Control of Y2O3 phase and its nanostructure formation through a very high energy mechanical milling

Abstract The formation behavior of Y 2 O 3 ceramic particles was studied by employing a very high energy ball milling (milling energy: ∼165 kJ/g·hit, milling speed: 1000 rpm). Both the XRD and HRTEM studies revealed that the high impact strain energy generated during the milling caused a drastic phase transition from the original C-type cubic (space group Ia 3, a =10.58 A) to the metastable B-type monoclinic (space group C 2/ m , a =13.89 A), finally followed by a partial solid-state amorphization. The cubic phase was difficult to be reduced down to smaller than 10 nm, while the monoclinic phase was stabilized at sizes smaller than 10 nm with a mean crystallite size of 7.57 nm. Consequently, the existence of Y 2 O 3 at a nanoscale smaller than 10 nm is possible by forming metastable monoclinic crystals, which are strain-induced.