Microwave-assisted hydrothermal synthesis of nanocrystalline yttria-doped zirconia

An efficient microwave-assisted hydrothermal method was developed for the preparation of nanocrystalline 3 and 8 mol% yttria-doped zirconia (named as Z3Y and Z8Y, respectively) from commercially-available ZrOCl₂·8H₂O, YCl₃·6H₂O and KOH. The synthesis was conducted at low temperature (180 °C for sample Z3Y and 200 °C for sample Z8Y) and short reaction time (30 min) by simultaneous precipitation of both chlorides with KOH and dehydration of hydroxides. Analytical control of Zr and Y (standardization of stock solutions, precipitation degree) throughout the entire synthetic process was carried out by ICP-OES. Quantitative precipitation (greater than 99.999%) of both elements was obtained. The as-synthesized powders were calcined at 500 °C (sample Z3Y) and 800 °C (sample Z8Y), and all the resulting products were characterized by XRD, FE-SEM, HR-TEM and SAED. Both the as-synthesized and calcined nanoparticles were highly crystalline. The crystalline phases obtained were tetragonal phase (with a fraction of about 20% monoclinic) for sample Z3Y, and pure cubic phase for sample Z8Y. No impurities from other phases were detected. The average crystallite sizes for the as-synthesized samples Z3Y and Z8Y were 6.2 ± 1.0 and 3.5 ± 0.7 nm, respectively, while for the calcined ones the values were 8.0 ± 1.2 and 11.3 ± 1.3 nm, respectively.