Dielectric and electrical properties of 2/3Pb(Mg1/3Nb2/3)O3-1/3PbTiO3:CoFe1.97RE0.03O4 (RE = La3+ and Eu3+) composites

In this study, the dielectric and electrical properties of RE3+ substituted (1-x)2/3Pb(Mg1/3Nb2/3)O-3-xCoFe(1.97) RE0.03O4 (RE = La3+ and Eu3+) particulate composites (with x = 10, 15, 20, and 30 mol %) synthesized via a solid-state approach have been presented. The temperature-dependent dielectric constant epsilon' (T) displays a prominent peak around 180-190 ?, which drifts towards the high-temperature side with increasing frequency, consistent with the diffuse phase transition from ferroelectric to paraelectric. The high dielectric constant (epsilon') value and additional peak at the higher tempera-ture side are more prominent in CoFe1.97Eu0.03O4 (CFEO) than CoFe1.97La0.03O4 (CFLO) based composites because of the high conductivity of CFEO than CFLO. It is also seen that CFLO-based composite has much lower loss than CFEO-based composite owing to the lower conductivity of CFLO. The magnitude of dielectric loss (tan delta) increases with the tempera-ture and concentration of ferrites, which might be due to the occurrence of thermally active carrier hopping conductions in low-resistive ferrites. The Jonscher's double power law is used to analyse frequency-dependent AC conductivity. The temperature-dependent power exponents confirm that the conduction arises due to the transitional hopping of polarons. The complex impedance spectroscopy data modelled using equivalent electrical circuits show a single semicircle for both sets of composites, indicating that the conduction mechanism is only due to thermally active conducting grains.