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

Abstract

0.67BiFeO 3 -0.33BaTiO 3 multiferroic ceramics doped with x mol% MnO 2 (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 m to 0.50 m 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 (A 1 -4 mode), 639 cm 1 , and 1338 cm 1 were observed. The blue shifts in the E-4 and A 1 -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 10 3 Hz, and the corresponding dielectric losses were in range of 0.43-0.96, approaching to 0.09 at 10 6 Hz.

Effect of Cobalt substitution on the structural, electrical and magnetic properties of BaTiO<inf>3</inf> ceramics

“…The saturation magnetization (M s ) of the sample increases first and then decreases with the increase of Co doping level, indicating the coexistence of nearest-site antiferromagnetism coupling and next-nearest site ferromagnetic coupling. Similar phenomenon have been observed in Fe doped Ba 0.5 Sr 0.5 TiO 3 [2], Fe doped BaTiO 3 [8], and Fe doped SrTiO 3 ceramics [18]. It is noted that the dopant Co ions start interacting ferromagnetically via the closely placed oxygen vacancies.…”

Improved ferroelectricity and ferromagnetism of Eu-modified BiFeO3–BaTiO3 lead-free multiferroic ceramics

“…The observed Raman modes near 265 and 498 cm -1 can be assigned to the E-4 and A 1 -4 modes of the ceramics, respectively. These modes are in good agreement with those of BiFeO 3 -BaTiO 3 solid solution[29,30]. The Raman peaks near 641 cm -1 should be due to the symmetrical stretching vibrations for the oxygen ions of the FeO6 and MnO 6 octahedral in the BFO-BT-Eu-x ceramics.…”

Enhanced Piezoelectric Properties of Praseodymium‐Modified Lead‐Free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

“…The observed shift of Raman modes toward lower frequencies is associated with the vibrations in sublattice A and is possibly caused by the increase in the mass of the cations of sublattice A. In the harmonic oscillator approximation, the mass and the frequency are connected according to the following dependence 31 :…”

“…The observed shift of Raman modes toward lower frequencies is associated with the vibrations in sublattice A and is possibly caused by the increase in the mass of the cations of sublattice A . In the harmonic oscillator approximation, the mass and the frequency are connected according to the following dependence:where f is frequency of the mode, k is the force constant, and m is the atomic mass of the doped element. Since the atomic mass of Pr is higher than the parent elements ( m Pr = 140.91, m Ba = 137.33, m Ca = 40.08), it is reasonable to expect the negative shift in modes.…”