Colossal Permittivity and Dielectric Relaxations of (Nb, Al)Co-doped BaTiO$lt;inf$gt;3$lt;/inf$gt; Ceramics

Abstract

Nb and Al co-doped BaTiO 3 ceramics, BaTi 0.98 (Nb 0.5 Al 0.5 ) 0.02 O 3 , have a colossal permittivity ( r 310 5 , tan0.2) at room-temperature. Three distinct relaxation processes are observed in the frequency range from 10 -1 to 10 7 Hz. The low-frequency relaxation between 10 -1 and 10 Hz and the intermediate-frequency relaxation between 10 3 and 10 5 Hz are non-Debye relaxations, which are attributed to Maxwell-Wagner interfacial polarization, electrode interfacial polarization, and barrier layer capacitor. While the high-frequency process between 10 5 and 10 7 Hz is a typical Debye-type relaxation with an activation energy of E15 meV and a frequency factor of f 0 710 6 Hz. The small activation energy and relatively small frequency factor in the BaTi 0.98 (Nb 0.5 Al 0.5 ) 0.02 O 3 ceramics indicate that this relaxation process may derive from local motion of electrons in the complex defect clusters, which results from co-doping and can be named as electron-pinned defect-dipoles. This study suggests that the electron-pinned defect-dipoles mechanism can be used to design colossal permittivity in perovskites, like BaTiO 3 .