MAS NMR spectroscopic study of Mg²⁹SiO₃ with the perovskite structure

A ²⁹Si MAS NMR spectroscopic study of three samples of MgSiO₃ perovskite with 95% isotopically enriched ²⁹Si prepared at 24 GPa and 1800 °C shows the following. 1) There is only one ²⁹Si peak, with a chemical shift of -191.7 ppm. 2) This peak is extremely narrow, with a Lorentzian shape and a full-width at half-height of 19-27 Hz (0.19-0.27 ppm). 3) The static peak shows no singularities attributable to chemical shift anisotropy (CSA). The peak breadth is probably substantially influenced by ²⁹Si dipole-dipole interaction. These results demonstrate that MgSiO₃ with the perovskite structure is extremely well ordered and that its Si coordination polyhedron is a very symmetrical octahedron. -from Authors