Effective charges in binary and ternary oxide compounds

Effective charges in non-cubic binary oxide crystals are evaluated on the basis of their transverse and longitudinal optical phonon frequencies. The temperature dependence of the effective charge is reported in quartz, rutile and corundum. Three procedures which allow the determination of effective charges in ternary compounds are presented and applied to halogenate, silicate, aluminate and ABO_n-type crystals, where A is an alkali or alkaline earth and B is a transition-metal element. Results are compared with Phillips's ionicities.