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.
This work is financially supported by the National Natural Science Foundation of China (Grant Nos. 10874065, 11174122 and 11134004), the National Basic Research Program of China (Grant Nos. 2009CB929503 and 2012CB619400), key project from Ministry of Science and Technology of the People's Republic of China (Grant No. 2009ZX02101-4), and Analysis & Test Fund of Nanjing University. T. Al-Kassab acknowledges the generous support of the KAUST baseline funds.
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