Er Jun Liang

Synthesis, microstructure and phase control of zirconium tungstate with a CO2 laser

Zirconium tungstate was successfully synthesized by rapid solidification with a CO2 laser. Scanning electron microscope observation shows that nano-threads/rods grew horizontally on the surface region and vertically in the interior. The nano-threads in the interior are composed of densely packed nano-crystallites. Raman spectroscopic study shows that the samples solidified in an orthorhombic structure when the laser scan speed was ?2?mm?s?1. This is explained by a compressive stress induced during the rapid solidification process due to a sudden drop of temperature from the molten pool to the ambient. The possibilities for tuning the strength of the compressive stress and controlling the production of different phases of ZrW2O8 are proposed. It is analysed and confirmed that the compressive stress can be effectively reduced by lowering laser scan speed. ZrW2O8 samples with cubic structure are produced with laser scan speed <2?mm?s?1.

First Principles Study on the Electronic Properties of Cr, Fe, Mn and Ni Doped β-Ga2O3

The electronic band structures, partial and total spin density of states of Cr, Fe, Mn and Ni doped β-Ga2O3 are studied. It is shown that there exists only one spin polarized state around the Fermi level for all doped β-Ga2O3. Ferromagnetism is predicted for Mn and Ni doped while spin-glass ground states are predicted for Cr and Fe doped β-Ga2O3. All doped β-Ga2O3 exhibits intermediate bands which are filled with only one spin state electrons and isolated from valence and conduction bands due to the splitting of the 3d orbitals by the potential of crystal and spin interaction

A Novel Air Cushion Press Nanoimprint Lithography

nanoimprint was developed quickly in decades because of its ultrahigh resolution, low cost, high throughput. It has demonstrated the ability to pattern 5 nm line-width and 12 inch wafer, and is one of the support technology in NGL. This paper reported a novel nanoimprint to improve the pressure uniformity with air cushion press. The chamber is sealed by a SiO2 window with an elastic ring membrane, on which the mold is fixed . Ultraviolet light solidify resist on the wafer through this window. When air in chamber bleeded the window falled and the mold is pressed into the resist. If air leading into the chamber again, the mold separate from substrate by the elastic ring membrane, then the patterns on mold are translated onto the substrate. Experiments exhibit that this nanoimprint system can replicate features with high fidelity over a large patterning area.

Synthesis and Properties of LST-X%Bi2O3 Anode Materials for Solid Oxide Fuel Cells

Ceramic systems of template explains and demonstrates how to prepare your camera-ready Ceramic systems of Bi2O3 and La-doped SrTiO3 (LST) solid mixtures La0.2Sr0.8TiO3–x%Bi2O3 (x = 0, 20, 25, 30, 35) are prepared and explored as possible anode materials for solid oxide fuel cells. It is shown that the conductivity of La0.2Sr0.8TiO3–x%Bi2O3 composites increases from 0.15 to 1.4 S cm−1 in 97%H2 +3%H2O at 800°C with increasing the content of Bi2O3. Electrochemical impedance spectra indicated that the addition of Bi2O3 into LST can significantly reduce the fuel cell’s polarization and refine the grains and increase the triple phase boundary, leading to a better performance of the fuel cells. The results suggest potential applications of LST–x%Bi2O3 composite as SOFC anode materials.

Synthesis, Thermal Expansion Properties and Raman Spectroscopic Study of Ca1-xSrxZr4P6O24 Ceramics

A simplified method with much lower time and energy costs is presented for the rapid synthesis of low thermal expansion materials of CaZr4P6O24, SrZr4P6O24 and their solid solution Ca0.5Sr0.5Zr4P6O24. The coefficients of thermal expansion of CaZr4P6O24, SrZr4P6O24 and Ca0.5Sr0.5Zr4P6O24 are measured to be -1.45×10-6, 2.1×10-6 and 0.26×10-6, respectively. Raman spectroscopic study confirms the formation of the solid solution of Ca0.5Sr0.5Zr4P6O24 though its symmetric and asymmetric stretching modes are obviously broadened with respect to those of CaZr4P6O24 and SrZr4P6O24 due to the lattice deformation by incorporation of Ca2+ and Sr2+ with different cation size. The shifts of the asymmetric stretching Raman modes and the librational/translational modes with temperature in Ca0.5Sr0.5Zr4P6O24 are between those in CaZr4P6O24 and SrZr4P6O24, suggesting a cancelling effect of Ca2+ and Sr2+ cations in the thermal expansion of Ca0.5Sr0.5Zr4P6O24.

