Lizhu Song

A study on the coercivity and the magnetic anisotropy of the lithium ferrite nanocrystallite

Lithium ferrite nanocrystallites ranging from several nanometres to several hundreds of nanometres in size have been prepared by the polyethylene glycol gel method. These nanocrystallites were identified as pure lithium ferrite by x-ray diffraction analysis. Their magnetization and de-magnetization were measured by using a vibrating sample magnetometer at different temperatures. The specific saturation magnetization and the coercivities change with the diameter of these nanocrystallites and with temperature. The effective magnetic anisotropy constants of these samples were deduced by using the law of approach to saturation. It is found that the value of a lithium ferrite nanocrystallite of diameter 9.1 nm is about ten times greater than the magnetocrystalline anisotropy constant of bulk lithium ferrite. The coercivities of these nanocrystallites at different temperatures were calculated by using the mixed coercivity model. The calculated coercivity results are consistent with the experimental ones.

Photoluminescent properties of ZnS:Mn nanocrystals prepared in inhomogeneous system

Abstract ZnS:Mn nanocrystalline colloids and powders were prepared by chemical method with H 2 S gas in an inhomogeneous system of gas–liquid phase. The best reactive conditions were determined. The structure and the properties of the materials were examined by X-ray diffraction (XRD) and infrared (IR) spectroscopy. From the PLE and PL spectra of ZnS:Mn nanocrystals, it is shown that the Mn 2+ ions are incorporated into the ZnS host structure. The position of the characteristic peaks in the PLE spectra of ZnS:Mn nanocrystal sol or powders shift to higher energy under UV exposure, and are different from those of ZnS:Mn bulk materials. The emission sites of ZnS:Mn nanocrystal sol and powders are different from the bulk materials, but the emission sites of nanocrystal powders are the same as those of nanocrystal sol.

Study of optical properties of manganese doped ZnS nanocrystals

ZnS:Mn nanocrystals were prepared by the coprecipitation method. The reaction conditions, such as the amount of manganese doped, the concentration of the reactant, the surfactant, the reactive temperature and time were studied systematically. Nanocrystalline powders and sols exist. The photoluminescent excitation spectra and the photoluminescence spectra of ZnS:Mn nanocrystal were studied by the fluorescent divide spectroscopy under an ultraviolet excitation. It is shown that the luminescent sites of the nanocrystalline powder and sol are different from that of ZnS:Mn bulk crystal. The luminescent site of the sample results from the transition of the doped Mn2+ in the ZnS crystal.

Preparation, characterization and catalytic activity of sulfated zirconia–silica nanocrystalline catalysts

Abstract Sulfated zirconia–silica (SO42−/ZrO2–SiO2) precursors were prepared by chemical methods in three steps. The precursors were calcinated at different temperatures to form the SO42−/ZrO2–SiO2 nanocrystalline catalysts. The reaction conditions were optimized, such as ZrO2 content, volume ratio of water–ethanol, amount of HNO3 and reactive temperature and time. The specific surface area, heat stability and structure properties of catalysts were examined by X-ray diffraction (XRD), IR and differential thermal analysis (DTA). The specific surface areas of ZrO2–SiO2 and SO42−/ZrO2–SiO2 are 800 and 400 m2/g, respectively. They are higher than that of ZrO2 and SO42−/ZrO2. It was shown that there are very strong interactions between SO42− and ZrO2–SiO2. The acidic properties of SO42−/ZrO2–SiO2 were tested by Hammett indicator method. Through the acetic acid (HAc) reaction with glycerin, it was shown that the SO42−/ZrO2–SiO2 catalyst has highly active sites and high catalytic activity.

The effect of pressure on the specific surface area and density of nanocrystalline ceramic powders

Abstract Nanocrystalline LaFeO3, LaCoO3, La1-xSrxFeO3 and La1-xSrxFe1-yCoyO3 powders were compacted at room temperature, under pressures of 0.0, 0.5, 1.0 and 1.5 GPa, respectively. The specimens were examined by rotating anode X-ray diffractometry and their specific surface areas and densities measured. Results show that deformation, fracture and phase transition can occur to different extents in the nanocrystalline materials subjected to different compaction pressures. The characteristics of the interfaces, which are changed under the contact stresses between adjacent crystalline grains, are related to the compaction pressure and the types of interaction forces between interfacial atoms, which may be between those of van der Waals bonds and covalent bonds. The specific surface area and the density of the nanocrystalline materials change with increasing compaction pressure.

Magnetic properties of nanocrystalline LiFe5O8 particles

Abstract Nanocrystalline LiFe 5 O 8 particles of several nanometers in size have been prepared by the PEG gel method, their particle structure, morphology and magnetic properties were examined by XRD, TEM and VSM. It was found that σ s /σ bulk decreases with decreasing particle size, where σ s is the saturation magnetization. The surface effect is probably the dominant effect in the decrease of σ s . The Curie temperature of LiFe 5 O 8 (9.1 nm in diameter) decreased to 580°C which is lower than that of bulk LiFe 5 O 8 (620°C).

Phase diagrams of ternary alloy systems at high pressure

Abstract High pressure phase diagrams of ternary alloy systems have been studied both theoretically and experimentally. A straightforward method of obtaining complete and accurate high pressure multicomponent phase diagrams is proposed by combining theoretical calculation with experimental determination.

Determination of the phase diagrams of the Cd-Sn(0.2)-Zn ternary system at high pressure

Abstract In order to verify the calculated result of the high-pressure phase diagram of the ternary alloy system, several vertical sections of the phase diagram of Cd-Sn-Zn system with a constant mole fraction XSn = 0.2 were determined by differential thermal analysis at high pressures. The working pressures were 0, 0.5, 1.0, 1.5, 2.0 GPa. The liquidus determined at ordinary pressure tallies well with that reported by Bray. The eutectic temperature of the system increases by about 50 K on going from atmospheric pressure to high pressure 2.0 GPa. The composition of the phase boundary L/L + S1 + S2 changes by about 0.1 mole fraction to the zinc-rich side.

Determination and calculation of the CdPbSn ternary phase diagram

Abstract Six vertical sections of the CdPbSn ternary phase diagram (Cd60wt.%Pb40wt.%Sn, Pb20wt.%Cd80wt.%Sn, Sn70wt.%Cd30wt.%Pb, Cd30wt.%Pb, Cd30wt.%Pb70wt.%Sn, Cd80wt.%Pb20wt.%Sn and Cd90wt.%Pb10wt.%Sn) were determined and calculated. The calculations agreed well with the experimental results. A complete liquidus projection of the CdPbSn system was also derived from the calculations.