Structural Nature of Polyamorphism in Y₂O₃–Al₂O₃ Glasses

Abstract

The structural attributes of the polyamorphic high- and low-density amorphous phases in Y2O3–Al2O3 glasses with 24–41 mol % Y2O3 have been investigated using high-resolution 27Al and 89Y nuclear magnetic resonance spectroscopy in combination with back-scattered electron and transmission electron microscopy imaging and differential scanning calorimetric measurements. Glasses over the entire composition range are characterized by a uniform dispersion of droplets of one phase in the matrix of the other phase resulting from a density-driven phase separation in the supercooled liquid state. Although compositionally identical, the structures of the two phases differ primarily in their Y coordination environment and in the structural order associated with the connectivity and packing of the Al–O and Y–O coordination polyhedra. It appears that, compared to the matrix phase, the droplet phase is characterized by a significantly higher degree of short-range structural order.