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Gao X.,Kunming University of Science and Technology | Gao X.,Key Laboratory of Advance Materials of Yunnan Province | Gao X.,Key Laboratory of Advance Materials of Precious Nonferrous Metals | Gan G.,Kunming University of Science and Technology | And 15 more authors.
Key Engineering Materials | Year: 2012

To better understand the effects of Co-doping with Cr, Mn, and Co on electronic structure and the density of states of ZnO, the theoretical study was carried out by means of first principles and pseudopotentials method based on density functional theory (DFT). Portion of Zn atoms in ZnO were crystal randomly substituted by Mn, Cr or Co elements, and the electronic structure of Cr 2+, Mn 2+ and Co 2+ changed into 3d 4, 3d 5 and 3d 7, resulting in enhanced localized magnetic moments in ZnO. It was concluded that electronic properties of ZnO were not only related to electron energy level, but also associated with electron spin, with spin-dependent scattering and spin-dependent hopping conductivity as maybe two important mechanisms. © (2012) Trans Tech Publications.


Kang K.,Kunming University of Science and Technology | Kang K.,Key Laboratory of Advance Materials of Yunnan Province | Kang K.,Key Laboratory of Advance Materials of Precious Nonferrous Metals | Gan G.,Kunming University of Science and Technology | And 20 more authors.
Journal of Semiconductors | Year: 2015

An investigation was made into the effect of doping with the elemental crystal Ge or/and GeO2 on the TiO2-V2O5-Y2O3 varistor ceramics. The result shows that as the doping contents of V2O5 and Y2O3 are 0.5 mol%, respectively, co-doping with 0.3 mol% Ge and 0.9 mol% GeO2 makes the highest α value (α = 12.8), the lowest breakdown voltage V1mA (V1mA = 15.8 V/mm) and the highest grain boundary barrier ΦBB = 1.48 eV), which is remarkably superior to the TiO2-V2O5-Y2O3 varistor ceramics undoped with Ge and GeO2 and mono-doped with Ge or GeO2. The TiO2-V2O5-Y2O3-Ge-GeO2 ceramic has the prospect of becoming a novel varistor ceramic with excellent electrical properties. © 2015 Chinese Institute of Electronics.


Liang Z.,Kunming University of Science and Technology | Liang Z.,Key Laboratory of Advance Materials of Yunnan Province | Liang Z.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.Y.,Kunming University of Science and Technology | And 17 more authors.
Advanced Materials Research | Year: 2014

Based on the density functional theory, the geometrical structure optimization and electronic structure of ZnO (1120) surfaces were calculated. ZnO (1120) surfaces in the structural relaxation, electron density difference, densities of states and the Ti adsorption were analyzed by using the first-principles and pseudopotential method. According to the computing result, the geometrical structures of the unabsorbed ZnO (1120) surfaces and the Ti-adsorbed ZnO (1120) surfaces are similar. When Ti adsorbs ZnO (1120) surfaces, the negative charge density is special high in the central region between Ti and O. Ti-O shows obviously better performance than Zn-O in covalent bond. The Ti-adsorbed ZnO (1120) surfaces have metallic characteristics because of the number of outer electron transferred from Ti to O is extremely limited and the area of negative charge of the surface is large. © (2014) Trans Tech Publications, Switzerland.


Fan M.Y.,Kunming University of Science and Technology | Fan M.Y.,Key Laboratory of Advance Materials of Yunnan Province | Fan M.Y.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.Y.,Kunming University of Science and Technology | And 20 more authors.
Advanced Materials Research | Year: 2014

The content and particle size of the Na - Ca System glass powder have significant effects on the properties of the silver paste. The effects of the sintering temperature, holding time, glass powder content and glass powder size on the adhesion and square resistance of the silver film were studied. The conductive network of the silver film was observed by SEM. The research results show that the silver paste with 6 wt.% content of the 2.47μm glass powder sintered at 680°C for 7 minutes have good properties. The adhesion strength and square resistance of the silver film are respectively 2.5 N/mm2 and 14 mΩ /. © (2014) Trans Tech Publications, Switzerland.


Zhu H.,Kunming University of Science and Technology | Zhu H.,Key Laboratory of Advance Materials of Yunnan Province | Zhu H.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.,Kunming University of Science and Technology | And 17 more authors.
Advanced Materials Research | Year: 2012

SnO-B 2O 3-SiO 2 glass powders, in which the different contents of SnO and B 2O 3 were 35% ∼ 70%wt and 26% ∼ 61% wt respectively, were prepared through high-temperature melting, water quenching and Ball milling. XRD showed that the performance of forming glass was very good and the range of extension was very wide. The effect of the contents of SnO and B 2O 3 on Tg, acidoresistant and density of prepared glass was studied. IR showed that it generates the heavy metal oxide generated glass. The density of glass powder decrease with increase of B 2O 3 content, but increase with increasing SnO content. SnO-B 2O 3-SiO 2 glass had excellent chemical stability. Differential thermal analysis (DTA) shown that, with increasing SnO content, glass transition temperature first lower and then decreased.


