Papers by Author: Xing Ao Li

Abstract: Pure BiFeO₃ (BFO), Ca-doped and Eu/Ca-codoped BFO nanoparticles were prepared by using a sol–gel method. The effects of Eu/Ca-codoped on the structural, magnetic and ferroelectric properties of the samples were studied. The X-ray diffraction (XRD) analysis reveals a structure transition in the codoped samples. Co-doped samples were obtained with the best ferromagnetic properties, with the largest remaining magnetization Mr = 0.20 emμ/g. The structure transition may be the main cause for the origin of improved magnetic properties, which destroys the space modulated spin structure of BFO and releases the locked magnetic. In addition, the doping of Eu into BFO can reduce the leakage current and enhance the ferroelectric properties.

Abstract: Ni-doped copper nitride films have been prepared by co-sputtering of Ni and Cu targets. The addition of Ni to Cu₃N films reduced the intensity of the (111) diffraction peak, and lead a little angular shifts of the peaks. The films showed a large difference in reflectance in the infrared and visible before and after thermal decomposition, which is applicable to optical recording media. The films change from a semiconductor to a conductor with the increased ratio of Ni in Cu₃N films.

Abstract: Multiferroic BiFeO₃ nanoparticles have been prepared by solgel method. The effects of single-substituted and co-substituted on the structures and magnetism of all the samples are investigated systematically. X-ray diffraction and Raman spectra results confirm that the samples simulate from a distorted rhombohedral structure to a cubic structure. Surface morphology of the samples were examined by scanning electron microscope (SEM). The ferroelectric and magnetic hysteresis loops shows coexistence of magnetism and ferroelectricity in the room temperature. The structure transition may be the main cause for the origin of improved magnetic and ferroelectric properties.

Abstract: Bi0.95Eu0.05Fe0.95Co0.05O3 Nanoparticles sample was prepared by sol-gel process. The microstructure of samples was analysised by X-ray diffraction(XRD), the result indicated that it was the single phase rhombohedral perovskite structure. The morphology of samples was measured by scanning electron microsopy(SEM), the SEM photograph of samples indicated that the nanoparticles of Bi0.95Eu0.05Fe0.95Co0.05O3 sample were small than that of BiFeO3. The valence states of Fe ions in the samples was analysised by the X-ray absorption spectroscopy（XAS）. The XAS of Fe2p showed that it was the mixed valence states (Fe2+ and Fe3+) of Fe ions in samples, and the binding energy of Bi0.95Eu0.05Fe0.95Co0.05O3 was bigger than that of BiFeO3.The magnetic characteristics of the samples were measured by vibrating sample magnetometer (VSM)，the results showed that the weak metamagnetism were obtained from clear hysteresis loop and the magnetic saturation reached 0.408emu/g，compared with BiFeO3 sample, the magnetic properties were significantly enhanced.

Abstract: Copper nitride thin films were deposited on glass substrates by reactive DC magnetron sputtering at various N₂-gas flow rates and different substrate temperature. X-ray diffraction measurements show that the films are composed of Cu₃N crystallites with anti-ReO₃ structure and exhibit preferential orientation to the [111] and [100]. The preferred crystalline orientation of the films changes with the N₂-gas flow rate and substrate temperature. The N₂-gas flow rate and the substrate temperature not only affect the crystal structure of films but also affect the deposition rate, the resistivity and the microhardness of the Cu₃N films.

Abstract: Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were deposited on Pt/Si substrates by RF magnetron sputtering with Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) targets with 50-mm diameter and 5-mm thickness. The microstructure and ferroelectric properties of thin films were investigated. The grain growth behavior and ferroelectric properties such as remanent polarization were different in these two kinds of film, the effects of La doping in the BLT thin film were very obvious.

Abstract: Bi4-xLaxTi3O12 (BLT) ferroelectric thin films were deposited on Pt/Si substrates by RF magnetron sputtering with Bi4-xLaxTi3O12 (x=0.5, 0.75, 1) targets with 50-mm diameter and 5-mm thickness. The effects of La contents on microstructure and ferroelectric properties of Bi4-xLaxTi3O12 thin films were investigated. The grain growth behavior and ferroelectric properties such as remanent polarization were found to be dependent on the La contents in the BLT thin films.