Physical properties of mixed crystals of alkali halides

Abstract

The physical properties of mixed crystals of alkali halides are reviewed. The properties considered are experimentally determined quantities like the lattice constants, the compressibility, the elastic constants, thermal expansion, specific heats, Debye-Waller factors, dielectric constant, refractive index, IR spectra and Raman spectra and also some calculated solid-state parameters like Debye temperatures and lattice energies. A critical analysis of composition dependence shows four groups designated as follows: Type A, properties which vary linearly with composition; Type B, properties which vary slightly non-linearly with composition; Type C, properties which depend highly non-linearly on composition with the values for mixed crystals exceeding the values for end members; and Type D, properties which are peculiar to the mixed crystals and are not shown by the parent crystals. Most of the physical properties belong to Types A or B. Variation of Type C is shown only by properties affected by differences in ion size like the Debye-Waller factor and the microhardness. Properties which are symmetry-dependent like the first-order Raman spectrum and the IR spectra are of Type D. Attention is drawn to areas where further work is needed.