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The distribution of Fe3+ and Ga3+ between two tetrahedral sites in melilites,Ca2(Mg,Fe3+, Ga,Si)3O7 |
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| Authors: | Masahide Akasaka Haruo Ohashi Isamu Shinno |
| Institution: | 1. Department of Geology and Mineralogy, Faculty of Science, Hokkaido University, 060, Sapporo, Japan 2. National Institute for Research in Inorganic Materials, Namiki 1-1, Sakura-mura, Niihari-gun, 305, Ibaraki, Japan 3. Institute of Earth Science, College of General Education, Kyushu University, 810, Fukuoka, Japan |
| Abstract: | The distribution of Fe3+ and Ga3+ between the two tetrahedral sites in three synthetic melilites has been studied by using 57Fe Mössbauer spectroscopy. In the melilite, (Ca2Ga2SiO7)50 (Ca2Fe3+GaSiO7)50 (mol %), the distribution of Fe3+ and Ga3+ in T1 and T2 sites is apparently random, which can be explained in terms of the electrostatic valence rule. However in the melilites, (Ca2MgSi2O7)52 (Ca2Fe3+GaSiO7)42 (Ca2Ga2SiO7)6 and (Ca2MgSi2O7)62 (Ca2Fe3+GaSiO7)36 (Ca2Ga2SiO7)2 (mol %), Fe3+ shows preference for the more ionic T1 site and Ga3+ for the more covalent T2 site. If the electronegativity of Ga3+ is assumed to be larger than that of Fe3+, the mode of distribution of Fe3+ and Ga3+ can be explained in terms of our previous hypothesis that a large electronegativity induces a stronger preference for the more covalent T2 site. |
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