Trends in the Characteristic Phonon Frequencies of the NaCl-, Diamond-, Zinc-Blende-, and Wurtzite-Type Crystals

Abstract

Several correlations are noted among the characteristic phonon frequencies of the I—VII, II—VI, III—V, and IV—IV compounds. In particular, the following linear relations are established: (1) between the Szigeti effective ionic charge q* and the zone center optical phonon separation (ν1—νt)/νt for the II—VI and III—V compounds; (2) between νt2 and ν12, and the reciprocal reduced mass 1/μ for the II—VI and III—V compounds, between νt2 and a/χμ, in the case of the alkali halides where a and χ are the lattice constant and compressibility, respectively; (3) between χ and an where n=4 for the zinc blende and n=3 for the alkali halides; and (4) between q* and α——α+, the difference between the atomic polarizability of the II—VI and III—V compounds. Comparison of observed and calculated compressibilities reveals that the Brout and Szigeti relations are more applicable to the IV—IV and III—V compounds, and to a lesser degree to the II—VI compounds, than to the alkali halides for which they were originally proposed.