Study of the Wurtzite-Type Binary Compounds. II. Macroscopic Theory of the Distortion and Polarization

Abstract

The slight departure of wurtzite‐type binary compounds from ideal c/a ratio and ideal sublattice displacement parameter u is accounted for by the forces arising from partial polar binding. These long‐range forces are calculated in terms of a postulated charge ±fe per ion and certain lattice sums which we evaluate. When balanced against the elastic, piezoelectric, and dielectric constants of the crystal, the forces account for both the direction and the order of magnitude of the distortion. The compounds AlN, BeO, and ZnO are considered in detail. An experimental value of 8.5 is given for the dielectric constant of AlN, but in the absence of precise values for elastic and piezoelectric constants only an order of magnitude check of the theory can be made at this time. Some remarks are appended on the general problem of finite lattice sums in complex lattices which have dipole and/or quadrupole moments in the unit cell.