APPLICIBALITY OF A RIGID-ION MODEL TO ZINC-BLENDE CRYSTALS

The applicability of the rigid-ion model to the phonon dispersion in zinc-blende type crystals is discussed. An invariance relation has been obtained connecting the elastic constants C11, C12 and C44 and the long wavelength longitudinal and transverse optic mode frequencies. This relation is found to apply well in the case of a number of II-VI and III-V compounds. An empirical relation connecting the ratio of the zone boundary (at X C.P.) LO and LA phonon frequencies with the mass ratios for diatomic cubic crystals is confirmed by the present model. The available neutron scattering and specific heat data on zinc-blende crystals is discussed in the light of the present model. © 1969.