A Solid-State NMR Study of Coordination Transformation in Amorphous Aluminum Oxide: Implication for Crystallization of Magma Ocean

Abstract

: In order to have better insights into the chemical differentiation of Earth from its magma ocean phase to the current stratified structure, detailed information of crystallization kinetics of silicate melts consisting of the magma ocean is essential. The structural transitions in oxide glasses and melts upon crystallization provide improved prospects for a systematic and quantitative understanding of the crystallization processes. Here, we report the 27 Al 3QMAS NMR spectra for sol-gel synthesized Al2O3 glass with varying temperature and annealing time. The NMR spectra for the amorphous Al2O3 show well-resolved Al coordination environments, characterized with mostly [4,5] Al and a minor fraction of [6] Al. The fraction of [5] Al in the alumina phase decreases with increasing annealing time at constant temperature. The NMR results of Al2O3 phases also imply that multiple processes (e.g., crystallization