Single-phased ferroelectromagnet BiFeO3 ceramics with high resistivity were synthesized by a rapid liquid phase sintering technique. Saturated ferroelectric hysteresis loops were observed at room temperature in the ceramics sintered at 880 °C for 450 s. The spontaneous polarization, remnant polarization, and the coercive field are 8.9 μC/cm2, 4.0 μC/cm2, and 39 kV/cm, respectively, under an applied field of 100 kV/cm. It is proposed that the formation of Fe2+ and an oxygen deficiency leading to the higher leakage can be greatly suppressed by the very high heating rate, short sintering period, and liquid phase sintering technique. The latter was also found effective in increasing the density of the ceramics. The sintering technique developed in this work is expected to be useful in synthesizing other ceramics from multivalent or volatile starting materials.

Room-temperature saturated ferroelectric polarization in BiFeO3 ceramics synthesized by rapid liquid phase sintering

Wang et al recently reported multiferroic behavior, with ferromagnetic and ferroelectric polarizations that are both large at room temperature, in thin strained films of BiFeO3 (BFO). Although at room temperature, bulk BFO is ferroelectric and anti-ferromagnetic , Wang et al. reported that a 70-nm film shows both an enhanced ferroelectric polarization (90 μC cm–2) and a substantial magnetization (1 μB/Fe). This remains the only report of a robust room-temperature multiferroic and suggests the potential for novel devices that exploit the anticipated strain-mediated magnetoelectric coupling between the two ordered ground states. In this Comment, we argue that epitaxial strain does not enhance the magnetization and polarization in BiFeO3

https://science.sciencemag.org/content/sci/307/5713/1203.1.full.pdf

Comment on "Epitaxial BiFeO3 multiferroic thin film heterostructures".

Multiferroic bismuth ferrite-based materials for multifunctional applications: Ceramic bulks, thin films and nanostructures

Bismuth ferrite (BiFeO3) uniform microcrystals with various morphologies (microspheres and micro/submirocubes) were successfully synthesized by a controlled hydrothermal method. The resulting microstructures were characterized using X-ray diffraction, scanning/transmission electron microscopies and Raman spectroscopy. Possible formation mechanism for BiFeO3 microcrystals was proposed. UV−vis spectra showed that the optical properties of the microsized BiFeO3 crystals were strongly related to their shape and size. We further demonstrated the useful photocatalytic activity of these regular-shaped structures as determined by degradation of Congo red under visible-light irradiation (λ > 400 nm). Additionally, magnetic responses were observed to be influenced by the morphology of as-synthesized BiFeO3 products, and the ferroelectric performance of BiFeO3 submicrocube was also studied by piezoelectric force microscopy (PFM). Being a multiferroic semiconductor with suitable narrow band gap (∼2.2 eV) and uniform ...

Controlled Fabrication of BiFeO3 Uniform Microcrystals and Their Magnetic and Photocatalytic Behaviors

Ba doped BiFeO3 compounds were prepared by a solid-state reaction. X-ray diffraction showed that Bi1−xBaxFeO3 was single phase up to x=0.25. These samples exhibited magnetism and ferroelectricity simultaneously at room temperature. The magnetoelectric coupling was evidenced by the increase of the dielectric constant with the increase of the applied magnetic field. For Bi0.75Ba0.25FeO3 with ΔH=8kOe, the values of [er(H)−er(0)]∕er(0) are 1.7% and 1% for 80 and 300K, respectively.

Effect of Ba doping on magnetic, ferroelectric, and magnetoelectric properties in mutiferroic BiFeO3 at room temperature

The difficulties in synthesizing phase pure BiFeO3 are well known. In this letter we are reporting the optimized synthesis conditions for obtaining phase pure BiFeO3 ceramic. The oxide mixing technique followed by leaching with dilute nitric acid has been used for the synthesis. X-ray diffraction pattern indicated that the sample is phase pure. Scanning electron microscopy along with energy dispersive x-ray fluorescence analysis confirmed the chemical homogeneity of the sample. No segregation of the impurity phase in the matrix was detected. Moreover, Bi/Fe atomic ratio is observed to be ∼1. The ferroelectric transition of the sample at 836 °C has been detected by differential thermal analysis.

V. R. Palkar

Papers

Ferroelectricity in a pure BiFeO3 ceramic