Frequency-dependent electrical properties of ferroelectric BaTi2O5 single crystal.

Analysis and modeling of impedance spectroscopy data of ferroelectric BaTi2O5 single crystal has been carried out at temperatures both below and above the ferroelectric Curie temperature, TC. 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 TC, the resistance R is too large to measure and the circuit simplifies to C-CPE. Above TC, 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, TC∼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 TC, 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. [ABSTRACT FROM AUTHOR]