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

The formation behavior of Y2O3 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 Ia3, a=10.58 Å) to the metastable B-type monoclinic (space group C2/m, a=13.89 Å), 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 Y2O3 at a nanoscale smaller than 10 nm is possible by forming metastable monoclinic crystals, which are strain-induced. - Graphical abstract: The fig shows the solid-state phase formation of Y2O3 by very high energy input into the particles during milling: ordered body-centered cubic phase (space group Ia3, a=10.58 Å) nanocrystalline monoclinic phase (space group C2/m, a=13.89 Å) disordered monoclinic phase partial amorphous phase. The formation of Y2O3 smaller than 10 nm was strongly dependent on whether the phase transition from cubic to monoclinic occurred. Highlights: ► This paper analyses very high energy milling behavior of coarse Y2O3 particles. ► A drastic phase transition from cubic to monoclinic occurred with a partial amorphization. ► An existence of Y2O3 smaller than 10 nm is possible by forming strain-induced monoclinic crystals