Low-lying phonon dispersion curves of D0(3) Cu3Al(+Be)

The low-lying phonon dispersion curves of a DO3 ordered Cu3Al(+Be) shape-me mory alloy were measured, at room temperature, along the [xi 00], [xi xi 0] , [xi xi xi], [xi xi 1], and [1/2, 1/2, xi] symmetry directions. As in othe r bcc metals and alloys, we find that the frequencies of the TA(2)[xi xi 0] modes are relatively low and that the L[xi xi xi] branch exhibits a pronou nced dip at xi=2/3. The measured low-lying phonon dispersion curves are qui te similar to those of a bcc structure. Actually, a fifth-nearest-neighbor force constant bcc model provides a satisfactory fit to the low-lying phono n dispersion curves of this alloy. This model was used to evaluate the elas tic constants, the phonon density of states, and the lattice specific heat. The results of these calculations are in good agreement with macroscopic m easurements of the elastic constants and specific heat of this alloy. [S016 3-1829(99)02114-1].