Dielectric response of some ferroelectrics at ‘low’ frequencies I

The dielectric response of ferroelectric PST ceramics and of TGS single crystals was measured in the seldom reported range 10−3-104 Hz. Their complex dielectric susceptance (ω) = X′(ω)—iX″(ω) shows, after removal of processes such as direct-current conductivity, Low-Frequency Dispersion and certain dipolar features, underlying regions of relatively ‘flat’ frequency dependence obeying the ‘universal’ fractional power laws u (ω) ∝ (iω n-1) extending over five to seven decades of frequency. The magnitude of the power-law exponent n depends weakly on temperature and on the magnitude of the permittivity and depends only slightly, if at all, on the ferro- or para-electric state of the sample. We note that this residual universal response is seen by us more clearly in ferroelectric materials than in any others. The significance of these results is discussed.