Multinuclear MAS NMR investigation of sol-gel and ball-milled nanocrystalline Ga2O3

Ga-71 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. Si-29 and Al-27 MAS NMR have also been used to characterize silica and alumina Zener pinning phases. Ga-71 NMR parameters are reported for the alpha- and beta-Ga2O3 phases, and more tentatively for the delta-Ga2O3 phase. By simulating the octahedrally coordinated gallium NMR line of beta-Ga2O3 using Gaussian distributions in chi(Q), 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 Ga-71 MAS NMR spectra. The silica pinning phase produced highly crystalline and densely aggregated nanocrystalline Ga2O3, as well as the smallest nanocrystal sizes