Aluminum-Doped Zirconia Nanopowders: Chemical Vapor Synthesis and Structural Analysis by Rietveld Refinement of X-ray Diffraction Data

Zirconia nanoparticles doped with up to 50 mol % Al 2 O 3 were prepared by chemical vapor synthesis (CVS). XRD data of these powders were refined by Rietveld analysis. Doping with alumina decreases the fraction of the monoclinic ZrO 2 phase and stabilizes the tetragonal or cubic ZrO 2 phase, forming different ZrO 2 /Al 2 O 3 solid solutions. The tetragonal zirconia solid solution is obtained in the as-synthesized nanopowders doped with 3 and 5 mol % Al 2 O 3, whereas the cubic zirconia solid solution is formed in the nanopowder with 15 mol % Al 2 O 3 . Zirconia nanoparticles with higher alumina content (30 and 50 mol % Al 2 O 3 ) are amorphous and crystallize during annealing, forming the single-phase tetragonal ZrO 2 at 800 °C and a mixture of tetragonal ZrO 2 and γ- or η-Al 2 O 3 at 850 °C, respectively. During annealing, the stability of the high-temperature zirconia phases decreases considerably with increasing temperature. Thus, the cubic ZrO 2 phase transforms to the tetragonal. The tetragonality ( c / a ratio) and the fraction of the monoclinic ZrO 2 increase with temperature. Zirconia-alumina phase separation is observed in highly doped powders (≥15 mol % Al 2 O 3 ). The observed maximum solubility of alumina in the cubic/tetragonal zirconia is about 15 mol % Al 2 O 3 (or 26 at. % Al).