Effect of La3+ substitution on the phase transitions, microstructure and electrical properties of Bi1−xLaxFeO3 ceramics

Abstract

Multiferroic Bi1−xLaxFeO3 (x=0.00, 0.05, 0.10, 0.15, 0.20) (represented as B1−xLxFO) ceramics were prepared using the conventional solid state reaction route. The effects of La3+ doping on the density, phase structure, morphology, dielectric and ferroelectric properties were investigated. Judging from X-ray diffraction patterns, all the B1−xLxFO ceramic samples were well crystallized in a pure perovskite phase while the crystal structure changed from rhombohedral to orthorhombic with increasing the La3+ substitution. SEM observations clearly revealed that the grain size was remarkably decreased by La3+ doping. As a result, the ferroelectric Curie temperature was lowered in the La-doped ceramics. However, the abnormal dielectric responses near the antiferromagnetic Néel temperature (TN) demonstrated the existence of remarkable magnetoelectric coupling in the Bi1−xLaxFeO3 ceramics, and the TN was shown to increase substantially with the increase in La3+ doping content. It was found that the dielectric permittivity of the ceramics was significantly increased and the dielectric loss was slightly increased with the increase in La3+ content. The dielectric constant εr of the Bi0.85La0.15FeO3 ceramic at 10kHz reached as high as 1008, 20 times larger than that for pure BiFeO3. In addition, the ferroelectric properties of the B1−xLxFO ceramics were improved and the remanent polarization was increased by La3+ doping. This is probably because the A-site doping with more stable La3+ could reduce the volatilization of Bi3+ and, thus, reduce the concentration of charged defects or defect dipole complexes, such as VO··, VBi‴ or (VBi‴-VO··)′ in the ceramics.