Effect of Gd doping on the structure, dielectric and multiferroic properties of 0.7BiFe<sub>0.95</sub>Ga<sub>0.05</sub>O<sub>3</sub>-0.3BaTiO<sub>3 </sub>ceramics

Abstract

The 0.7Bi<sub>1–<i>x</i></sub>Gd<i><sub>x</sub></i>Fe<sub>0.95</sub>Ga<sub>0.05</sub>O<sub>3</sub>-0.3BaTiO<sub>3</sub> (BG<i><sub>x</sub></i>FG-BT, <i>x</i> = 0, 0.05, 0.1, 0.15, 0.2) ceramics were successfully synthesized via the conventional solid-state reaction method. The effects of Gd doping on crystal structure, microstructure, dielectric, ferroelectric and magnetic properties were systematically investigated. X-ray diffraction analysis indicates that Gd doping induce a structural transition from rhombohedral (<i>R</i>3c) to pseudo-cubic (<i>P</i>4<i>mm</i>) in BG<i><sub>x</sub></i>FG-BT ceramics. Scanning electron microscopy results show a decrease of grain size with doping Gd in BFG-BT. The average grain sizes of the ceramics range from 3.2 μm to 6.2 μm. The dielectric constant and loss tangent are drastically increased and reduced respectively with introducing Gd into the ceramics. Temperature dependent dielectric constant presents a broad peak in the vicinity of Néel temperature (<i>T</i><sub>N</sub>) for all the samples, signifying strong magnetoelectric coupling. An increment in <i>T</i><sub>N</sub> is also observed as a result of Gd-doping in the temperature regions of 230 to 340 ℃. The leakage current density is reduced by about two orders of magnitude under the electric field of 20 kV/cm. This can be ascribed to the reduction of the oxygen vacancy concentration, which is confirmed by the X-ray photoelectron spectroscopy result. The ferroelectricity and ferromagnetism are also improved after the addition of Gd seen from the polarization hysteresis (<i>P</i>-<i>E </i>) loops and the magnetization hysteresis (<i>M</i>-<i>H</i>) loops. The greatly enhanced magnetism with <i>M</i><sub>r </sub>= 0.0186 emu/g and <i>M</i><sub>s</sub> = 1.084 emu/g is obtained in the ceramic with <i>x</i> = 0.2, almost three point six times larger than that of the undoped ceramic.