General behavior of longitudinal optical phonons in cubic diatomic crystals

A general relationship for longitudinal optical (LO) phonons in diatomic cubic crystals is introduced. The analysis of spectroscopic data of diatomic cubic crystals reveals that LO frequencies correlate directly with bulk moduli in a nearest-neighbor fashion. The proportionality constant is found to be dependent only on lattice geometries. Transverse effective charges can be obtained when the Lyddane–Sachs–Teller is incorporated into the model. Our calculations are in excellent agreement with experimental values and theoretical calculations. Some interesting implications of the model are discussed.