Effect of valence fluctuations on lattice vibrations

Abstract

The effect of valence fluctuations on various phonon modes are studied theoretically. It is shown that for a system like SmS the valence fluctuations may cause a softening of the longitudinal optical phonons which should be observable. For Sm1-xYxS the atomic displacements of only S ions, not of the Sm ions increase upon approaching the transition temperature at which the smooth transition from the golden metallic phase to the black semiconducting-like phase occurs. Furthermore, the authors discuss how acoustic phonons are affected by the valence transition.