Qian Yitai

Preparation of nanocrystalline silver powders by γ-ray radiation combined with hydrothermal treatment

Abstract The γ-radiation combined with hydrothermal treatment method has been successfully used to prepare pure nanocrystalline silver powders from silver nitrate aqueous solutions. Electron microscopy and X-ray powder diffraction techniques show that the average particle size of the prepared silver powder is about 8 nm. Influences of experimental conditions on silver particle size are discussed.

The preparation and structure of a new layered cuprate: TaSr2(NdCe)2Cu2Oy, the Ta analog of the Tl-1222 phase

Abstract A new layered cuprate, TaSr 2 (NdCe) 2 Cu 2 O y has been designed and successfully synthesized. The structure of the compound has been determined by the powder X-ray diffraction method. By indexing of the diffraction patterns, the cell parameters were found to be a = 3.881 A and c = 28.93 A, with a possible space group I 4/mmm . Comparison of the calculated and observed diffraction intensities reveals that the structure is directly related to the TlBa 2 (LnCe) 2 Cu 2 O y (1222 phase) with Ta replacing Tl. Measurement of the resistance from room temperature to 77 K showed that the compound was a narrow-gap semiconductor.

Low temperature synthesis of nanocrystalline Mn3O4 by a solvothermal method

Abstract Nanocrystalline trimanganese tetroxide (Mn 3 O 4 ) has been successfully synthesized by a solvothermal reaction in which KMnO 4 is reduced by CH 3 OH or CH 3 CH 2 OH under pressure. Alcohol also served as the solvent in the method. The reaction temperature can be as low as 80–100°C. Transmission electron micrographs and X-ray powder diffraction patterns show that the average particle sizes are 9–15 nm. From the electron spin resonance (ESR) pattern, hyperfine structure (six absorption peaks of ESR) of Mn 2+ ion is observed on the main line of Mn 3+ . The mechanism for the formation of crystalline Mn 3 O 4 is proposed.

The synthesis and morphological control of nanocrystalline pyrite nickel disulfide and cobalt disulfide

Abstract Nanocrystalline CoS 2 and NiS 2 have been successfully prepared through a solventothermal synthetic route at 130°C. The final products are characterized by X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The sulfur-to-metal ratio of the as-prepared products is ca. 1.99–1 and 1.98–1 for CoS 2 and NiS 2 , respectively. TEM shows that with the change of solvents, the morphologies of the as-prepared sulfides can be controlled.

Solventothermal synthesis and morphological control of nanocrystalline FeS2

One-dimensional nanocrystalline FeS2 has been prepared in ethylenediamine. Much different from other materials, such as CdE (E=S, Se, Te) with hexagonal structure, FeS2 is in cubic structure. The as-prepared FeS2 powders display rodlike morphology with diameters of 20–50 nm and lengths of up to 1000 nm. The morphology control by choosing different solvents is also discussed.

Deposition and microstructural characterization of MgO thin films by a spray pyrolysis method

Abstract Thin films of MgO (150 nm) were deposited by a spray pyrolysis method. Ethanol-water solutions of magnesium acetylacetonate were ultrasonically nebulized and thermally decomposed on to Si(111) and NaCl(100) in the temperature range 400–450°C. The microstructure of as-deposited MgO thin films was studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy.

Hall effect in single phase Ba2YCu3O7−δ

Abstract Results of resistivity, a.c. magnetic susceptibility, Hall effect and superconductivity for single phase Ba 2 YCu 3 O 7− δ are reported. The positive value of Hall constant above T c indicates that the carriers of the sample are hole-like in normal state and its concentration is about 1.1×10 21 cm -3 at room temperature. A large anomaly of R H near T c is observed which may be indicative of granular superconductivity or be related to the intrinsic quality of this class of oxides.

Synthesis and characterization of a new layered superconducting cuprate: RuSr2(Gd,Ce)2Cu2Oz

A new layered superconducting cuprate RuSr2(Gd2−xCex)Cu2Oz with a Tc (onset) of 30 K determined by resistance measurements has been synthesized. The crystal structure is determined by X-ray powder diffraction and Rietveld analysis. The compound RuSr2(Gd2−xCex)Cu2Oz has a tetragonal symmetry with lattice parameters a = 3.8470(5), c = 28.649(1) A for x = 0.6 and a space group of I4/mmm. It is isostructural to the superconductor TaSr2(Ln,Ce)2Cu2Oz.

Growth of Bi2Sr2CaCu2O8 single crystals from Bi-rich melts

Abstract High-quality Bi 2 Sr 2 CaCu 2 O 8 single crystals with dimensions up to 15x4x0.05 mm 3 were grown from the starting composition Bi 2+ x Sr 2 CaCu 2 O y , where x =0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6 and 0.7. Different amounts of Bi 2 O 3 in excess are included in each crystal growth run to act as flux for the growth and the optimum concentrations of the flux amount have been found. Structure characterization of a high-quality 2212 free crystal of 5x1.8x0.02 mm 3 was conducted by the (00 l ), ( h 00) and (0 k 0) X-ray diffractions, using a rotating anode diffractometer, and the back-reflection Laue photograph. It is found that melting incongruency is the main problem encountered in the growth of large and pure-phase single crystals from Bi 2 O 3 -rich melts and we have shown that, for x =0.8, crystals of 2212 phase and crystals of 2201 phase coexisting with CuO are obtained from the two segregated parts of the Bi-rich melts.

Hydrothermal preparation and characterization of nanocrystalline powder of sphalerite

Abstract Hydrothermal treatment has been successfully used to prepare pure nanocrystalline ZnS from amorphous ZnS. XRD indicated that the product was cubic ZnS phase (Sphalerite). Electron microscopy image showed that the average particle size was about 6nm. As-prepared Sphalerite powder with narrow particle size distribution possesses good IR transmittance in the range of 400cm−1 to 5000cm−1.