Decisive role of mixed-valence structure in colossal dielectric constant of LaFeO3

Abstract

The role of mixed-valence structure in colossal dielectric constant (CDC) behavior has been investigated in LaFeO 3 ceramics by tuning the ratio of Fe 2+ /Fe 3+ through substituting Al for Fe. The ratio of Fe 2+ /Fe 3+ is decreased gradually from 1.0 to 0.0 by increasing the concentration of Al 3+ . Two clear-cut correlations have been found: (i) the relationship between the CDC behavior and the ratio of Fe 2+ /Fe 3+ follows an exponential function and (ii) the activation energy of the polaron relaxation is proportional to 1/? 2 0 , where ? 0 is the intrinsic dielectric constant. These findings underscore the role of the mixed-valence structure in CDC behavior and suggest that adjusting the mixed-valence structure through doping/alloying can be a promising strategy to achieve superior CDC behavior in transition-metal oxides.