Synthesis and structural properties of zirconia-based nanocrystalline powders and fine-grained ceramics

The synthesis and structural properties of zirconia-based nanocrystalline powders and fine-grained ceramics are reviewed, emphasising the conditions required for the retention of the high temperature tetragonal and cubic phases, which are the most important ones for applications. Different methods for the synthesis of powders (coprecipitation, amorphous citrate process, sol-gel, polymerised complex method and gel-combustion) and for the preparation of ceramics are discussed. The equilibrium phase diagrams of the most commonly studied zirconia-based binary systems (ZrO2-Y2O3; ZrO2-MgO; ZrO2-CaO and ZrO2-CeO2) are considered and the domains of existence of the tetragonal and cubic phases are analysed, taking into account its relation with the preparation of ceramics that present these phases. The existence of three tetragonal forms in several compositionally homogeneous zirconia-based solid solutions (such as ZrO2-Y2O3; ZrO2-Er2O3; ZrO2-Nd2O3; ZrO2-Sm2O3; ZrO2-Yb2O3; ZrO2-CeO2 and ZrO2-CaO) is also reviewed, considering the influence of the crystallite size. Some discrepancies and topics not fully understood, which are nowadays subject of intense investigation, are discussed in detail.