Effect of rare earth on dielectric properties of Mn contained unfilled tungsten bronze ceramics

Mn contained ceramics with nominal formula Ba4RMn0.5Nb9.5O30 (R = La, Pr, Nd and Eu) were fabricated via a conventional solid−state reaction. The phase structure, microstructure, dielectric and ferroelectric properties of the materials were systematically studied. Ambient temperature XRD patterns indicate that all of the ceramics are single tetragonal tungsten bronze phase with space group P4bm. All of these ceramics present a broad permittivity peak, while only Ba4LaMn0.5Nb9.5O30 exhibits obvious frequency dispersion indicating relaxation. With decreasing A1-site ions size, the maximum dielectric constant temperatures (Tm) gradually increase. The relaxation activation energy and direct current conductivity activation energy of all compounds were obtained by linear fitting with Arrhenius equation. Furthermore, with the increase of the A1-site ions size, the Raman shift moves to a high frequency, indicating that different degrees of lattice distortion. Polarizations versus electric field (P–E) loops measured at ambient temperature show that Ba4EuMn0.5Nb9.5O30 has the highest remnant polarization value.