LATTICE-DYNAMICS AND RELATED DIFFUSION PROPERTIES OF INTERMETALLICS .2. NI3SB

The phonon dispersion of the intermetallic Ni72.5Si27.5 has been studi ed by inelastic neutron scattering in its high-temperature phase of DO 3 structure, stable above 530 degrees C. The dispersion has been exami ned at a temperature of 600 degrees C; some selected branches were als o studied at 530 degrees C (i.e. very close to the phase transition) a nd at 900 degrees C. In general, the phonons are very strongly damped and some branches have not been found at all. For transverse phonons w ith [xi xi 0] propagation, the frequency does not change as a function of the temperature, but the widths become larger towards higher tempe ratures. The migration enthalpy and several other thermodynamic quanti ties have been calculated from the densities of states. The anomalous behaviour of the alloy is related to high vacancy densities.