Structural Nature of Polyamorphism in Y 2 O 3 –Al 2 O 3 Glasses

The structural attributes of the polyamorphic high- and low-density amorphous phases in Y 2 O 3 –Al 2 O 3 glasses with 24–41 mol % Y 2 O 3 have been investigated using high-resolution 27 Al and 89 Y 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.