Inelastic and quasielastic neutron scattering study of the 1-D dynamics of K-Hollandite

Inelastic and quasielastic neutron scattering studies were carried out on a K-Hollandite sample composed of 25 single well oriented crystals. An anomalous behaviour of a TA-Λ3/4-dispersion branch along (00ζ) was observed. Above ζ about 0.21 the branch becomes unobservable in the Brillouin zones investigated so far and deviated from a 'normal' behaviour in the range 0.15 < ζ < 0.21 with respect to energy width and integrated intensity. Weak but distinct scattering occurs within the Q,ω-plane around/above ζ about 0.21. It seems to be plausible that this is due to a framework distortion around empty cavities along the K+-chains. No clear evidence for an interaction between a bottle-neck mode and a 1-d motion of the K+-ions was found. Remarkable quasielastic scattering - as predicted by theoretical work based on a FK-model - was observed and gross features may be reproduced. A better agreement, however, is achieved with a simple damped harmonic oscillator model. (author) 5 refs., 7 figs