Characterization of Cubic and Monoclinic Phases in Ball-Milled Nanocrystalline-Y2O3 Using Experimental and Simulated Oxygen K-Edge Positions in STEM-EELS

Abstract Yttria (Y 2 O 3 ) is a refractory ceramic of great technological importance. The material with a stable cubic crystal structure transforms into a monoclinic phase when ball-milled under specific conditions. The synthesis methodology can be engineered to have mixed phase (cubic + monoclinic) Y 2 O 3 . Scanning transmission electron microscopy (STEM)-based electron energy-loss spectroscopy (EELS) is an elegant method to characterize these phases. This paper provides an experimental methodology to use the electron energy-loss near-edge structure (ELNES) of oxygen (O) K-edge as a fingerprint to uniquely identify the phases. The spectrum so obtained was corroborated with simulated patterns. The distortion of the octahedral network of O in the cubic-Y 2 O 3 structure crafts a monoclinic structure and this is manifested as a reduction in peak separation (ΔE) at the O K 1 and K 2 —edges as compared to the same for the higher symmetry cubic structure. The unique insight provided by the O K-edge EELS is discussed in the context of phase identification and may be extended to rare-earth oxide polymorphs. Graphical Abstract