Microwave dielectric dispersion and the soft mode in ferroelectric PbHPO4

Abstract
The complex dielectric function epsilon ( omega ) along the a axis of PbHPO4 crystals is determined between 0.3 and 10 GHz by time-domain spectroscopy in the paraelectric and ferroelectric phase near the transition temperature Tc=309K. The main component of the dielectric dispersion mechanism related to proton ordering is found to be located in this frequency region. Analysis of the data in the paraelectric phase leads to the conclusion that the dielectric mechanism is a heavily damped soft mode with a frequency-dependent damping function.