Plasma spray synthesis works for zirconia so that no extra calcination is needed. It gives tetragonal phase particles of different morphology such as bubbles and solid balls.
Metastable tetragonal phase zirconia (IV) with improved thermal stability was obtained by precipitation from aqueous solution of the precursor of zirconium salts, followed by drying and calcining. As substrates were used: ZrO(NO3)2, or ZrOCl2. Hydrated precursor was prepared by precipitating with 25% aqueous ammonia solution of a zirconium salt solution (pH about 12). Precursor samples were precipitated in each case dried for 12 hours at a temperature of about 105C. The thus obtained precursor was amorphous, as shown X-ray diffraction measurement. It remained amorphous even after calcination at 355C for 45 min. Further calcination at the same temperature for 1.5 h to give pure metastable tetragonal phase. Better results are obtained with ZrOCl2.
In my works I'm using laser ablation to obtain t- and c- phase Zirconia nanoparticles. In addition it's possible to synthesise t-phase zirconia with help of autoclave sinthesis at critical size of particles