Comparative Study on the Effective Dielectric Constant of the Graded Composites

The effective dielectric constant of the graded composites was calculated with three different methods, namely, the nonlinear differential effective dipole approximation method (NDEDA), the Maxwell-Garnette method (MGT) and the sum rule method (Sum). In each layer of the graded composites, the distribution of the dielectric constant follows a Drude form. Our numerical results show that when the number of layers N inside the graded composites increases, a gradual transition from sharp peaks to an emerging broad continuous band is clearly obtained. Moreover, the results obtained by the MGT and sum rule methods achieve a good agreement with that by the NDEDA method when N is approaching infinity.

Rapid In Situ Reactive Sintering and Properties of ZrO2-ZrW2O8 Composites

ZrO2-ZrW2O8 diphasic composites with controllable coefficients of thermal expansion (CTEs) are synthesized by rapid in-situ reactive sintering with ZrO2 and WO3 as reactants. High density of ZrO2-ZrW2O8 composites without decomposition of ZrW2O8 is obtained with Y2O3 sintering additive. The CTEs of specimen with ZrO2 to ZrW2O8 mass ratio 1:1.0, 1:1.3, 1:1.5 and 1:2.0 are measured to be about 1.20×10−6, 0.31×10−6, -0.78×10−6 and -1.13×10−6 K−1, respectively. Raman mappings demonstrate homogenous dispersions of ZrO2 and ZrW2O8 in the ZrO2-ZrW2O8 composites. In addition to the role as sintering additive, some Y3+ cations enter the lattice to substitute Zr4+ in ZrW2O8, leading to an increase in disorder and a decrease in phase transition temperature of ZrW2O8 in the composites.

Field Emission of Gallium-Doped Carbon Nanotubes

Field emission property of Ga-doped carbon nanotube (CNT) film has been studied and compared with those of un-doped, N-doped as well as B and N co-doped CNT films. It is found that the Ga-doped CNT film exhibits superior field emission property to the other films. The turn-on field for Ga-doped CNT film is well below 1.0 V/μm, lower than those for un-doped (2.22 V/μm), N-doped (1.1 V/μm), B and N co-doped (4.4 V/μm) CNT films. Its current density reaches 5000 μA/cm2 at 2.6 V/μm which is well above those for un-doped (1400 μA/cm2), N-doped (3000 μA/cm2) as well as B and N co-doped (2) CNT films at applied electric field of 5.7 V/μm. First principles calculations were carried out to obtain the binding energy and electronic nature altering of a CNT by Ga doping. It is shown that Ga-doped CNT (8,0) alters from semiconductor to intrinsic metal and a binding energy of 2.7527 eV is obtained. The field emission property can not simply be explained by the defect concentration, but can be understood by significant altering in the local density of states near the Fermi level introduced by dopants.

Improvement on Microstructure and Cracking Susceptibility of Laser-Clad Ni-Based Layers by In Situ Generation of Tantalum Carbides and Borides

Cracking is a serious problem in laser-clad hardfacing layers due to inhomogeneous distribution of coarse brittle phases and stress induced during rapid solidification. Tantalum carbides and borides which can form and precipitate at much higher temperatures are tentatively designed to inhibit the formation of the coarse brittle phases of chromium carbides and borides. It is found by XRD analysis that TaC, Ta4C3, TaB and Ta5B6 were formed in-situ and the coarse brittle phases were largely avoided in laser-clad Ni-based layers. It is also found that the formation sequence of these species is governed by their precipitation temperature instead of the rule determined by the standard free energy of formation. The formation of the chromium carbides and borides is inhibited due to the priority of formation of tantalum carbides and borides during rapid solidification. SEM and penetration visualization examinations show that the microstructure is markedly refined and the cracking susceptibility is significantly reduced by this method. The microhardness of the layers maintains at about 800 Hv.

Study on Synthesis and Properties of the Hafnium Tungstate by CO2 Laser

The crystal structure of hafnium tungstate displays unusual property of isotropic negative thermal expansion in a wide temperature range which brings about a number of important potential applications. In this work, densely packed hafnium tungstate blocks are rapid synthesized by CO2 laser. The result of XRD and Raman spectra show that the samples contain single cubic phase of α-HfW2O8 with space group P213. The SEM observations show that the sample is composed of nano-rods which grow horizontally on the surface and in the interior. The nano-threads in the interior are composed of densely packed nano-crystallites.