Zhang L.,Kunming University of Science and Technology | Zhang L.,Key Laboratory of Advance Materials of Yunnan Province | Zhang L.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Du J.,Kunming University of Science and Technology | And 11 more authors.
Advanced Materials Research | Year: 2012

Porous alumina insulation materials were prepared by the combination method of gelcasting and foaming. The effects of the amount of blowing agent, the solid volume, and the sintering temperature on porosity of aluminum oxide ceramic were studied. The result showed that, when the amount of blowing agent is 1wt %, the solid volume is 45 vol % and the sintering temperature is 1500°C, the porous alumina ceramics with high porosity, small pore diameters, evenly distributed, high bending strength and low heat conductance can prepared.


Yang C.-J.,Kunming University of Science and Technology | Yang C.-J.,Key Laboratory of Advance Materials in Rare and Precious and Nonferrous Metals | Yang C.-J.,Key Laboratory of Advance Materials of Yunnan Province | Du J.-H.,Kunming University of Science and Technology | And 11 more authors.
Cailiao Kexue yu Gongyi/Material Science and Technology | Year: 2012

To precisely control the reaction conditions of doped TiO2 powders prepared by coprecipitation-coating process, the ions precipitation reaction equilibrium of Men+(Ni2+/La3+/ Fe3+/Al3+) in NaHCO3-NH3·H2O system was discussed by thermodynamic analysis in this paper. The relation curves between total concentrations of each metal ion and pH value under different total ammonia concentrations cN and total carbon concentrations cC were obtained. Then, the suitable pH of complete precipitation for all metal ions was determined. The results show that when cN is 0.010 mol/L, and cC is 1.000 mol/L, the optimal pH is 9.0 to prepare the doped titanium dioxide powders by coprecipitation-coating process, and the precipitants are NaHCO3 and NH3·H2O.


Yan J.,Kunming University of Science and Technology | Yan J.,Key Laboratory of Advance Materials in Rare and Precious and Nonferrous Metals | Yan J.,Key Laboratory of Advance Materials of Yunnan Province | Gan G.,Kunming University of Science and Technology | And 8 more authors.
Yadian Yu Shengguang/Piezoelectrics and Acoustooptics | Year: 2011

Formation mechanism of secondary phase in (La, Nb) co-doped TiO 2 ceramics varistor were investigated. The (La, Nb) co-doped TiO 2 ceramics samples were prepared from anatase TiO 2, Nb 2O5 and La 2O 3 oxide powders by a traditional solid-state sintering method. Microstructure, chemistry composition, crystal structure, thermal etched groove and micrograph of in (La, Nb) co-doped TiO 2 ceramics were tested by SEM, EDS, XRD, AFM and TEM. Formation mechanism of secondary phase was discussed by point defect thermo-dynamical analysis, grain boundary energy and materials structure measurement. The results showed that secondary phase were originated from doping ion La 3+ and Nb 5+ segregation at grain boundaries of in (La, Nab) co-doped TiO 2 ceramics. The driving force of segregation was the elastic strain energy. The segregated ion nucleated at grain surface or grain boundaries interface with higher energy. The nucleation gradually grew to form secondary phase at during high-temperature sintering. The growth of secondary phase was mainly on crystal planes with higher energy to minimize the materials system energy.


Zhang Z.,Kunming University | Zhang Z.,Key Laboratory of Advance Materials of Yunnan Province | Zhang Z.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.,Kunming University | And 15 more authors.
Key Engineering Materials | Year: 2012

To understand the atomic structure and electronic properties of Cr atom adsorbed on polar ZnO surfaces, a theoretical study is carried out by means of first-principles calculations based on density functional theory. The results show different characteristic with the different adsorption sites for Cr. The Cr atom adsorbed at the site on top of O forms a strong ionic bond with O atom, with electrons transferred to O. While for the Cr atom adsorbed at the hcp-hollow site on Zn-terminated surface, it forms a metallic bond with the surface Zn atom, which exhibits a free-electron-like behavior. The adsorbed atoms could not effect more atoms in ZnO due to a strong screening of ZnO to the outside metal, so the character of adsorption surfaces is only decided by the atoms near the surface. © (2012) Trans Tech Publications.


Gao X.,Kunming University | Gao X.,Key Laboratory of Advance Materials of Yunnan Province | Gao X.,Key Laboratory of Advanced Materials of Precious Nonferrous Metals | Gan G.,Kunming University | And 15 more authors.
Key Engineering Materials | Year: 2012

Double-layered, low-voltage ZnO varistors (including layer A and layer B) have been fabricated by feeding two kinds of ZnO powders into a die using dry extrusion molding. The samples are examined by using energy dispersive X-ray spectroscopy (EDS), electron probe microanalysis (EPMA), scanning electron microscope (SEM) and DC electrical measurements. EDS and EPMA data indicate that doped elements only exists in layer A, the results of SEM indicated that secondary phases are formed at grain boundaries in layer A, not found in layer B. It is found that the electrical properties of low-voltage varistor are improved without reducing thickness and changing energy absorption capabilities. The higher nonlinearity coefficients, the lower breakdown fields and leakage currents of layered structure low-voltage ZnO varistor, as compared to those of ZnO varistor fabricated from the conventional route. The improved current-voltage properties are attributed to the band structure difference in both sides of grains, due to the different ion concentration and species in both sides of grain boundary. Double-layered structure varistor also has more simpler prepared technology than multilayer chip varistor. © (2012) Trans Tech Publications.

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