Modelling and optimization of laminated adaptive shells of revolution

In this paper two shell finite element models are presented for the structural analysis of composite laminated piezoelectric shells. One is an axisymmetric conical frustum with two nodal rings and the other is a conic shell panel with eight nodes. Both models are based in a mixed laminated theory that combines a higher order shear deformation theory for the mechanical displacement field with a layerwise representation with linear functions for the electric potential through each piezoelectric layer. In order to obtain the optimal design sensitivities analysis and optimization techniques based in the nonlinear mathematical programming are used. The design objectives can be the minimization of the deformed structure or the maximization of the natural fundamental frequency and the design variables are the electric potential difference applied to the actuators or the ply thicknesses among others.     

Parametric studies of multi-material laser densification

Fabrication of multi-material components via a laser-assisted layer-by-layer fabrication process has been numerically simulated and analyzed using a three-dimensional thermo-mechanical model. Effects of the chamber preheating temperature, laser scanning rate, initial porosity and thickness of each powder layer on the out-of-plane warping and residual thermal stresses of a nickel/porcelain workpiece have been investigated. It is found that warping and residual thermal stresses of the laser-densified multi-material workpiece are more sensitive to the chamber preheating temperature and the thickness of each powder layer than to the laser scanning rate and the initial porosity of the powder layer. The major mechanism responsible for these phenomena is identified to be related to the change of the temperature gradient induced by these laser processing parameters.     

Non-Local Theory Solution for an Anti-Plane Shear Permeable Crack in Functionally Graded Piezoelectric Materials

In this paper, the non-local theory solution of a Griffith crack in functionally graded piezoelectric materials under the anti-plane shear loading is obtained for the permeable electric boundary conditions, in which the material properties vary exponentially with coordinate parallel to the crack. The present problem can be solved by using the Fourier transform and the technique of dual integral equation, in which the unknown variable is the jump of displacement across the crack surfaces, not the dislocation density function. To solve the dual integral equations, the jump of the displacement across the crack surfaces is directly expanded in a series of Jacobi polynomials. From the solution of the present paper, it is found that no stress and electric displacement singularities are present near the crack tips. The stress fields are finite near the crack tips, thus allows us to use the maximum stress as a fracture criterion. The finite stresses and the electric displacements at the crack tips depend on the crack length, the functionally graded parameter and the lattice parameter of the materials, respectively. On the other hand, the angular variations of the strain energy density function are examined to associate their stationary value with locations of possible fracture initiation.     

离子束溅射制备Si／Ge多层膜研究

采用离子束溅射方法在Si衬底上制备Si／Ge多层膜，通过改变生长温度、溅射速率等因素得到一系列Si／Ge多层膜样品；通过X射线衍射、Raman散射等表征方法研究薄膜结构与生长条件的关系。在小束流（10mA）、室温条件下制备出界面清晰、周期完整的Si／Ge多层膜。     

Photoluminescent characterization of KNbO3:Eu

In this study, the photoluminescence (PL) spectra of europium-doped potassium niobate (KNbO₃) crystallites prepared by a vibrating milled solid-state reaction method were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical spectral analysis (luminescence excitation, emission spectra and time-resolved spectra) were used to characterize the KNbO₃:Eu³⁺ powders. The results of the XRD revealed that the powders remained as a single orthorhombic structure at doping concentrations below 3 mol%. A second phase of EuNbO₄ begins to appear at 5 mol%. The ⁵D₀–⁷F₁ (593 nm) and ⁵D₀–⁷F₂ (614 nm) emission characteristics of Eu³⁺ appear at a quenching concentration of above 3 mol%. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of a Eu:KNbO₃ host excited at λ_ex = 400 nm and λ_ex = 466 nm wavelengths, both presented a red-shift when increasing the Eu³⁺ ion doping. The lifetime of the Eu³⁺ ion decreased as the doping concentration was increased from 1 to 7 mol%.     

Sr and Ba substitution in charge ordered Pr0.5Ca0.5MnO3: Sharp steps in the magnetic and transport properties for a narrow composition range

The magnetic and transport properties of Pr_0.5Ca_0.5−xA_xMnO₃ (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr (x = 0.07–0.10) and Ba (x = 0.01–0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.     

Effect of sintering condition on microstructure and dielectric properties of BSTN composite ceramics

The effect of sintering condition on the phase composition, microstructure and dielectric properties of barium strontium titanate niobate (BSTN) composite ceramics, in which the perovskite phase and the tungsten bronze phase coexisted, was investigated by XRD, SEM and LCZ Meter. The results show that more Sr²⁺ ions dissolved from the grain boundaries into the crystal lattice of the pervoskite phase and the tungsten bronze phase, especially, into the lattice of the pervoskite phase with the increasing of sintering temperature and sintering time, respectively. So the Curie temperature point decreases with the increasing of sintering temperature. The crystal growth rate of the tungsten bronze phase is higher than that of the perovskite phase in BSTN composite ceramics as the sintering temperature increases. The reasonable sintering temperature is about 1275 °C for BSTN composite ceramics. The activation energy to setting up polarization in BSTN composite ceramics increases with the increase of the applied frequency.     

Preparation of silver nanoparticles via a non-template method

Silver nanoparticles have been prepared by a non-template method. Silver nitrate can be easily decomposed into silver nanosized materials. Small nanoparticles (less than 2 nm) can be formed in aqueous solution. Larger silver particles of about 100 nm can be formed in ethanol solution. By rationally adjusting the experimental conditions we finally obtain silver particles of about 20 nm with a relatively narrow distribution in ethanol solution. Differing from the previous reports, we find that silver nanoparticles can be formed by direct decomposition of AgNO₃ under UV light irradiation. No catalyst like TiO₂ is needed at all. We believe that it is a further step to precede the preparation of silver nanometer sized materials.     

Plasma etching of high-k and metal gate materials

Etching characteristics of high-k dielectric materials (HfO₂) and metal electrode materials (Pt, TaN) have been studied in high-density chlorine-containing plasmas at pressures around 10 mTorr. The etching of HfO₂ was performed in BCl₃ without rf biasing, giving an etch rate of about 5 nm/min with a high selectivity of >10 over Si and SiO₂. The etching of Pt and TaN was performed in Ar/O₂ with high rf biasing and in Ar/Cl₂ with low rf biasing, respectively, giving a Pt etch rate of about several tens nm/min and a TaN etch rate of about 200 nm/min with a high selectivity of >8 over HfO₂ and SiO₂. The etched profiles were outwardly tapered for Pt, owing to the redeposition of etch or sputter products on feature sidewalls, while the TaN profiles were almost anisotropic, probably owing to the ion-enhanced etching that occurred.