ABSTRACT
This work involves the synthesis and study of physical properties of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound, which has been characterized by various experimental techniques, such as X-ray diffraction, SEM and complex impedance spectroscopy. The structural study showed that the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound crystallized in the orthorhombic structure with the Pnma space group. The particle size and the surface morphology of this compound have been analysed using SEM. The particle size was found to be around 120 nm and we confirmed that one particle contains more than one crystallite. Importantly, the studied compound presented a giant dielectric permittivity (ε' of around 9 × 104 at high temperature and low frequencies). An equivalent electric circuit has been deduced from the Nyquist plots of the complex impedance parts (Z'' vs. Z') to correctly describe the electrical behavior of the La0.8Ca0.1Pb0.1Fe0.975Mg0.025O3 compound. The chosen circuit consists of two cells mounted in series corresponding to the grain and grain boundary contributions. The electrode contribution has been detected from the frequency dependence of the imaginary part of modulus where the activation energy of each constitution has been calculated. The relaxation process and the electrical conductivity are attributed to the same type of charge carriers characterized by similar values of the activation energy determined from loss factor tangent (tg(δ)), the imaginary part of the permittivity and the modulus spectrum.
ABSTRACT
(La0.8Ca0.2)1-x Bi x FeO3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) (LCBFO) multiferroic compounds have been prepared by the sol-gel method and calcined at 800 °C. X-ray diffraction results have shown that all samples crystallise in the orthorhombic structure with the Pnma space group. Electrical and dielectric characterizations of the synthesized materials have been performed using complex impedance spectroscopy techniques in the frequency range from 100 Hz to 1 MHz and in a temperature range from 170 to 300 K. The ac-conductivity spectra have been analysed using Jonscher's power law σ(ω) = σ dc + Aω s , where the power law exponent (s) increases with the temperature. The imaginary part of the complex impedance (Z'') was found to be frequency dependent and shows relaxation peaks that move towards higher frequencies with the increase of the temperature. The relaxation activation energy deduced from the Z'' vs. frequency plots was similar to the conduction activation energy obtained from the conductivity. Hence, the relaxation process and the conduction mechanism may be attributed to the same type of charge carriers. The Nyquist plots (Z'' vs. Z') at different temperatures revealed the appearance of two semi-circular arcs corresponding to grain and grain boundary contributions.
