Raman scattering of mixed K1-xNaxCl crystals

Raman scattering for NaxK1-xCl single crystals with 12 different Na concentrations x has been measured at 300 and 10 K. The cationic-disorder-induced Raman effect in the one-phonon region 0-200 cm-1 has been experimentally analysed in terms of spectral structure, symmetry and relative strength as a function of Na concentration x. For low concentrations (3-6%) of Na+ or K+ single defects or defect pairs, theoretical calculations have been performed based on the semi-classical off-resonance theory with a Green function-breathing shell model approach in the average T-matrix approximation. The agreement between calculated and experimental spectra can be considerably improved by basing the model on inter-ionic (rather than intra-ionic) polarisability and by extending coupling and force-constant changes beyond the first to second and fourth neighbours of the defect. Some serious discrepancies, however, remain unresolved.