Dynamical properties of copper halides. I. Interionic forces, charges, and phonon dispersion curves

In the three papers in this series the anomalous dynamical properties of copper halides are analyzed. The present paper focuses on the interionic forces and phonons in these materials. It is shown that the partially ionic nature of these tetrahedrally coordinated semiconductors is best described by various valence-shell models which combine a valence-force-field approach with that of dipolar models (i.e., effective charge, polarizabilities, etc.). The trends of the interionic forces in the sequence CuCl{→}CuBr{→}CuI reflect the changes in the electronic band structure and the increasing tendency to superionic conductivity.