Federation Search for other works by this author on: GSW Google Scholar Bruno Lanson; Bruno Lanson Search for other works by this author on: GSW Google Scholar Anatoli I. Gorshkov; Anatoli I. Gorshkov Search for other works by this author on: GSW Google Scholar Alain Manceau Alain Manceau Search for other works by this author on: GSW Google Scholar American Mineralogist (1998) 83 (1-2): 97–118. https://doi.org/10.2138/am-1998-1-210 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 Victor A. Drits, Bruno Lanson, Anatoli I. Gorshkov, Alain Manceau; Substructure and superstructure of four-layer Ca-exchanged birnessite. American Mineralogist 1998;; 83 (1-2): 97–118. doi: https://doi.org/10.2138/am-1998-1-210 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 Synthetic Ca-exchanged birnessite (CaBi) was studied by X-ray and selected-area electron diffraction (XRD, SAED). The substructure of CaBi may be described with a four-layer monoclinic subcell with a = 5.150, b = 2.844, c = 4c' = 28.16 Aa, and beta = 90.3. Two different superstructures of CaBi were distinguished. CaBi type I has cell parameters A = 3a = 15.45, B = 3b = 8.472 Aa. The stacking sequence in this unit cell may be described as defect-free OSOS, where successive layers are shifted relative to their predecessors by 0 (O) or b/2 (S) along the b axis. The complete description of stacking involves the structure of the layer itself, the structure of the interlayer, and the shift from this layer to the next one. CaBi type II can be described as a regular interstratification of A P = 3/2(a-b), B P = 4b, gamma = 118.9 degrees and A P = 3/2(a+b), B P = -4b, gamma = 118.9 degrees supercells that are connected by a mirror plane in projection on the a-b plane. Its stacking sequence is a random interstratification of OSOS (90%) and OOOS (10%) structural fragments. Most CaBi crystals appeared to consist of intergrown type I and type II sub-crystals. As in Na-rich birnessite, the A = 3a superstructure arises from the ordered distribution of Mn (super 3+) -rich rows parallel to [010] and separated from each other along [100] by two Mn (super 4+) rows. In Mn (super 3+) -rich rows heterovalent Mn cations are regularly distributed according to Mn (super 3+) Mn (super 3+) Mn (super 4+) (CaBi type I, B = 3b) and Mn (super 3+) Mn (super 3+) Mn (super 4+) Mn (super 4+) (CaBi type II, B = 4b) sequences. Super-periodicities along the b axis are induced by these regular distributions of heterovalent Mn atoms in Mn (super 3+) -rich rows and of associated interlayer Ca. No significant amount of layer vacancies was detected. Idealized structural formulae for CaBi type I and II are Ca(Mn (super 3+) 2 Mn (super 4+) 7 )O 18 and Ca(Mn (super 3+) 2 Mn (super 4+) 10 )O 24 , respectively. 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.