Anharmonic strain effects in crystals and mixed valence states

Abstract

We modify Friedel's discussion of the elastic model of alloys by showing that "impurities" of different sizes can attract each other when the strains involved are very large. This fact has applications in various physical phenomena. An example is the metal-insulator transitions of SmS, SmSe, and SmTe under pressure. Our theory explains why the transition in SmS is much less continuous than that of SmSe and SmTe. Other applications are also discussed.