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

The synthesis and structural properties of zirconia-based nanocrystalline p owders and fine-grained ceramics are reviewed, emphasising the conditions r equired for the retention of the high temperature tetragonal and cubic phas es, which are the most important ones for applications. Different methods f or the synthesis of powders (coprecipitation, amorphous citrate process, so l-gel, polymerised complex method and gel-combustion) and for the preparati on of ceramics are discussed. The equilibrium phase diagrams of the most co mmonly studied zirconia-based binary systems (ZrO2-Y2O3; ZrO2-MgO; ZrO2-CaO and ZrO2-CeO2) are considered and the domains of existence of the tetragon al 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 soli d solutions (such as ZrO2-Y2O3; ZrO2-Er2O3; ZrO2-Nd2O3; ZrO2-Sm2O3; ZrO2-Yb 2O3; 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 detai l.