Neutron scattering investigation of lattice dynamics and thermally induced disorder in the antifluorite Mg2Si

Neutron scattering techniques have been used to investigate the temperature dependence of the lattice dynamics and fast ion behaviour of the antifluorite compound Mg2Si between 293 and 1313 K. The phonon energy dispersion relation has been measured at 293 K, and the data fitted by a shell model. The ionicity is determined to be circa 27%. Coherent diffuse scattering is observed which increases with temperature, indicating a thermally induced dynamic disorder of the Mg lattice. This involves slower fluctuations of disordered ions correlated over a longer range than that exhibited by ionic fluorite compounds close to their melting temperature. 14 refs.; 3 figs.; 1 table