Multinuclear MAS NMR Investigation of Sol-Gel and Ball-Milled Nanocrystalline Ga2O3

Abstract

71Ga magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to characterize the structural evolution of nanocrystalline Ga2O3 samples prepared by sol-gel and ball-milling techniques. 29Si and 27Al MAS NMR have also been used to characterize silica and alumina Zener pinning phases. 71Ga NMR parameters are reported for the α- and β-Ga2O3 phases, and more tentatively for the δ-Ga2O3 phase. By simulating the octahedrally coordinated gallium NMR line of β-Ga2O3 using Gaussian distributions in χQ, the extent of disorder in the Ga2O3 crystallites has been quantified. The ball-milled samples contain much more inherent disorder than the sol-gel samples in the nano-phase, which was observed from simulations of the 71Ga MAS NMR spectra. The silica pinning phase produced highly crystalline and densely aggregated nanocrystalline Ga2O3, as well as the smallest nanocrystal sizes.