Martensitic transformation of KAI₄: Evidence of a displacive origin

Abstract

We report on the first inelastic neutron scattering investigations of the layer material KAIF₄ which undergoes a martensitic phase transition. It is shown that the transition is preceeded by the softening of a flat phonon branch. The atomic displacements corresponding to these phonons are determined by a rigid ion model; a mechanism has been proposed to explain how the martensitic transition can be related to the phonon softening.