Influence of atmosphere on crystallization of zirconia from a zirconium alkoxide

Dibutoxybis (acetylacetonato) zirconium, a difunctional zirconium alkoxide, was polymerized at 130 °C for 5 hin vacuoto produce oligomers that could be pyrolyzed to form a tetragonal zirconia (t-ZrO₂), metastable at room temperature. This metastable phase was retained considerably below the equilibrium transformation temperature (∼1200 °C) without the use of dopants. Comparative pyrolysis of the oligomers between 600 and 900 °C in either flowing O₂or N₂for processing times under 12 h indicatedt-ZrO₂nucleated first. Pyrolysis in oxygen facilitated transformation to the monoclinic symmetry, whereas pyrolysis in nitrogen demonstrated retention of the tetragonal phase. The formation of oxygen vacancies during pyrolysis, their role in stabilizing the metastable tetragonal phase, and contributions of O₂and crystallite size in the polymorphic transformation are discussed.