Intragrain electrical inhomogenities and compositional variation of static dielectric constant in LaMn1-xFexO3

摘要

Bulk dc resistivity and dielectric constant measurements at different temperatures and frequencies have been performed in LaMn1-xFexO3 (0 <= x <= 1.0) as a result of Fe substitution both for as-synthesized and oxygen annealed samples. Temperature dependence of the real part of the dielectric constant at different frequencies show a frequency and temperature independent value (epsilon(S)) at low temperature for x >= 0.15 where epsilon(S) rises with x reaching a maximum at x = 0.5 and then decreases sharply at x = 0.70 showing a further increasing trend with a further increase in x. The sharp drop of epsilon(S) at x = 0.70 is correlated with the structural change from rhombohedral to the orthorhombic structure. A considerable increase in epsilon(S) similar to 43% is observed for an increase in x from 0.15 to 0.50. Furthermore, epsilon(S) is increased considerably (up to similar to 17% at x = 0.5) due to the oxygen annealing for x <= 0.50. The low temperature resistivities satisfying the variable range hopping model are found to be related to the increase in epsilon(S) with x for x <= 0.50. The analysis of the complex impedance and modulus (M) planes at low temperature indicates electrical inhomogeneities in the grain interior of the compounds where the capacitance obtained from the high-frequency complex-M arc shows an anomaly at the onset of the short range ferromagnetic ordering, suggesting a possible magnetoelectric coupling for x = 0.3.