Impedance spectroscopy study of a compositionally graded lead zirconate titanate structure

The dielectric response of a compositionally graded lead zirconate titanate (PZT) structure prepared by pulsed laser deposition was studied as a function of frequency and temperature (from room temperature up to 419 degrees C) using impedance spectroscopy. The analysis of combined impedance and modulus spectroscopy, as well as complex plane plots, revealed that the bulk grain relaxation was the dominant relaxation process over the frequency and temperature range studied. The calculated bulk grain capacitance of the graded structure shows an anomalous behavior near temperatures related to the phase transition temperatures of the corresponding PZT compositions. The hopping conduction obeying the "universal power law" and an exponent equal to 0.88 was observed to dominate in alternating current conductivity over the entire frequency range from 10 Hz to 2 MHz at room temperature. At higher temperatures the relaxation spectrum was found to be much influenced by the increased direct current (dc) conductivity. The measured low frequency conductivity and the bulk grain dc conductance, calculated from impedance analysis indicate nearly the same Arrhenius-type thermally activated process with activation energies of 1.09 and 1.12 eV, respectively. These values were found to be in excellent agreement with those published in literature for perovskite ferroelectrics and may be attributed to motion of oxygen vacancies or field-enhanced emission of carriers from traps within the bulk. (c) 2007 American Institute of Physics.