| Autor: |
Ballirano P; Department of Earth Sciences, Sapienza University of Rome, Piazzale Aldo Moro 5, I-00185 Rome, Italy., Celata B; Department of Energy Technologies and Renewable Sources, ENEA CR Casaccia, S. Maria di Galeria, 00123 Rome, Italy., Pacella A; Department of Earth Sciences, Sapienza University of Rome, Piazzale Aldo Moro 5, I-00185 Rome, Italy., Bloise A; Department of Biology, Ecology and Earth Science, University of Calabria, Via P. Bucci cubo 15b, I-87036, Arcavacata di Rende,CS, Italy., Tempesta G; Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari Aldo Moro, Via Orabona 4, 70125 Bari, Italy., Sejkora J; Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Praha 9, Czech Republic., Bosi F; Department of Earth Sciences, Sapienza University of Rome, Piazzale Aldo Moro 5, I-00185 Rome, Italy. |
| Abstrakt: |
Olivines are naturally occurring silicates consisting of isolated (SiO 4 ) 4- tetrahedra linked through M 1O 6 and M 2O 6 octahedra. In this study, we report the structural and crystal-chemical characterization of synthetic olivine crystals containing up to 25% Li-Fe 3+ synthesized using the flux growth technique. Based on site scattering, < M 1-O> and < M 2-O> mean bond lengths, and charge neutrality of the chemical formula, we found a perfect ordering of Li and Fe 3+ at the two distinct M 1 and M 2 sites. Unrestrained linear extrapolation to a hypothetical isostructural LiFe 3+ (SiO 4 ) composition aligns well with the tabulated ionic radii of Li and Fe 3+ . Comparison made with the isostructural LiSc(SiO 4 ) reveals that the Li-centered M 2O 6 octahedron has a significant capacity to distort in order to accommodate structural stresses, due to the relatively weak Li-O bond, while still achieving a bond valence sum that closely matches the formal charge of Li + . This behavior suggests the potential feasibility of an extended Li + Fe 3+ for 2 Mg coupled substitution within the olivine structure. The reported structure of the LiFe 3+ (SiO 4 ) endmember in the literature, despite its apparent matching of cell dimensions and space group with olivine, exhibits extremely unconventional crystal chemical features, raising questions about its validity. Given the importance of the suitability of Li-insertion in LiFeSiO 4 as electrodes in rechargeable Li-ion batteries, further studies are needed to investigate its crystal structure and crystal chemistry. |
