Low dielectric loss induced by annealing in (La_(0.5)Nb_(0.5))_(0.005)Ti_(0.995)O_2 colossal permittivity ceramics

摘要

Low dielectric loss (tanδ＜0.05) within a frequency range of 20 Hz-2 MHz and a temperature range of 25-350 K was obtained through an optimized annealing process in colossal permittivity (CP) (ε'＞ 10~4) (La_(0.5)Nb_(0.5))_(0.005)Ti_(0.995)O_2 ceramics. The effects of annealing on two important dielectric relaxations, electron-pinned defect-dipole (EPDD), and Maxwell-Wagner polarization were explored. An enhancement of activation energy (E_a) value and a large distribution of relaxation time τ were detected in EPDD relaxation for the ceramics annealed at 1123 K. The EPDD polarization was destroyed, accompanied by the disappearance of CP in the high annealing temperature range (＞ 1273 K). Impedance spectroscopy analysis suggested that grain boundary impedance could greatly enhanced as the ceramics were annealed at 1123 K. Strong electrode-material-dependent dielectric properties were detected, and a high tanδ was observed after the insulating surface layer was removed. The CP and low tan5 were ascribed to the maintenance of EPDD polarization, the enhancement of grain boundaries resistance, and the formation of an insulating surface layer through appropriate annealing.