Synthesis, Doping And Property Investigation Of BiFeO₃ Powders

Bismutth ferrite(BiFeO3) due to its potential application in spintronic devices, morden optical, new information storage devices and sensors as well as its superior physical properties, raise a wide attention of scientific research workers. BiFeO3 shows a rhombohedrally distorted pervoskite structure and belongs to the R3 c space group, which has lattice parameters, ar=3.965? and αr=89.43° at room temperature. BiFeO3 has very high ferroelectric Curie temperature(TC=830°C) and shows G-type antiferromagnetism Neel temperature(TN=370°C). And it is one of multiferroic materials which simultaneous possess ferroelectricity and antiferromagnetic at room temperature. BiFeO3 with smaller energy band gap(Eg = 2.3 ~ 2.8 eV) also can be used as catalyst for the visible light. However, the researches of optical propertiy are less and lack of a comprehensive understanding. In the paper, we studied the optical properties primarily.In this paper, the pure and Nd(Co)doped BiFeO3 powers were prepared by the hydrothermal synthesis technique at the temperature of 200°C for 24 h using the analytical grade of bismuth nitrate(Bi(NO3)3·5H2O), iron nitrate(Fe(NO3)3·9H2O), neodymium nitrate(Nd(NO3)3·6H2O), cobalt nitrate(Co(NO3)2·6H2O) as iron, bismuth, neodymium and cobalt source, KOH as mineralizer. Morphologies, compositions, structures, optical and magnetic properties of the products were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), energy dispersive X-ray spectrum(EDX), Fourier Transform Infrared Spectroscopy(FTIR), photoluminescence(PL), ultraviolet and visible spectrophotometer(Uv-vis) and physical property measurement System(PPMS). The XRD results show that all the samples were perovskite structure BiFeO3 with a space group of R3 c. We find that the particles are nearly spherical morphology and the size decreases with Nd(Co) doping by SEM. The Uv-vis shows BiFeO3 have a wide absorption band in 500-600 nm wavelength range. The corresponding energy band gap of the samples decreases with the increase of Nd(Co)-doping. The M-H curves also showed that the magnetizations of all samples don’t reach saturation until at a field of 60 KOe and are enhancing with Nd-doping.In addition, Bi1-xCexFeO3(x=0, 0.02, 0.04 and 0.06) nanoparticles were prepared by the sol-gel technique in the thesis. The products were characterized by XRD, SEM, EDX, transmission electron microscopy(TEM), Raman, PL and Uv-vis. The results of XRD show that the Bi FeO3 has the pure phase crystal structure and all the diffraction peaks can well index to a perovskite structure. The result of SEM and EDX indicates that the doped sample contains Bi、Fe、O and Ce elements, and the size decreases with Ce doping. The PL show an intense electronic transition peak at a wavelength of 398 nm, the peak strength enhanced and had slight red shift with the increase of Ce-doping concentration. The Uv-vis shows BiFeO3 have a wide absorption band in 500-600 nm wavelength range. The corresponding energy band gap of the samples decreases with the increase of Ce-doping concentration.