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【资源】哲学杂志89卷1－9期的有关玻璃的文章
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1 Determination of the thickness and optical constants of amorphous Ge–Se–Bi thin films A. Dahshana* and K.A. Alyb aDepartment of Physics, Faculty of Science, Suez Canal University, Port Said, Egypt; bPhysics Department, Faculty of Science, Al-Azhar University, Assiut Branch, Assiut, Egypt (Received 18 July 2008; final version received 18 February 2009) The effect of varying bismuth concentration on the optical constants of amorphous Ge20Se80[1]xBix (where x¼0, 3, 6, 9 and 12 at%) thin films prepared by thermal evaporation has been investigated. The transmission spectra T([1]) of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. An analysis proposed by Swanepoel [J. Phys. E: Sci. Instrum. 16 (1983) p.1214], based on the use of the maxima and minima of the interference fringes, was applied to derive the real and imaginary parts of the complex index of refraction and also the film thickness. Increasing bismuth content was found to affect the refractive index and extinction coefficient of the Ge20Se80[1]xBix films. Optical absorption measurements show that the fundamental absorption edge is a function of composition. With increasing bismuth content, the refractive index increases while the optical band gap decreases. Keywords: amorphous; thin films; optical transmission http://www.sciencenet.cn/bbs/download.aspx?id=2009429115131400 (文件大小:442k) 2 Optical constants of quaternary Ge–As–Te–In amorphous thin films evaluated from their reflectance spectra K.A. Aly* Faculty of Science, Department of Physics, Al Azhar University, Assiut, Egypt (Received 31 March 2008; final version received 4 March 2009) Thin films of amorphous Ge9As20Te71[1]xInx with different compositions (x¼0, 3, 6 and 9 at. %) were obtained by deposition onto glass substrates by thermal evaporation. The reflection spectra, R([1]), of the films were obtained in the spectral region from 400 to 2500 nm. A straightforward analysis proposed by Ruiz-Perez et al., based on the use of the maxima and minima of the interference fringes, has been applied to derive the real and imaginary parts of the complex index of refraction, the thickness and the thickness variation of the studied films. Increasing In content is found to affect the refractive index and the extinction coefficient of the films. Optical absorption measurements were used to obtain the fundamental absorption edge as a function of composition. With increasing In content, the refractive index decreases, whereas the optical band gap, Eg, increases.The relationship between Eg and the chemical composition of the Ge9As20Te71[1]xInx system is discussed in terms of the cohesive energy, the average heat of atomization, Hs, and the average coordination number, Nr. Keywords: optical constant; amorphous thin film; band gap; absorption edge http://www.sciencenet.cn/bbs/download.aspx?id=2009429115218369 (文件大小:281k) 3 Structural analysis of rapidly solidified Mg–Cu–Y glasses during room-temperature embrittlemen D.I. Uhlenhauta, F.H. Dalla Torrea, A. Castelleroay, C.A.P. Gomezb, N. Djourelovb, G. Kraussc, B. Schmittd, B. Pattersond and J.F. Lo¨ fflera* aLaboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland; bDepartment of Subatomic and Radiation Physics, Ghent University, 9000 Ghent, Belgium; cLaboratory of Crystallography, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland; dSwiss Light Source, Paul Scherrer Institute, 5232 Villigen-PSI, Switzerland (Received 31 July 2008; final version received 1 November 2008) The structural changes of rapidly-quenched amorphous Mg–Cu–Y alloys during time-dependent room-temperature embrittlement were investigated. A continuous reduction in enthalpic content with time, corresponding to a loss in free volume, and radial atomic distances obtained from synchrotron X-ray diffraction experiments imply an overall reduction in volume. Two distinct lifetimes were found by positron annihilation lifetime spectra, with the longer-lifetime component (attributed to areas of larger free volume) vanishing after an ageing time corresponding roughly to the time of embrittlement. Coincidence Doppler broadening suggests that the immediate environment of the annihilation sites is not altered during ageing. The mechanical behaviour correlates with the structural changes in the alloy. The densification observed is assumed to influence the sharp ductile-to-brittle transition in these Mg-based glasses, and the abrupt change in bending ductility is found to result from disappearing large free volume. Keywords: metallic glass; relaxation; embrittlement; structure; mechanical properties http://www.sciencenet.cn/bbs/download.aspx?id=200942911541775 (文件大小:501k) 4 Molecular dynamics simulation of diffusion in supercooled Cu–Zr alloys M.I. Mendelev*, M.J. Kramer, R.T. Ott and D.J. Sordelet Materials