Intragrain electrical inhomogenities and compositional variation of static dielectric constant in LaMn1-xFexO3
Abstract
Bulk dc resistivity and dielectric constant measurements with temperature and frequency have been performed in LaMn1-xFexO3 (0 <= x <= 1.0) as a result of Fe substitution both for the as-synthesized and oxygen annealed samples. Temperature dependence of real part of dielectric constant at different frequencies show a frequency and temperature independent value (epsilons) at low temperature for x >= 0.15 where epsilon0 rises with x reaching a maximum at x = 0.5 and then it decreases sharply at x = 0.70 showing a further increasing trend with the further increase in x. The sharp drop of epsilons at x = 0.70 is correlated with the structural change from rhombohedral to orthorhombic structure. A considerable increase of epsilons ~ 43% is observed for an increase of x from 0.15 to 0.50. Furthermore, epsilons is increased considerably (up to ~ 17% at x = 0.5) due to the oxygen annealing for x <= 0.50. The low temperature resistivities satisfying Variable Range Hopping model are found to be related with the increase of epsilons with x for x <= 0.50. The analysis of the complex impedance and modulus planes at low temperature indicates the electrical inhomogeneities in the grain interior of the compounds.