Chemical behaviour of zirconium oxychloride octahydrate and acetic acid in precursor solution for zirconia film formation on glass

Abstract

Precursor solutions for zirconia films on soda lime silica glass substrate were prepared from zirconium oxychloride octahydrate (ZOO) and acetic acid (HOAC) maintaining the mol ratios, [HOAC]/[ZOO]=2, 4, 6, 8 and 10. A characteristic UV absorption band at ∼280 nm in the ∼120h aged precursor solutions was identified for acetate group of the zirconium acetato complexed species. The presence of acetate ligand coordinated with either ZrOOH⁺ or [Zr₄(OH)₈]⁸⁺ or with both was predicted by the studies of UV spectra of aged solutions and FTIR spectra of unbaked films on silicon wafer. Dipping technique was followed for film formation. Thicknesses and refractive indices of the baked (450°±5°C) films were in the ranges 1818±20 Å and 1.702–1.762 respectively. The positive SIMS experiment on two typical films baked at 450°±5°C derived from the precursors with [HOAC]/[ZOO]=2 and 6, detected the ionic species, Zr⁺, ZrO⁺, ZrO₂⁺, Na⁺, Ca⁺, Fe⁺, H⁺ while the negative SIMS detected O⁻ and Cl⁻. The relative contents of the ionic species with respect to Zr⁺ were dependent on the acid content of the precursors. Reflection (%) of the baked films in the UV region was also dependent on the acid content of the precursors. Electron diffraction pattern of the typical baked film derived from the precursor with [HOAC]/[ZOO]=2 exhibited meta-stable cubic phase of zirconia and the grains were found to be elongated (aspect ratio, 2.00–2.33).