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 the 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.