Origin of the high permittivity in (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O-3 ceramics

Single-phase cubic (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O-3 (LBCMT) was reported by Jha [J. Solid State Chem. 177, 2881 (2004)] to exhibit an extraordinarily high effective permittivity (epsilon(eff)similar to 6980 and 590 at 1 and 100 kHz, respectively) at room temperature. According to x-ray-diffraction analysis, the structure of this perovskite can be fully described on the centrosymmetric space-group Pm (3) over barm, which precludes the occurrence of ferroelectricity. In the present work, impedance spectroscopy has shown that LBCMT exhibits a bulk permittivity, epsilon(r)similar to 40-45, in accordance with that expected for a cubic, centrosymmetric perovskite. LBCMT is a semiconductor with a bulk resistivity of similar to 3 k Omega cm at 300 K and an activation energy for conduction of similar to 0.20 eV which is consistent with an electron hopping conduction mechanism. Finally, it is demonstrated that the high effective permittivity epsilon(eff) 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.