Doroshenko A. Morphological and phase stability of Y2O3:Eu3+ and Y3Al5O12 nanopowders consolidated at high pressures.

Thesis is devoted to study the structure, phase composition and properties of Y2O3:Eu3+ and Y3Al5O12 nanopowders and compact nanomaterials on their basis obtained at the pressures of 4 8 GPa. The synthesis conditions of 60 nm weakly-agglomerated Y3Al5O12 nanopowders by co-precipitation method have been determined. Electrostatic stabilization by sulfate-ions allows one to lower agglomeration degree of Y3Al5O12 nanopowders, as well as to increase their sintering activity in comparison with non-stabilized nanopowders. The formation conditions of highly-loaded water suspensions of Y3Al5O12 nanopowders have been determined. Y3Al5O12 compacts with green density up to 54 % have been obtained by slip casting. High-density ( ?99 %) Y3Al5O12 compact nanomaterials with 20 40 nm grain size have been obtained by high-pressure consolidation of nanopowders at Р=8 GPa, Т=350 450°С. Phase instability of 60 nm Y3Al5O12 nanopowders consolidated at P=8 GPa and T=550°С leads to decomposition of garnet phase into YAlO3 and Al2O3. The influence of real structure of Y3Al5O12 nanomaterials on their luminescent properties has been studied. The consolidation parameters to obtain fully dense Y2O3:Eu3+ nanoceramics with 10 15 nm grain size by transformation-assisted consolidation of nanospheres at high pressures have been determined. Consolidation at P=8 GPa allows one to lower formation temperature of Y2O3:Eu3+ translucent nanoceramics by order of magnitude compared to conventional methods due to essential activation of a plastic flow during cubic-to-monoclinic phase transition of Y2O3.