First preparation of nanocrystalline zinc silicate by chemical vapor synthesis using an organometallic single-source precursor

A method is presented to prepare nanocrystalline alpha-Zn2SiO4 with the smallest crystal size reported so far for this system. Our approach combines the advantages of organometallic single-source precursor routes with aerosol processing techniques. The chemical design of the precursor enables the preferential formation of pure zinc silicates. Since gas-phase synthesis reduces intermolecular processes, and keeps the particles small, zinc silicate was synthesized from the volatile organometallic precursor [{MeZnOSiMe3}(4)], possessing a Zn-methyl- and O-silyl-substituted Zn4O4-heterocubane framework (cubane), under oxidizing conditions, using the chemical vapor synthesis (CVS) method. The products ob-tained under different process conditions and their structural evolution after sintering were investigated by using various analytical techniques (powder X-ray diffraction, transmission electron microscopy, EDX analysis, solid-state NMR, IR, Raman, and UV/ Vis spectroscopy). The deposited aerosol obtained first (processing temperature 750degreesC) was amorphous, and contained agglomerates with primary particles of 12 nm in size. These primary particles can be described by a [Zn-O-Si] phase without long-range order. The deposit obtained at 900degreesC contained particles with embedded nanocrystallites (3-5 nm) of beta-Zn2SiO4, Zn1.7SiO4, and ZnO in an amorphous matrix. On further ageing, the as-deposited particles obtained at 900degreesC form alpha-Zn2SiO4 imbedded in amorphous SiO2. The crystallite sizes and primary particle sizes in the formed alpha-Zn2SiO4 were found to be below similar to50 nm and mainly spherical in morphology. A gas-phase mechanism for the particle formation is proposed. In addition, the solid-state reactions of the same precursor were studied in detail to investigate the fundamental differences between a gas-phase and a solid-state synthesis route.