Dielectric and ferroelectric characteristics of Ba4Pr2Fe2Nb8O30 tungsten bronze ceramics

Ba4Pr2Fe2Nb8O30 tungsten bronze ceramics have been prepared by a standard solid-state sintering method, and the electrical, dielectric and ferroelectric properties have been determined together with the structure. The structure dependence of ferroelectricity has been investigated by comparing the as-sintered, N2-annealed and O2-annealed samples. The typical relaxor ferroelectric nature is generally indicated in the present ceramics, where the broaden dielectric constant and dielectric loss peaks with strong frequency dispersion feature are observed. The peak temperatures for both dielectric constant and dielectric loss are significantly increased together with the much stronger frequency dispersion by N2-annealing, while the O2-annealing results in the decreased peak temperatures and the suppressed frequency dispersion. These phenomena are closely related to the valences of Fe and Pr ions. The hopping between Fe2+ and Fe3+ inside the grains causes the dielectric relaxation in as-sintered and N2-annealed samples. The enhanced ferroelectricity near room temperature is attributed to the increased ion radius difference between A1 and A2 ions because of the “substitution” Pr4+ for Pr3+ after N2-annealing.