CONSTANT Q-MEASUREMENTS OF COLLECTIVE MODES IN MG70ZN30 GLASS

In this study the neutron Brillouin scattering technique has been used to measure longitudinal excitations in a magnesium-zinc glass at mome ntum transfers within the first pseudo-Brillouin zone. The measurement s were performed at room temperature and constant momentum transfer, w hich enables the data to be readily and reliably compared with theory. The experimental results taken down to Q = 6.2 nm(-1) and E = 27 meV show a 5 meV downward shift in the dispersion energy of the longitudin al 'optic' mode of the glass when compared to theoretical predictions. (C) 1998 Elsevier Science B.V. All rights reserved.