Dielectric characteristics of Ba(Fe1∕2Nb1∕2)O3 ceramics were investigated over a broad temperature and a frequency range. Two dielectric relaxations following Arrhenius law were observed at 150–400 and 406–650K. An extremely high relaxorlike dielectric peak (202 270 at 5Hz, 91 930 at 1kHz, and 37 030 at 100kHz) with very strong frequency dispersion was observed at 406–650K, and it was not relaxor ferroelectric but an oxygen defect induced dielectric abnormity. The significant drop of dielectric constant at 146–400K was also frequency dependent, and it was nearly a Debye relaxation. Between these two dielectric relaxations, there was a frequency dependent dielectric constant plateau over a wide temperature interval.

Dielectric relaxations of Ba(Fe1∕2Ta1∕2)O3 ceramics were investigated and discussed over a broad temperature and frequency range. Two dielectric relaxations following Arrhenius law were observed at 153–382 and 440–623K, where there was a giant dielectric constant step between them. The frequency dependent rapid drop of dielectric constant at 153–382K was nearly a Debye relaxation with the intrinsic nature, while the high temperature dielectric relaxation with an extremely high dielectric constant peak and very strong frequency dispersion was attributed to the defect ordering but not a typical relaxor ferroelectric behavior. The O2 annealing almost completely suppressed the dielectric peak and subsequently extended the giant dielectric step, while the low temperature dielectric relaxation and the magnitude of such step were not obviously affected.