  In this paper, impedance spectroscopy study was performed to establish the
electrical property and microstructure relations of the as-deposited and
post-annealed polycrystalline CCTO films prepared on Pt/Ti/SiO2/Si (100)
substrates by pulsed-laser deposition (PLD). Our results demonstrated that the
as-deposited polycrystalline CCTO film was made of insulating grain boundaries
with semiconducting grains, indicating that the high-dielectric-constant is
attributed to the barrier layer capacitor (BLC) effects. The simple
resistor-capacitor (RC) equivalent circuit and the modified constant phase
element (CPE) circuit were used to describe the impedance spectroscopy, and
excellent agreement between the calculated and measured curves was obtained in
the CPE circuit. The resistance and capacitance of the grains and grain
boundaries can be tuned by changing the annealing atmosphere and temperature.
Under oxygen-absent annealing atmosphere, the electric resistances of the grain
boundaries changed greatly but the resistance of the grains has almost no
change. While under oxygen annealing atmosphere, the reverse happened. On the
basis of this result, it is demonstrated that the origin of the
semiconductivity of the grains in CCTO polycrystalline films arises from their
oxygen-loss, while the grain boundaries are close to oxygen- stoicheometry.
