Dynamics at the ferroelectric to dipolar glass transition

Abstract

Abstract We review our measurements on the polarization dynamics near the dipolar glass transition in KTN, at low niobium concentration (0.9-1.2%). Measurements over a wide range of characteristic times, including Raman and Neutron scattering, Brillouin scattering, ac dielectric response, and polarization decay, have revealed the presence of relaxation processes which vary over a very wide time range as the low concentration sample is cooled. At the higher concentration (1.2%) this behavior changes somewhat, showing evidence for the development of two transitions, at temperatures of about 15 K and 19-20 K, respectively. The dynamic signatures of the two transitions are different. The upper transition is characterized by a low frequency soft mode which exhibits a minimum in frequency as a function of temperature, but no evidence has been found for development of long-range ferroelectric order. The lower transition exhibits a divergent and singular central peak phenomenon. We speculate as to the origin of this pair of transitions.