Search results for "ESA"
showing 10 items of 11914 documents
Electrical and thermomechanical properties of CVI- Si3N4 porous rice husk ash infiltrated by Al-Mg-Si alloys
2017
Abstract The effect of following processing parameters on the electrical and thermomechanical properties of Al/Si3N4 deposited silica composites was investigated using the Taguchi method and analysis of variance (ANOVA): infiltration temperature and time, atmosphere, effect of Si3N4 coating, porosity content in the preforms, and magnesium content in the alloy. The contributions of each of the parameters to modulus of elasticity, electrical resistivity, coefficient of thermal expansion (CTE), and thermal diffusivity of the resulting composites were determined. The maximum modulus of elasticity and electrical resistivity of obtained composites were 265 GPa, and 1.37 × 10−3 Ω m, respectively. …
Static and dynamic structure of $ZnWO_4$ nanoparticles
2011
Abstract Static and dynamic structure of ZnWO 4 nanoparticles, synthesized by co-precipitation technique, has been studied by temperature dependent x-ray absorption spectroscopy at the Zn K-edge and W L 3 -edge. Complementary experimental techniques, such as x-ray powder diffraction, Raman and photoluminescence spectroscopies, have been used to understand the variation of vibrational, optical, and structural properties of nanoparticles, compared to microcrystalline ZnWO 4 . Our results indicate that the structure of nanoparticles experiences strong relaxation leading to the significant distortions of the WO 6 and ZnO 6 octahedra, being responsible for the changes in optical and vibrational …
Ab initio calculations of structural, electronic and vibrational properties of BaTiO3 and SrTiO3 perovskite crystals with oxygen vacancies
2020
The first-principles (ab initio) computations of the structural, electronic, and phonon properties have been performed for cubic and low-temperature tetragonal phases of BaTiO3 and SrTiO3 perovskite crystals, both stoichiometric and non-stoichiometric (with neutral oxygen vacancies). Calculations were performed with the CRYSTAL17 computer code within the linear combination of atomic orbitals approximation, using the B1WC advanced hybrid exchange-correlation functional of the density-functional-theory (DFT) and the periodic supercell approach. Various possible spin states of the defective systems were considered by means of unrestricted (open shell) DFT calculations. It was demonstrated that…
Experimental studies on uniaxial and echibiaxial tensile tests applied to plastic materials sheets
2019
Abstract The main objective of this paper is to determine the behavior of few plastic materials using two different type of tests. We use classical uniaxial tensile test to determine the most important mechanical and elastic characteristics, such as: yield stress, Young modulus, tangent modulus, maximum stress and maximum strain and to plot engineering stress vs. engineering strain curve for these materials. The second test, that was used in this study, was echibiaxial tensile test on the spherical punch. This test was used to determine maximum breaking force and, of course maximum displacement of specimen on punch direction and others few important characteristics, such as: major and minor…
Raman characterization of Pb2Na1−xLaxNb5−xFexO15 and Pb0.5(5−x)LaxNb5−xFexO15 (0≤x≤1) solid solutions
2011
Abstract The ferroelectric compounds Pb 2 Na 1− x La x Nb 5− x Fe x O 15 and Pb 0.5(5− x ) La x Nb 5− x Fe x O 15 (0≤ x ≤1) with the tungsten bronze type structure have been investigated using Raman spectroscopy. The evolution of the spectra as a function of composition at room temperature is reported. In the frequency range 200–1000 cm −1 three main A 1 phonons around 240 ( υ 1 ), 630 ( υ 2 ) and 816 ( υ 3 ) cm −1 were observed. The broadening of the Raman lines for high values of x originates from a significant structural disorder. This is in good agreement with the relaxor character of these compositions. The lowest-frequency part of the spectra, below 180 cm −1 , reveals a structural ch…
Integral imaging with Fourier-plane recording
2017
Integral Imaging is well known for its capability of recording both the spatial and the angular information of threedimensional (3D) scenes. Based on such an idea, the plenoptic concept has been developed in the past two decades, and therefore a new camera has been designed with the capacity of capturing the spatial-angular information with a single sensor and after a single shot. However, the classical plenoptic design presents two drawbacks, one is the oblique recording made by external microlenses. Other is loss of information due to diffraction effects. In this contribution report a change in the paradigm and propose the combination of telecentric architecture and Fourier-plane recordin…
Lattice sites of diffused gold and platinum in epitaxial ZnSe layers
2000
Abstract The lattice location of diffused gold and platinum in zinc selenide (ZnSe) epitaxial layers was studied using the Rutherford backscattering (RBS) channeling technique. Thin Au and Pt films were evaporated onto ZnSe samples. The Au/ZnSe samples were annealed at 525°C and the residual Au film was removed by etching. Channeling angular scan measurements showed that about 30% of Au atoms were close to substitutional site (displaced about 0.2 A). In the case of the Pt/ZnSe samples the annealing temperatures ranged from 600°C to 800°C. The Pt minimum yields along 〈1 0 0〉 direction were close to the random value, varying from 80% to 90%. The measured Pt angular scans along 〈1 0 0〉 and 〈1 …
Influence of Sr addition on structural, dielectric and Raman properties of Na0.5Bi0.5TiO3ceramics
2016
ABSTRACTLead free (Na0.5Bi0.5)1-xSrxTiO3 (x = 0, 0.01 and 0.02) ceramics were produced by a conventional solid-state sintering method. X-ray diffraction analysis shows that the obtained samples possess the perovskite structure with rhombohedral symmetry. The microstructure study shows a dense structure, in agreement with the relative density (above 97%). Dielectric analysis revealed the diffuse character of the electric permittivity anomalies and their shift to a lower temperature range after Sr doping of NBT. The Raman spectra are similar for all samples in agreement with the X-ray diffraction data. The possible origin of the observed effects was discussed.
Raman spectra and anomalies of dielectric properties and thermal expansion of lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramics
2016
ABSTRACTThermal expansion, Raman and dielectric properties of the lead-free (1−x)Na0.5Bi0.5TiO3-xSrTiO3 (x = 0, 0.08 and 0.1) ceramic solid solutions, fabricated by the conventional solid-state reaction method, were investigated. The Sr-doping results in an increase of the dielectric permittivity, broadening of the permittivity maximum, enhancement of the relaxation near depolarization temperature, broadening of the Raman bands and shift of all anomalies toward lower temperatures. The observed effects are attributed to an increase of the degree of cationic disorder and enhancement of the relaxor-like features. Anomalies in the thermal expansion strain were observed at the temperatures corre…
Dielectric, thermal and Raman spectroscopy studies of lead-free (Na0.5Bi0.5)1−xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics
2016
ABSTRACTLead-free (Na0.5Bi0.5)1−xSrxTiO3 (x = 0, 0.04 and 0.06) ceramics with relative densities above 97% were prepared by solid-state synthesis process. Their dielectric, thermal and Raman properties were studied. X-ray diffraction analysis shows perovskite structure with rhombohedral symmetry at room temperature. Sr doping of Na0.5Bi0.5TiO3 (NBT) results in an increase of the dielectric permittivity, diffusing of the permittivity maximum and its shift toward lower temperatures. The temperature of the rhombohedral–tetragonal phase transition indicated by the differential scanning calorimetry (DSC) peak and relaxational dielectric anomaly near the depolarization temperature are also shifte…