Advanced zirconia ceramics stabilized with yttria and magnesia: Structure and Vickers microhardness

The samples 8YSZ containing 70, 75, 80 mol% ZrO₂ and other oxides were prepared by. a high temperature solid state reaction process. Using X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and spectroscopic methods were evaluated the effect of oxide addition on the properties of yttria-doped zirconia. X-ray data shows the formation of zirconia (Y-doped), YSZ and/or tetragonal zirconia crystalline phases in all samples. IR data indicate the stretching vibrations of the Si-O bonds from tetrahedral [SiO₄] units and the stretching vibrations of the Fe-O bonds from [FeO₆] structural units, respectively. EPR results indicate the destroying of the local ordering of the Fe⁺³ ion vicinities situated in the rhombic distorted octahedral geometries by the increasing of ZrO₂ content in the host ceramic. The highest values of Vickers hardness were recorded for the ceramics containing 70 and 75 mol% ZrO₂. This superior performance can be explained considering the presence of a smaller amount of monoclinic ZrO₂ crystalline phase in the ceramic structure. The analysis of the X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) data shows the presence of Fe⁺² and Fe⁺³ ions. In the ceramics with higher ZrO₂ contents the iron atoms adopt a randomly structure due to the highly distorted [FeO₆] structural units and non-equivalent Fe-O distances in the first coordination shell.