Crystal structure of morimotoite from Ice River, Canada. Issue 4 (30th April 2014)

• Record Type: Journal Article
• Authors: Antao, Sytle M.
• Is Part Of: Powder diffraction. Volume 29:Issue 4(2014)
• Page Start: 325
• Page End: 330
• Publication Date: 2014-04-30
• Subjects: Powder metallurgy -- Periodicals; Materials -- Analysis -- Periodicals; 620.1127
• DOI: 10.1017/S0885715614000414
• Languages: English
• ISSNs: 0885-7156

Abstract

<abstract abstract-type="normal"> <title> <x content-type="archive" xml:space="preserve">Abstract</x> </title> <p>The crystal structure of a morimotoite garnet, ideally Ca<sub>3</sub>(Ti<sup>4+</sup>Fe<sup>2+</sup>)Si<sub>3</sub>O<sub>12</sub>, from the Ice River alkaline complex, British Columbia, Canada was refined by the Rietveld method, space group <inline-formula><alternatives><inline-graphic xlink:href="ark:/27927/pgj46r65qb" xlink:type="simple" xmlns:xlink="http://www.w3.org/1999/xlink" /><tex-math><![CDATA[$Ia\overline 3 d$]]></tex-math></alternatives></inline-formula>, and monochromatic synchrotron high-resolution powder X-ray diffraction (HRPXRD) data. Electron-microprobe analysis indicates a homogeneous sample with a formula {Ca<sub>2.91</sub>Mg<sub>0.05</sub>Mn<sup>2+</sup><sub>0.03</sub>}<sub>Σ3</sub>[Ti<sub>1.09</sub>Fe<sup>3+</sup><sub>0.46</sub>Fe<sup>2+</sup><sub>0.37</sub>Mg<sub>0.08</sub>]<sub>Σ2</sub>(Si<sub>2.36</sub>Fe<sup>3+</sup><sub>0.51</sub>Al<sub>0.14</sub>)<sub>Σ3</sub>O<sub>12</sub>. The HRPXRD data show a two-phase intergrowth. The reduced <italic>χ</italic><sup>2</sup> and overall <italic>R</italic>(<italic>F</italic><sup>2</sup>) Rietveld refinement values are 1.572 and 0.0544, respectively. The weight percentage, unit-cell parameter (Å), distances (Å), and site occupancy factors (sofs) for phase-1 are as follows: 76.5(1)%, <italic>a</italic> = 12.156 98(1) Å, average <Ca–O> = 2.4383, Ti–O = 2.011(1), Si–O = 1.693(1) Å, Ca(sof) = 0.943(2), Ti(sof) = 0.966(2), and Si(sof) = 1.095(3). The corresponding values for phase-2 are 23.5(1)%, <italic>a</italic> = 12.160 67(2) Å, average <Ca–O> = 2.452, Ti–O = 1.988(3), Si–O = 1.704(3) Å, Ca(sof) = 1.063(7), Ti(sof) = 1.187(7), and Si(sof) = 1.220(8). The two phases cause strain that arises from structural mismatch and gives rise to low optical anisotropy. Because the two phases are structurally quite similar, a refinement using a single-phase model with anisotropic displacement parameters shows no unusual displacement ellipsoid for the O atom that requires a "split O-atom position", as was done in previous studies.</p> </abstract>