Origin of the high permittivity in (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 ceramics

Single-phase cubic (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 (LBCMT) was reported by Jha et al. [J. Solid State Chem. 177, 2881 (2004)] to exhibit an extraordinarily high effective permittivity (εeff∼6980 and 590 at 1 and 100kHz, respectively) at room temperature. According to x-ray-diffraction analysis, the structure of this perovskite can be fully described on the centrosymmetric space-group Pm3¯m, which precludes the occurrence of ferroelectricity. In the present work, impedance spectroscopy has shown that LBCMT exhibits a bulk permittivity, εr∼40–45, in accordance with that expected for a cubic, centrosymmetric perovskite. LBCMT is a semiconductor with a bulk resistivity of ∼3kΩcm at 300K and an activation energy for conduction of ∼0.20eV which is consistent with an electron hopping conduction mechanism. Finally, it is demonstrated that the high effective permittivity εeff reported previously is not an intrinsic bulk effect arising from hopping conduction between Mn+3 and Mn+4, but is ultimately associated with grain-boundary effects.