Anomalous Behavior of the Dielectric and Pyroelectric Responses of Ferroelectric Fine-Grained Ceramics

We revealed the anomalous temperature behavior of the giant dielectric permittivity and unusual frequency dependences of the pyroelectric response of the fine-grained ceramics prepared by the spark plasma sintering of the ferroelectric BaTiO3 nanoparticles. The temperature dependences of the electro-resistivity indicate the frequency-dependent transition in the electro-transport mechanisms between the lower and higher conductivity states accompanied by the maximum in the temperature dependence of the loss angle tangent. The pyroelectric thermal-wave probing revealed the existence of the spatially inhomogeneous counter-polarized ferroelectric state at the opposite surfaces of the ceramic sample. We described the temperature behavior of the giant dielectric response and losses using the core-shell model for ceramic grains, effective medium approach and Maxwell-Wagner approach. The superparaelectric-like state with a giant dielectric response may appear due to the internal barrier-layer capacitance effect, while the step-like thermal activation of localized polarons in the semiconducting grains is not excluded. The elucidation of the state microscopic origin requires measurements in the frequency range above 1 MHz.