Dielectric and ferroelectric properties of Ba4Gd2Fe2Nb8O30 with filled tungsten-bronze structure

Polycrystalline sample of Ba₄Gd₂Fe₂Nb₈O₃₀ ceramics were prepared by a high temperature solid-state reaction technique. The structure and dielectric properties as well as the behavior of ferroelectric phase transition have been investigated. The dielectric spectra are characterized in wide frequency (40 Hz-1 MHz) and temperature (25degC-600degC). At 1MHz, the room temperature dielectric constant of Ba₄Gd₂Fe₂Nb₈O₃₀ ceramic is 160 together with dielectric loss of 0.054. Two dielectric abnormalities were detected at the temperature dependence of dielectric spectra in low and high temperature ranges, respectively. The low temperature peak (145degC) is frequency independence, while the higher temperature (300degC-600degC) one is extremely high relaxorlike, with very strong frequency dispersion. The high temperature peak was not relaxor ferroelectric but an oxygen defect induced dielectric abnormity, while the low temperature one was proposed to the ferroelectric-paraelectric phase transition. The ferroelectric nature of the present materials is confirmed by the P-E hysteresis loop, with 2Pr of 1.5 muC/cm².