Lattice Vibrations and Incommensurate Phase Transitions in K2SeO4, Rb2ZnCl4 and K2ZnCl4

P. ECHEGUT; G. HAURET; F. GERVAIS; NESTOR E. MASSA

Jpn. Journal of Applied Physics

IOP Publishing

Lugar: Bristol; Año: 1985 vol. 24 p. 778 - 780

The temperature dependence of the dielectric function of K2ZnCl4 deduced from infrared reflection spectra is reported over the PE, INC, and FE phases. Whereas differences in the transition mechanism at Ti between K2SeO4 and K2ZnCl4 and Rb2ZnCl4 are recognized, the origin of the dielectric constant anomalies at Ti and Tc are discussed within the context of a same model in particular the lock-in transition in understood as an instability of the lattice against correlated discommensuration sliding fluctuations. In the INC phase, the spectra of the three compounds show the increase of additional modes. Their number is compatible with incipient tripling of the PE unit cell along the pseudo-hexagonal axis. No additional mode is observed in the FE phase and no significant change of regime occurs around Tc in the temperature dependence of mode intensities.