Haixing Zheng

Control and effects of Cu(I) and Cu(II) ions in BiCaSrCuO glasses

The influence of glass preparation on the Cu(I)/Cutotal ratio in BiCaSrCuO glasses has been investigated. It was found that copper ions in the glasses exist mainly in the Cu(I) ionic state. Additionally, the Cu(I)/Cutotal ratio increases with the glass melting temperature and changes slightly with copper oxide content. The number of glass network units, [BiO3] pyramids, decreases in the BiCaSrCuO glasses when the Cu(I)/Cutotal ratio and copper oxide content increase. As a consequence of these changes the glass transition temperature, Tg, and the glass crystallization temperature, Tx, decrease and the glass becomes thermally unstable: the value of (Tx − Tg) of the glass decreases. The initial crystalline phase from these glasses in the Bi2Sr2CuOy phase. The glasses with the lower Cu(I)/Cutotal ratio from larger crystalline.

Some optical properties of infrared transmitting Bi‐Ca‐Sr‐Cu‐O glasses

Glasses based on Bi2O3, CaO, SrO, and CuO were first prepared as precursors to polycrystalline superconducting ceramics based on these oxides. These glasses were found to be transparent in the infrared to 11 μm. The infrared cutoff is approximately 6.5 μm. The refractive indices are surprisingly high being about 2.9.

The Control of Precipitation in Sol-Gel Solutions

The preparation of homogeneous gels from liquid solutions necessitates the prevention of precipitation. This becomes increasingly difficult in multicomponent systems. Currently, there are no systematic considerations on precipitation in sol-gel solutions. This paper is concerned with the methods to control precipitation in alkoxide solutions. Each method is applied to specific systems, containing alkoxides of various metals, such as yttrium, lanthanum, barium, and titanium, in alcoholic solutions.

Chemically Designed, UV Curable Polycarbosilane Polymers

To prepare new polycarbosilane polymer precursors with high solubility and the capability of UV cross-linking, commercial polycarbosilane was modified by a chemical route. These modifications involved AlCl 3 catalyzed chlorination reactions of polycarbosilanes Si-H bonds. The resultant Si-Cl bonds were substituted by a reaction with sodium acetylyde to form Si-C=CH ligands. These ligands are suitable for controlled, free radical initiated cross-linking of the polycarbosilane polymers. The increase in molecular weight should allow for increased Tgs and the retention of polymer pre-forms. In this report, the chlorination of the polycarbosilane polymer and the substitution reactions of polycarbosilane were examined with IR, 29 Si and 13 C NMR spectroscopy. In addition, the retention of polymer pre-forms were analyzed after UV exposure and inert atmosphere pyrolysis.

Boron Carbide-Based Ceramics Via Polymer Route Synthesis

Boron carbide is a ceramic material with excellent high temperature physical properties. As compared to conventional techniques, the preparation of boron carbide from polymeric precursors is attractive as this technique offers a number of unique advantages. In this paper, the screening of polymeric precursors to boron carbide will be discussed. Two promising boron carbide, carborane containing polymeric precursors have resulted in 60-70 wt.% ceramic yields. The chemistry of polymer synthesis and the transformations from the polymer to amorphous and crystalline boron carbide were investigated with infrared spectroscopy, NMR spectroscopy, thermal analysis, and x ray diffraction.

Properties of the infrared transmitting Bi-Ca-Sr-(Cu, Zn)-O glasses doped with lead oxide

The glass forming regions of the Bi015-CuO-Ca05Sr05O superconducting system have been explored by the addition of PbO. The glass froming regions expand with PbO addition and shrink with the substitution of copper oxide by zinc oxide. The glass transition temperature of these glasses ranges from 300C to 420C. These glasses have high refractive index of about 2. 8 and density from 6 to 9 g/cm3 they are infrared transmitting with cutoff wavelength farther than 7 tm. The high polarizability of Bi3 ions gives these glasses high non-linear optical coefficient of 4 * lO13. 1.

Alkynyl Substituted Carboranes as Precursors to Boron Carbide Thin Films, Fibers and Composites

The use of alkynyl substituted derivatives of o-carborane as precursors to boron containing ceramics is described. These compounds undergo a thermally or photochemically induced polymerization to afford cross linked polyakynyl-o-carborane derivatives. The increase in molecular weight should allow for increased Tgs and the retention of modelled polymer preforms. In this report, these modification reactions are described. In addition, the retention of molded polymer preforms were analyzed after UV exposure and inert atmosphere pyrolysis.

Potential Application of Bi(Pb)-Ca-Sr-Cu-O Glasses for Preparation of Integrated Optical Fibers

The infrared transmission, and possible high nonlinear optical susceptibility of Bi(Pb)-Ca- Sr-Cu-O glasses as well as their being the precursors for high temperature superconductors make them potential materials for integrated optical fibers. In this work, the glass formation and the fabrication of glass fibers have been investigated. The properties of the glasses have been studied. The infrared cutoff of the glasses is above 7 μm, and a high refractive index (˜ 2.9) and a high density (˜ 6 g/cm 3 ) indicate the possible high nonlinear optical susceptibility. After being heat treated at high temperatures, the glasses become superconductors which show the response to the optical radiation due to the bolometric effect. Fabrication of an integrated optical fiber system incorporating the transmitting medium, optical modulator and detectors is possible.

Control of YBA2CU3OY Sol-Gel Solution Structure by Chemical Modification of Organic Acid and its Effects,

Abstract : Since the discovery of the high temperature superconducting ceramics, numerous techniques have been tested in order to overcome the difficulties in the fabrication (e.g. porosity, preparation of specific shapes). The sol-gel process has been demonstrated to be ideal for the fabrication of high Tc superconducting ceramic fibers or wires (1). In the sol-gel process, the metal alkoxides in organic solvents are hydrolysized and polymerized (2). These low temperature solution reactions yield the ultrahomogeneity of materials and low final phase-forming and densification temperature (3). By controlling the hydrolysis and polycondensation reactions a homogeneous solution with proper viscosity can be made for the fiber drawing and film coating (4). Water content, modification of sol-gel solution are two common techniques to control a solution reaction 1,5. Here we have studied the structure change induced by the modification of the metal alkoxide solution by 2EHA. Further effects of 2EHA on the formation of YBa2CU307-x, microstructure and superconductivity of final products have been investigated.