Correlation of La-mediated structural transition and dielectric relaxation in Bi2Mg2/3Nb4/3O7 pyrochlores

Bismuth based pyrochlores have attracted a massive interest in the modern research areas owing to their structural tenability and variety of physical properties. The structural variation and its consequent effects on dielectric relaxation have been presented in this work by synthesizing a series of La-mediated Bi2-xLaxMg2/3Nb4/3O7 (x = 0.00, 0.05, 0.10, 0.15, 0.20 and 0.25) ceramics using sol-gel auto-combustion technique. Coexistence of fluorite and cubic pyrochlore phases in the parent composition and gradual enrichment of pyrochlore phase with increase of substitution contents was observed from the structural analysis. Distortion of spherical symmetry of grains with reduced grain size from 950 to 500 nm was revealed by field emission scanning electron microscope. The presence of required constituent elements with their correct proportion was analysed using energy dispersive X-ray spectroscopy. Complex impedance study and frequency dependent dielectric dispersion analysis was performed to check ac-conductivity and to explore potential of material for energy storage applications. With the help of complex modulus analysis, the range of carrier transportation inside the material was distinguished in different frequency regimes.