Intragrain electrical inhomogenities and compositional variation of static dielectric constant in LaMn_{1-x}Fe_xO_3

TL;DR

This study investigates how Fe substitution affects the dielectric and electrical properties of LaMn_{1-x}Fe_xO_3, revealing compositional and structural influences on dielectric constant and resistivity, with evidence of intragrain inhomogeneities.

Contribution

It provides new insights into the relationship between Fe content, structural changes, and dielectric behavior in LaMn_{1-x}Fe_xO_3, including effects of oxygen annealing.

Findings

Dielectric constant epsilon_s peaks at x=0.5 and drops sharply at x=0.70.

Oxygen annealing increases epsilon_s significantly for x <= 0.50.

Electrical inhomogeneities are observed within the grain interiors.

Abstract

Bulk dc resistivity and dielectric constant measurements with temperature and frequency have been performed in LaMn_{1-x}Fe_xO_3 (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 (epsilon_s) at low temperature for x >= 0.15 where epsilon_0 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 epsilon_s at x = 0.70 is correlated with the structural change from rhombohedral to orthorhombic structure. A considerable increase of epsilon_s ~ 43% is observed for an increase of x from 0.15 to 0.50. Furthermore, epsilon_s 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 epsilon_s 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.