FAR INFRARED AND MILLIMETER DIELECTRIC RESPONSE OF INCOMMENSURATE AND FERROELECTRIC K2SEO4

Dielectric response of K2SeO4 in the spectral region 5-460cm-1 was determined using transmissivity and reflectivity measurements as a function of temperature between 80 and 300K. The spectral features above 20cm-1 are interpreted using results of lattice vibrational analysis in three known commensurate phases. The low-frequency dielectric anomaly in the incommensurate phase can be roughly described by critical slowing-down of a Debye relaxation given rise to by the overdamped infrared active phason mode which softens at the incommensurate-commensurate transition. © 1979 Springer-Verlag.