Experimental evidence for lattice instability of potassium at low temperatures

Abstract
Experimental evidence is presented for a tendency towards a lattice instability in potassium at low temperatures by neutron scattering techniques. The main result is the observation of a Huang diffuse scattering below 70 K in the vicinity of the (110) and (220) bcc Bragg reflections. Furthermore, the transverse-acoustic-phonon branch in the [110] direction with polarization [110] shows a softening of a few percent between 100 and 4 K, similar to Na and Li.