and Engineering Phys. Program, Ames Laboratory, Ames, IA 50011, USA (Received 2 July 2008; final version received 16 October 2008) Molecular dynamics (MD) simulations of diffusion in Cu–Zr alloys in their liquid and supercooled liquid states were performed using a recently developed Finnis– Sinclair many-body interatomic potential. To help assess how well the interatomic potential describes the energetics of the Cu–Zr system, the liquid structure determined by MD simulations was compared with wide-angle X-ray scattering measurements of the liquid structure for a Cu64.5Zr35.5 alloy. Diffusion was examined as a function of composition, pressure and temperature. The simulations reveal that the diffusion exhibits strong compositional dependence, with both species exhibiting minimum diffusivities at [1]70% Cu. Moreover, the MD simulations show that the activation volumes for Zr and Cu atoms exhibit a maximum near 70% Cu. Evidence is obtained that the glass transition temperature also changes strongly with composition, thereby contributing to the diffusion behaviour. The relationship between this minimum in diffusion and the apparent best glass-forming composition in the Cu–Zr system is discussed. Keywords: diffusion; liquid alloys; diffraction; molecular dynamic simulations http://www.sciencenet.cn/bbs/download.aspx?id=2009429115442432 (文件大小:299k) 5 Crystallization kinetics of the TeO2–BaO glass system E.R. Shaabana*, Y.B. Saddeeka and M. Abdel Rafeab aFaculty of Science, Physics Department, Al-Azhar University, P.O. Box 71452, Assiut, Egypt; bElectronic Materials Department, Mubarak City for Scientific and Technological Applications, Institute of Advanced Technology and New Materials, Zweil St., P.O. Box 21934, New Borg E1-Arab City, Alexandria, Egypt (Received 15 May 2008; final version received 17 October 2008) Tellurite glasses of the system (100–x)TeO2–xBaO, with x¼05, 10, 15 and 20 wt%, have been prepared and studied by differential scanning calorimetry (DSC). The crystallization kinetics of the glasses were investigated under nonisothermal conditions, applying the formal theory of transformations for heterogeneous nucleation to the experimental data obtained by DSC, using continuous-heating techniques. In addition, from the dependence of the glasstransition temperature (Tg) on heating rate, the activation energy for the glass transition was derived. Similarly, the activation energy of the crystallization process was determined and the crystallization mechanism characterized. The thermal stability of these glasses are considered in terms of the characteristic temperatures, Tg and Tin (the onset temperature of crystallization), via [1]T¼Tin[1]Tg and a kinetic parameter K(Tg). The results confirm that thermal stability decreases with increasing BaO content. The phases into which the glass crystallizes have been identified by X-ray diffraction. Diffractograms of the transformed material indicate the presence of microcrystallites of [1]-TeO2, -TeO2 and BaTeO3 in the remaining amorphous matrix. Keywords: tellurite glasses; thermal analysis; crystallization kinetics; glass structure; DSC http://www.sciencenet.cn/bbs/download.aspx?id=200942911564385 (文件大小:244k) 6 Effect of B2O3 on the structure and properties of tungsten–tellurite glasses Y.B. Saddeek* Faculty of Science, Physics Department, Al-Azhar University, Assiut 71542, Egypt (Received 25 June 2008; final version received 23 October 2008) The elastic properties and Debye temperatures of xB2O3–70TeO2–(30–x)WO3, (0[1]x[1]30 mol%) glasses have been investigated using sound velocity measurements at 4 MHz. Ultrasonic and thermal parameters, combined with the results of IR spectroscopic analyses, were employed to explore the effect of B2O3 on the structure of tungsten–tellurite glasses. According to IR analysis, there is competition between WO6 and TeO4 units to form BO4 units, and the vibrations of the tellurite structural units are shifted towards lower wavenumbers on the formation of non-bridging oxygens. It is assumed that B2O3 acts as a modifier by decreasing the glass-transition temperature Tg and increasing both the thermal stability and glass formation range of the tellurite glasses. The change in density and molar volume with B2O3 content reveals that the borate units are less dense than the tellurite structural units. The observed compositional dependence of elastic moduli is interpreted in terms of the effect of B2O3 on the coordination number of the tellurite units. A good correlation was observed between experimentally determined elastic moduli and those computed with theMakishima–Mackenzie model. Keywords: tellurite glasses; borate glasses; elastic properties; IR analysis PACS;43.35.Ae; 61.43.Fs; 62.20.Dc; 78.30.Ly http://www.sciencenet.cn/bbs/download.aspx?id=2009429115643916 (文件大小:252k) [ Last edited by hslining on 2009-9-10 at 15:01 ] |
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