Benfang Yu

Effects of ion doping at different sites on electrical properties of multiferroic BiFeO3 ceramics

Pure, La3+ doped at A site, V5+ doped at B site, and La3+ and V5+ co-doped multiferroic BiFeO3 ceramics: BiFeO3 (BFO), Bi0.85La0.15FeO3 (BLF), BiFe0.97V0.03O3 (BFV), Bi0.85La0.15Fe0.97V0.03O3 (BLFV), etc were successfully prepared by a rapid liquid sintering technique. X-ray diffraction indicated that these ceramics were of polycrystalline perovskite structures, accompanied with a tiny residual Bi2O3 phase. It was found that, among these ceramics, BLFV ceramic exhibited the best electrical properties. The leakage current density of BLFV ceramic was only 2.1 × 10−6 A cm−2 at 10 kV cm−1, two and one orders of magnitude lower than those of the BLF and BFV ceramics, respectively. In the measuring frequency of 4 KHz–1 MHz, the dielectric constants and losses of this sample exhibited slight variation and the lowest loss tangent was 0.08. The sample had a relatively saturated ferroelectric hysteresis loop. These suggested that the co-doped BiFeO3 ceramic by La3+ and V5+ at A and B sites showed advantages in application over the pure BFO, doped BLF and BFV ceramics, respectively.

Enhanced electrical properties in multiferroic BiFeO3 ceramics co-doped by La3+ and V5+

La3+ and V5+ co-doped Bi0.85La0.15Fe1?xVxO3 (BLFVx, x = 0?0.1) ceramics were prepared by a rapid liquid sintering technique. The effects of the V5+-doping content on the structure and electrical properties of BLFVx ceramics were investigated. In the range of the V5+ content x from 0 to 0.03, BLFVx ceramics had a polycrystalline perovskite structure with tiny residual Bi2O3, while an impurity phase appeared for x > 0.03. As the x increased from 0 to 0.1, both the leakage current density and the dielectric loss (tan ?) for BLFVx ceramics decreased gradually, while the dielectric constant (?r) first increased and then decreased gradually in this process, reaching a maximum value of 273 for x = 0.03. Among the BLFVx ceramics, the BLFVx=0.01 ceramic showed a well-saturated hysteresis loop with large remanent polarization (Pr) of 39.4??C?cm?2 and a low coercive electric field (Ec) of ?43.1?kV?cm?1 under an applied electric field of ?75?kV?cm?1. In addition, these ceramics exhibited good anti-fatigue characteristics after 2 ? 1010 read/write polarization cycles. These suggested that La3+ and V5+ co-doping was beneficial for enhancing the dielectric, ferroelectric and anti-fatigue properties of the BLFVx ceramics.

Enhanced multiferroic properties of BiFeO3 thin films by Nd and high-valence Mo co-doping

Pure BiFeO3 (BFO), Nd-doped BFO (BNF) and Nd and Mo co-doped BFO (BNFM) multiferroic thin films were prepared by pulsed laser deposition on Pt/Ti/SiO2/Si substrates. Among these films, the BNFM film exhibited the lowest dielectric loss and leakage current density, a well-saturated P–E loop, excellent charge-retaining ability and fatigue-free behaviour. Furthermore, improved ferromagnetism was observed in this film with a saturation magnetization of ~15 emu cm−3. These significant improvements in ferroelectric and ferromagnetic properties could be preliminarily attributed to the elimination of oxygen vacancies and the increase in the Fe2+ ions in the film by Nd and high-valence Mo co-doping, respectively.

Effect of Ce doping on the microstructure and electrical properties of BiFeO3 thin films prepared by chemical solution deposition

Ce-doped Bi1−xCexFeO3 (BCFOx) thin films with x = 0–0.12 were successfully prepared on SnO2 : F(FTO)/glass substrates by chemical solution deposition. The BCFOx films showed a gradual phase transition from a rhombohedral to a pseudotetragonal structure with increase in the Ce content. The substitution of Bi with Ce greatly reduced the leakage current and the dielectric loss of the BCFOx films, which showed an Ohmic conduction mechanism. The BCFOx films with x = 0.06 exhibited a well squared-shaped P–E hysteresis loop with a remanent polarization (2Pr) of 92.3 µC cm−2 and an improved anti-fatigue characteristic after 1010 read/write polarization cycles.

Structural Transition and Multiferroic Properties of Eu-Doped BiFeO3 Thin Films: Structural Transition and Multiferroic Properties of Eu-Doped BiFeO3

The Bi1−xEuxFeO3 (x=0, 0.05, 0.10, 0.15, 0.20, and 0.30) thin films were grown by pulsed laser deposition on Pt/Ti/SiO2/Si substrates, and the effects of Eu content on the structure and multiferroic properties were investigated. A structural transition from rhombohedral R3c to orthorhombic Pbnm occurred in the film with x=0.15 due to the increase of the Eu content. Superior multiferroic properties were obtained in the film with x=0.10, giving a remanent polarization Pr=74 μC/cm2 and a coercive field Ec=250 kV/cm at an applied electric field E=560 kV/cm, a good antifatigue property, and a saturated magnetization Ms=3.5 emu/cm3. These significantly improved ferroelectric properties could be attributed to the appropriate lattice distortion and the lower leakage current due to the doping, while the enhanced ferromagnetism might be ascribed to the substitution-induced suppression of the spiral spin modulation.

Greatly reduced leakage current in BiFeO3 thin film by oxygen ion implantation

Oxygen ions are implanted into BiFeO3 films on LaNiO3/SrTiO3(1 0 0) substrates. The evolution of films is characterized by x-ray diffraction, scanning electron microscopy and cross-sectional transmission electron microscopy. The leakage current density of the implanted films is lowered by two orders of magnitude in comparison with unimplanted BFO films. The mechanisms for reduced leakage current in BiFeO3 thin films are discussed.

Multiferroic Properties of Rare-Earth Eu and Nd Doped BiFeO3 Thin Films

Pure BiFeO3 (BFO), Eu doped BFO (BEF), and Nd doped BFO (BNF) multiferroic films were prepared by pulsed laser deposition on Pt/Ti/SiO2/Si substrates. XRD analysis revealed that the films had the rhombohedral structure with doping-induced lattice distortion. The Eu and Nd doping significantly improved the dielectric, ferroelectric, and ferromagnetic properties of the BFO films. Saturated hysteresis loops were observed in BEF and BNF films with remnant polarization of 37 μC/cm2 and 60 μC/cm2, respectively. The magnetization was demonstrated with remnant magnetization of 0.10 emu/cm3 and 0.60 emu/cm3 for the BEF and BNF films, respectively. The improvements and mechanism of different element doping on the properties of the BFO films were discussed.