Frequency-dependent electrical properties of ferroelectric BaTi₂ O₅ single crystal

Analysis and modeling of impedance spectroscopy data of ferroelectric BaTi₂ O₅ single crystal has been carried out at temperatures both below and above the ferroelectric Curie temperature, T _C. The most appropriate equivalent circuit is found to consist of a parallel combination of a resistor (R), capacitor (C), and constant phase element (CPE). Below T_C, the resistance R is too large to measure and the circuit simplifies to C-CPE. Above T_C, R shows Arrhenius behavior with low values of conductivity, eg ∼4× 10-7 S cm-1 at 800 K and high activation energy, 1.13(2) eV, and represents a thermally activated dc hopping process associated with leakage transport of either electrons or holes through the crystal lattice. C is frequency-independent, passes through a maximum at the ferroelectric-paraelectric transition temperature, T_C ∼475°C, represents the limiting high frequency capacitance of the crystal and is attributed to the response of the individual dipoles that are responsible for the ferroelectricity. The A parameter of the CPE also passes through a maximum at T_C, is not thermally activated in the same manner as R but shows similar temperature dependence to that of C. The physical origin of the CPE, with interlinked resistive and capacitive components, whose relative contributions are governed by the power law n parameter, may be associated with dipole-dipole interactions and reflect the time- and frequency-dependence of their cooperative nature.