Investigation of dielectric and electrical behavior in Pb(Fe_(0.66)W_(0.33))_(0.50)Ti_(0.50)O_3 thin films by impedance spectroscopy

摘要

We have synthesized polycrystalline (1 - x)Pb(Fe_(2/3)W_(1/3))O_3-xPbTiO_3 (x=0.50) (PFWT) thin films on Pt/Ti/SiO_2/Si(100) substrates by chemical solution deposition technique. X-ray diffraction patterns indicate tetragonal crystal structure at room temperature. The dielectric spectroscopy studies in these films were carried out in the temperature range of 300-650 K, over a wide range of frequency (100 Hz to 1 MHz) indicates polydispersive nature of the materials. Real and imaginary parts of the dielectric constant indicated strong frequency dispersion in the low-frequency region suggest development of space charge at elevated temperature. The ferroelectric phase transition was found at 575 K (Curie temperature) for all frequencies, as is evident from the temperature dependent dielectric constant. The degree of relaxation coefficient (gamma approx 1.30) was estimated from a linear fit of the modified Curie-Weiss law and the results suggested a long-range ordering. The impedance spectroscopy suggests two different relaxation mechanisms in the materials below and above the Curie temperature. A significant shift in impedance loss peak towards higher frequency side near the ferroelectric phase transition indicates that the grain started conducting and favoring the long-range motion of mobile charge carriers. The master modulus spectra revealed that grain and grain boundary capacitance plays a crucial role in conduction mechanism above the Curie temperature. The ac conductivity well behaves the Jonscher's power law and the hopping frequency shifted towards higher temperature side with increase in temperature that indicates frequency independent conductivity above Curie temperature.