Origin of the high permittivity in (La0.4Ba0.4Ca0.2)(Mn0.4Ti0.6)O3 ceramics
Abstract
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 (ɛeff~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 Pm3m, which precludes the occurrence of ferroelectricity. In the present work, impedance spectroscopy has shown that LBCMT exhibits a bulk permittivity, Vr~40-45, in accordance with that expected for a cubic, centrosymmetric perovskite. LBCMT is a semiconductor with a bulk resistivity of ~3 kΩ cm at 300 K and an activation energy for conduction of ~0.20 eV which is consistent with an electron hopping conduction mechanism. Finally, it is demonstrated that the high effective permittivity Veff 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.
- Publication:
-
Journal of Applied Physics
- Pub Date:
- October 2005
- DOI:
- 10.1063/1.2089159
- Bibcode:
- 2005JAP....98h4101L
- Keywords:
-
- 77.84.Dy;
- 77.22.Ch;
- 77.80.-e;
- 72.80.Sk;
- 61.72.Mm;
- 72.20.Ee;
- Niobates titanates tantalates PZT ceramics etc.;
- Permittivity;
- Ferroelectricity and antiferroelectricity;
- Insulators;
- Grain and twin boundaries;
- Mobility edges;
- hopping transport