Abstract
In the Earth's mantle, the mechanism(s) of solid solution of Al in MgSiO 3 perovskite strongly impacts its thermodynamic and transport properties. We present 2 7 Al N MR data for perovskite samples of nominal composition Mg(Si 0 . 9 Al 0 . 1 )O 2 . 9 5 , to test a mechanism by which Al 3 + substitutes at the octahedral Si 4 + sites, leaving a corresponding number of O-site vacancies. We find evidence for this process in a significantly greater peak area for Al at B (Si) sites vs. A (Mg) sites in the structure, and the possible identification of a small concentration of five-coordinated Al adjacent to such vacancies. However, substitution of Al 3 + at the A sites remains significant. As in perovskite-type technological ceramics, O-atom vacancies may play an important role in enhancing ion mobility and the dissolution of water.
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