Relaxor Behaviour in Pb(Fe0.5Nb0.5)O3

The relaxor, ferroelectric lead iron niobate, Pb(Fe_0.5Nb_0.5)O₃ (PFN) is synthesized by Coulombite precursor method. Scanning electron micrograph taken at room temperature shows the compactness of the sample. The average grain size is found to be ∼2 μm. The field dependence of dielectric response is measured in a frequency range, 0.1 kHz-1 MHz and in a temperature range from 27°C to 200°C. The temperature dependence of permittivity (ε^') shows broad maxima at various frequencies. The frequency dependence of the permittivity maximum temperature (T_m) has been modeled using Vogel-Fulcher relation. Cole-Cole plot confirms the polydispersive nature of the relaxation time. It is proposed that the deviation from Debye behaviour is a result of the development of correlations between polar moments leading to the onset of non-ergodicity near freezing. The results also show that at T > T_m , (1/ε^'-1/ε^'_m) is proportional to the exponent γ and is found to be 1.844 at both 253 and 304 kHz.