Effect of sintering temperature on dielectric properties of Pb(Fe1/2Nb1/2)O-3 perovskite material

Lead iron niobate [Pb(Fe1/2Nb1/2)]O-3 (PFN) are synthesized by using precursor method. Three different sintering temperatures (1000, 1040 and 1100degreesC) are selected to optimize the PFN processing technique. X-ray powder diffraction studies confirm the formation of single-phase perovskite PFN. The scanning electron microscopy (SEM) study revealed increase in grain size with increasing sintering temperature. Quadrupole splitting observed in room temperature Mossbauer spectra for sample sintered at 1000degreesC disappears on sintering it at 1040 and 1100degreesC. The decrease in isomer shift with increasing temperature is attributed to change in oxidation states of Fe. The dielectric constant of these samples, measured in the frequency range (100 Hz to 1 MHz) and temperature range from 25-175degreesC, show giant values and diffuse phase transition behavior (DPT around 104.5degreesC). Although, the dielectric constant increases with increase in sintering temperature, however the transition temperature (104.5degreesC) is seen to be independent of frequency. Both these properties predict non-relaxor nature of PFN. High value of dielectric constant is interpreted on the basis of the formation of barrier at the interface of grain and grain-boundaries. High dielectric loss is understood to be due to hopping of electrons between Fe+2 to Fe+3.