Structural, spectroscopic, and dielectric characterizations of Mn-doped 0.67BiFeO₃–0.33BaTiO₃ multiferroic ceramics

0.67BiFeO₃–0.33BaTiO₃ multiferroic ceramics doped with x mol% MnO₂ (x = 2–10) were synthesized by solid-state reaction. The formation of a perovskite phase with rhombohedral symmetry was confirmed by X-ray diffraction (XRD). The average grain sizes were reduced from 0.80 μm to 0.50 μm as increasing the Mn-doped levels. Single crystalline nature of the grains was revealed by high-resolution transmission electron microscopy (HRTEM) images and electron diffraction patterns. Polar nano-sized ferroelectric domains with an average size of 9 nm randomly distributed in the ceramic samples were revealed by TEM images. Ferroelectric domain lamellae (71° ferroelectric domains) with an average width of 5 nm were also observed. Vibrational modes were examined by Raman spectra, where only four Raman peaks at 272 cm^-1 (E-4 mode), 496 cm^-1 (A₁-4 mode), 639 cm^-1, and 1338 cm^-1 were observed. The blue shifts in the E-4 and A₁-4 Raman mode frequencies were interpreted by a spring oscillator model. The dieletric constants of the present ceramics as a function of the Mn-doped levels exhibited a V-typed curve. They were in the range of 350–700 measured at 10³ Hz, and the corresponding dielectric losses were in range of 0.43–0.96, approaching to 0.09 at 10⁶ Hz.