Impedance Spectroscopy Study in the vicinity of Ferroelectric Phase   Transition
  An impedance spectroscopy (IS) is a versatile tool to study the effect of grains (bulk), grain boundaries and electrode-electrolyte interface on dielectric and electrical properties of electro-ceramics. This study only focuses the high frequency (1 kHz to 10 MHz) probe of bulk ferroelectric capacitance near ferroelectric phase transition temperature (FPTT). The PZTFW single phase and PZTFW-CFO composites, respectively, have been investigated to understand the microstructure-property relation. Keeping in mind the complex microstructure of both systems, low frequency ( less than 1 kHZ ) impedance investigation, which basically deals with grain boundaries and electrode-interfaces, has been ignored. X-ray diffraction (XRD) patterns, microstructures, dielectric spectra, and impedance plots revealed two distinct phases, inbuilt compressive strain, small shift in dielectric maximum temperature, and two activation energy regions, respectively, in PZTFW-CFO composite compare to PZTFW ceramic. Addition of CFO in PZTFW medium purified the impurity phases present in the PZTFW matrix. The PZTFW-CFO composite shows flat dielectric behavior and high dielectric constant near FPTT at high frequency may be useful for tunable dielectric capacitors. The changes in bulk capacitance, relaxation time and constant phase element parameters have probed in the proximity of FPTT regions. Nyquist plot and modulus formalism show a poly-dispersive nature of relaxation, relate the activation energy (Ea) of oxygen vacancies, mainly responsible for the bulk capacitive conduction. A spiral kind of modulus spectra was observed at elevated temperatures and frequencies (greater than 2 MHz) suggests the possible experimental artifacts, have no physical reasons to explain. 
Hitesh Borkar, M Tomar, Vinay Gupta, and Ashok Kumar
cond-mat.mtrl-sci