Jianrong Zhang

Preparation of copper monosulfide and nickel monosulfide nanoparticles by sonochemical method

This paper presents a novel method for the preparation of copper monosulfide (CuS) and nickel monosulfide (NiS) nanoparticles via a sonochemical route from an aqueous solution containing metal acetate [Cu(CH3COO)2 or Ni(CH3COO)2] and thioacetamide (TAA) in the presence of triethanolamine (TEA) as a complexing agent under ambient air. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray analysis (EDAX). The as-prepared nanoparticles have regular shape, narrow size distribution and high purity. It is found to be a mild, convenient and efficient method for the preparation of CuS and NiS nanoparticles. D 2002 Elsevier Science B.V. All rights reserved.

Magnetic properties of isotropic SrFe12O19 fine particles prepared by mechanical alloying

Abstract M-type Sr-hexaferrites fine particles have been prepared by mechanical alloying. The influences of milling conditions on magnetic properties of SrFe12O19 compounds have been systematically investigated. It can be found that annealing treatment at low temperature can play similar role in structural transformation as compared with long time milling process. For those samples annealed at about 750–800°C, it is clear that saturation magnetization σs values are more sensitive to milling conditions than coercivity values Hc. The maximum σs of 74.8 emu/g and Hc of 5.6 kOe have been obtained in the isotropic powders annealed at 1000°C after milling for 30 h by using high energy mill. With prolonged annealing time, little changes of magnetic saturation and coercivity in powders can be observed and short annealing time results in low properties. The coercive field Hc, as determined from demagnetization curve, corresponds to the pinning or nucleation field.

Preparation and magnetic properties of SrFe12O19 particles prepared by the salt-melt method

Abstract The salt-melt method was adopted to prepare high-performance Sr ferrite without further pulverizing. The reaction path, particles size and magnetic properties have been investigated by using high-purity starting raw materials to synthesize Sr ferrite by replacing SrSO 4 with celestite. The magnetic properties are compared with those of materials prepared by the ceramic process. Due to the lower reaction temperature, no further pulverization is needed and due to low-cost minerals, the process should be more economical than the conventional ceramic process.

Electrical properties of La0.7−xPrxSr0.3MnO3 perovskite

We present the electrical properties of polycrystalline La0.7−xPrxSr0.3MnO3 in which the average ionic radius of the A site 〈rA〉 is systematically varied while keeping the carrier concentration fixed. Below the Curie temperature Tc, the spin-disorder scattering process has been regarded to play an important role in the resistivity. With decreasing 〈rA〉, the structure transition from rhombohedral to orthorhombic phase accompanied with the sharp increase in resistivity at Tc and the increase of the activation energies has been observed.

Preparation of nanocrystalline FeSi alloys and their magnetic properties

Abstract Nanocrystalline FeSi alloys have been prepared using the mechanical alloying method. The structure of the obtained FeSi alloys is the same as that of bcc α-Fe. The final powders obtained mainly consist of particles with a grain size of from a few hundred nanometers to several microns, and the particles are composed of subgrains with a microcrystalline size of about 15–20 nm and an almost completely random orientation with respect to each other. The magnetic properties have also been investigated. The specific saturation magnetization (σs) values are slightly less than those of the corresponding single-crystalline and polycrystalline FeSi alloys, while the coercive force (Hc) values are much higher than those of the corresponding bulk FeSi alloys. The magnetic spectra are all relaxation-type except for Fe75Si25; the values of μ′ and μ″ are comparable to those of ferrite composite materials and domain wall displacements are predominant in the magnetization process.

Sonochemical preparation of lead sulfide nanocrystals in an oil-in-water microemulsion

Lead sulfide (PbS) nanocrystals have been successfully prepared in an oil-in-water microemulsion by a sonochemical method. The product is characterized by using techniques such as X-ray powder diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and energy-dispersive X-ray analysis. The as-prepared PbS nanocrystals crystalize in a cubic structure and have an average crystal size of ca. 11 nm. The product is composed of uniform spherical nanoparticles with narrow size distribution and high purity. A probable mechanism for the formation of nanocrystalline PbS particles in a toluene-in-water microemulsion with the inducement of ultrasound irradiation is proposed. r 2002 Elsevier Science B.V. All rights reserved.

Lattice effect in Pr doped LaSrMnO perovskite

Abstract We have measured resistivity, magnetization and magnetoresistance in polycrystalline La 0.7− x Pr x Sr 0.3 MnO 3 with fixed carrier concentration. With decreasing the average ionic radius of the La site 〈 r A 〉, we found a decrease in T c , an increase in resistivity at T c , and an increase in the magnitude of the magnetoresistance. The samples show a metal-insulator transition in the high-temperature paramagnetic phase with the variation of 〈 r A 〉. These results demonstrate the close relationship between 〈 r A 〉 and the band structure.

Ultrasonic velocity and attenuation in nano-structured Zn materials

By using the gas evaporation method, Zn line particles were prepared, whose average size was about 100 nm. By compacting these Zn particles under different pressures, three nano-structured Zn samples of 2 cm in diameter were produced. Using ultrasonic techniques, ultrasonic velocity and attenuation were measured in the samples in the frequency range from about 2 to 50 MHz.

Strong photoluminescence from Cr3+ doped porous anodic alumina

Samples of Cr 3+ doped porous anodic alumina (PAA:Cr) with different crystal structures were prepared and very strong photoluminescence from a PAA:Cr template calcined at temperature higher than 900 °C was obtained. The crystallization of the PAA:Cr and its influence on the photoluminescence were studied. This kind of PAA:Cr with the template property and strong luminescence may be beneficial in the preparation of composite luminescent nanomaterial.

Magnetic Properties and Magnetic Entropy Changes of Annealed and Melt-spun DyCo2 Alloy

Structure and magnetic properties of annealed and melt-spun DyCo2 alloy were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM) and vibrating sample magneometer (VSM). They both crystallize in the MgCu2-type structure. Curie temperature (TC) of them vary slightly, while their coervicities change remarkably. Annealed DyCo2 alloy has a rather large magnetic entropy change (|ΔSM|) near TC. The magnetization of melt-spun DyCo2 alloy changes gradually in the vicinity of TC. This fact leads to a relatively small |ΔSM| in melt-spun DyCo2 alloy, but the temperature range of |ΔSM| is widen, which is more effective in utility.