THE EFFECTS OF INCOMMENSURABILITY ON THE PHONON MODES IN THE ONE-DIMENSIONAL SUPERIONIC CONDUCTOR K-HOLLANDITE

Polarized Raman and infrared spectra of the one dimensional (1-D) superionic conductor (K2xMgxTi(8-x)O16; x = 0.77) have been measured over the phonon frequency region 10-1000 cm-1 as a function of temperature and pressure. The majority of the IR and Raman active modes predicted by group theory for the (Ti, Mg)O6 framework were observed. The frequencies and their IR and Raman scattering cross-sections for the incommensurate lattice of K+ ions were calculated using a one dimensional linear chain model. This model assumes Coulomb interaction between nearest neighbors that are located in a sinusoidal potential due to the framework lattice. Several broad Raman bands were attributed to amplitudon type modes from the one dimensional incommensurate K+ ion sublattice. The IR active phason modes could not be identified unambiguously due to the underlying TiO framework vibrations which are known to possess large anharmonicity and oscillator strenghts. © 1985.