Structural transformations on vitrification in the fragile glass-forming system CaAl2O4.
The structure of the fragile glass-forming material CaAl(2)O(4) was measured by applying the method of neutron diffraction with Ca isotope substitution to the laser-heated aerodynamically levitated liquid at 1973(30) K and to the glass at 300(1) K. The results, interpreted with the aid of molecular dynamics simulations, reveal key structural modifications on multiple length scales. Specifically, there is a reorganization on quenching that leads to an almost complete breakdown of the AlO(5) polyhedra and threefold coordinated oxygen atoms present in the liquid, and to their replacement by a predominantly corner-sharing network of AlO(4) tetrahedra in the glass. This process is accompanied by the formation of branched chains of edge and face-sharing Ca-centered polyhedra that give cationic ordering on an intermediate length scale, where the measured coordination number for O around Ca is 6.0(2) for the liquid and 6.4(2) for the glass.
Centre for Science at Extreme Conditions, School of Physics and Astronomy, University of Edinburgh, Edinburgh EH9 3JZ, United Kingdom. james.drewitt@ed.ac.uk
James W E
JW
Drewitt
Louis
L
Hennet
Anita
A
Zeidler
Sandro
S
Jahn
Philip S
PS
Salmon
Daniel R
DR
Neuville
Henry E
HE
Fischer