Yashchishyn I. The structure and surface state of ZrO2-Y2O3-Cr2O3 nanocrystals and mechanical properties of polycrystals based on them.

Thesis is focused on systematic investigation of chromium doping influence on the structure and surface state of ZrO2 - 3 mol. % Y2O3 nanocrystals along with physico-mechanical properties of ceramics based on these nanocrystals. The structure of nanoparticles near surface layer and hydrate shell was studied by several spectroscopic techniques, in particular by x-ray photoelectron spectroscopy. It is shown that chromium concentration in near surface layer of the nanoparticles rise and their hydrate shell inhomogeneously changes under chromium doping. These changes are cased by zirconium hydroxide composition change under chromium doping. The increase of chromium concentration in the near surface layer of the nanoparticles leads to the formation of composite ceramics based on ZrO2-Y2O3-Cr2O3 matrix and Cr2O3 inclusions with increased values of fracture toughness. Solubility limit of chromium in ZrO2 - 3 mol.% Y2O3 lattice is defined and the model of nanoparticles evolution from their origin to the formation of polycrystalline state is proposed.