Stability of metastable tetragonal ZrO2 in compound powders and nucleation arguments

ZrO₂-SiO₂ (11) mixtures and ZrO₂ particles were prepared by a sol-gel method from the solutions of ZrOCl₂·8H₂O (ZOC) + Si(OC₂H₅)₄ (TEOS) + C₂H₅OH and ZOC + C₂H₅OH + H₂O + NH₄Cl systems, respectively. Quantitative changes of phase crystallized by heating were compared with those of ZOC + TEOS + H₂O and/or ZrO(NO₃)₂ · 2H₂O + H₂O systems, respectively. The stability of metastable tetragonal (mt)-ZrO₂ particles depends on the Young's modulus of the SiO₂ matrix. Transition metal oxides existing on the interface assisted in stabilizing mt-ZrO₂. The order of the assistance agreed with that of the relative field strengths of their oxides. A relationship between the ionic radius and the volatility of anionic groups, and the difficulty of nucleation for the martensitic transformation accompanying a shear stress, is suggested.