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

Abstract

A method is presented to prepare nanocrystalline α-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 obtained 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 750 °C) 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 900 °C contained particles with embedded nanocrystallites (3-5 nm) of β-Zn2SiO4, Zn1.7SiO4, and ZnO in an amorphous matrix. On further ageing, the as-deposited particles obtained at 900 °C form α-Zn2SiO4 imbedded in amorphous SiO2. The crystallite sizes and primary particle sizes in the formed α-Zn2SiO4 were found to be below 50 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.