Sr and Pb co-doping effect on the crystal structure, dielectric and magnetic properties of BiFeO3 multiferroic compounds

Abstract

Bi 1−x (Sr 1/2 Pb 1/2) x FeO 3 (0.10 ≤ x ≤ 0.30) multiferroic compounds have been synthesized by a conventional solid-state reaction. The influences of A-site Sr/Pb co-doping on the structure, dielectric and magnetic properties of BiFeO 3 are investigated systematically. X-ray diffraction reveals that the crystal structure of Bi 1−x (Sr 1/2 Pb 1/2) x FeO 3 transforms from the rhombohedral symmetry (space group R3c) to the cubic symmetry (space group Pm 3 m) with Sr/Pb concentration increasing. Meanwhile, the intensities of Bi-O bond vibrations continuously decrease and finally disappear. The RT polarization versus electric field (P-E) curves conform the ferroelectric nature for all the samples. Furthermore, it is found that the dielectric constant and dielectric loss tangent of the samples measured in the frequency range of 100-10 7 Hz decrease drastically at room temperature. A considerable reduction in the leakage current is observed for BFO with Sr/Pb doping content increasing. The ferromagnetic property enhances with the Sr/Pb substitution increasing, which is ascribed to the cooperation of the Fe 2+-O-Fe 3+ double exchange interaction and the effective suppression of antiferromagnetic cycloidal spin structure caused by the crystalline structure transformation. All results indicate that the Sr and Pb co-doping can effectively improve the magnetic and high-frequency dielectric properties of the multiferroic BiFeO 3 compounds.

Tuning Ferroelectric, Dielectric, and Magnetic Properties of BiFeO3 Ceramics by Ca and Pb Co‐Doping

“…As Ca/Pb content increases from 0.1 to 0.3, the value of 2P r reduces from 0.66 to 0.4 μC cm −2 . In comparison with those of the Sr/Pb co‐doped BFO ceramics, ferroelectric remnant polarization and leakage current of Ca/Pb co‐doped BFO have been further improved significantly, which confirms that Ca doping is more beneficial for the improvement of ferroelectricity and leakage current of BFO ceramics than that of Sr doping. This may be attributed to the possible formation of tetragonal distortion and ferroelectric–paraelectric boundary induced by structural transition from rhombohedral to cubic structure in Ca/Pb co‐doped BFO.…”

“…ϵ r in higher frequency region is mainly dominated by the lone electron pair of Bi 3+ ions. The dielectric constants at 10 MHz for x = 0, 0.1, 0.2, and 0.3 samples are 105, 162, 419, and 508, respectively, obviously higher than those (e.g., 90, 118, 163, and 194 for x = 0.1, 0.18, 0.2, and 0.3, respectively) of Sr and Pb co‐doped BFO ceramics . The small value for the undoped BFO may be the consequence of the parasitic Bi 2 Fe 4 O 9 phase presenting, as revealed by the XRD, degrading the dielectric constant.…”

“…It can be found that the leakage current reduces clearly for BFO with Ca/Pb co‐doping content increasing. Moreover, the minimum leakage current for Sr/Pb co‐doped BFO ceramics was about 10 −5 A cm −2 , whereas that for Ca/Pb co‐doped BFO samples could be lower than 10 −7 A cm −2 , which suggests that Ca/Pb co‐doping has improved leakage current by two orders of magnitude than that of Sr/Pb co‐doping . In general, the leakage current of BFO‐based ceramics can be ascribed to Fe 2+ ions and oxygen vacancies, impurity and pores.…”

“…Stoichiometric amounts of the high purity oxides of Bi 2 O 3 , Fe 2 O 3 , CaCO 3 , and PbO were used as starting materials. The detailed synthesis procedure has been described elsewhere . Typically, the starting oxides were ground for 2 h in an agate mortar and then annealed using alumina crucibles at 825 °C for 30 min in air.…”

“…In our previous report, it was found that Sr 2+ and Pb 4+ co‐doping in BFO ceramics can improve ferroelectric and ferromagnetic properties under charge‐equalization conditions . However, it remains difficult to greatly improve the leakage current and ferroelectricity.…”