On the lattice dynamics of hcp hafnium

We measured the phonon dispersion curves of hcp Hf at 295, 800, and 1300 K. We find that (unlike the other modes) the zone center 001]LO mode softens appreciably as the temperature decreases and at room temperature this branch exhibits a dip at the zone center. This anomalous behavior is similar to that observed in hcp Zr, Ti, and Tc and seems to be characteristic of the hcp superconducting elements.