Phonons in Ta-D and Ta-H alloys

The acoustical phonon frequencies for Ta alloyed with 22% D and with 18% H have been measured at room temperature. For comparison the phonon dispersion curves of pure Ta (including previously unknown [110] T1 mode) have also been determined. The observed frequency shifts are qualitatively the same as those for the system Nb-D. For the optical branches in Ta-D two energy levels could be found at 20.3 THz and at 28.5 THz independent of the phonon wavevector. (author)