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1.
AsTe glasses have been investigated for determining the molecular mechanisms of glass formation and of crystallization. Stable and homogeneous bulk glasses are prepared throughout the range of concentration from 20 to 65 at % As, by using an improved quenching method. GFA (glass-forming ability) is determined with respect to the rate of cooling. Density, microhardness, Tg and ΔCp at Tg are measured in the whole range of glass formation. Finally a quantitative analysis of the kinetics of crystallization is carried out. It appears that most properties which involve molecular motions exhibit anomalies for As40 Te60 composition (As2Te3 is the unique definite compound of the system). So GFA shows a sharp depression for this critical composition; similarly enthalpy and kinetics of crystallization are drastically modified at As40Te60. For Te-rich glasses, crystallization occurs at low temperature by homogeneous nucleation with a small energy of activation. For As-rich glasses, crystallization occurs at much higher temperatures. Above 200°C it is controlled by growth with an high activation energy which indicates deep rearrangements of the relative positions of the atoms by chemical diffusion. A coherent analysis of all the data is developed which shows that important differences of local order exist between amorphous and crystalline states and also between the two well-distinct types of glasses we are dealing with. The aim of paper II is to determine these differences from diffraction data.  相似文献   

2.
The structure of Al83Cu17 and Al88Si12 liquid eutectic alloys has been studied using the X-ray diffraction (XRD) and reverse Monte-Carlo (RMC) methods. The total and partial structure factors and pair correlation functions as well as structure parameters obtained therefrom have been analyzed. Chemically ordered Al–Cu groups significantly effect the structure in Al83Cu17, while a tendency to chemical ordering between atoms of an unlike kind is negligible in Al88Si12.  相似文献   

3.
The growth and structure of (1-1.5)-μm-thick Pb1?x Mn x Te(Ga)(x = 0.06) films with 0.4?0.9 at % of gallium, grown on BaF2(111) and Pb1?x Sn x Te (x = 0.2) (100) substrates by molecular beam epitaxy, have been investigated. It is established that the films are crystallized into an fcc structure, and their growth planes are (111) and (100), according to the substrate orientation. The optimal conditions for obtaining high-resistivity photosensitive p-and n-type films with a perfect crystal structure (W 1/2 = 80″?100″) have been determined.  相似文献   

4.
S. Rada  A. Dehelean  E. Culea 《Journal of Non》2011,357(16-17):3070-3073
Glasses in the xEu2O3·(100-x)[4TeO2·PbO2] system where 0  x  50 mol% have been prepared using the melt quenching method. The influence of europium ions on the structure of lead–tellurate glasses has been investigated using density measurements, FTIR and UV–VIS spectroscopy. Structural changes produced by increasing the rare earth concentration were followed.The europium and lead ions show a preference towards [TeO3] structural units causing a deformation of the TeOTe linkages. Structural changes inferred by analyzing the band shapes of IR spectra revealed that the increase of the Eu+ 3 content causes the intercalation of [EuOn] entities in the [TeO4] chain network. The excess of oxygen can be supported into the glass network by the formation of [PbOn] and [EuOn] structural units.The UV–VIS spectroscopy data show that europium ions enter the glass matrix in the Eu2+ and Eu3+ valence states, the last being predominant in the studied glasses. The Pb+ 2 ions produce strong absorption in the ultraviolet domain.  相似文献   

5.
Differential scanning calorimetry measurements were used to study crystallization in the SeyTe(1 ? y) glassy system under non-isothermal conditions. The examined compositions were y = 0.1, 0.2 and 0.3. The crystallization kinetics was described in terms of the Johnson–Mehl–Avrami nucleation–growth model. It was found that with the addition of tellurium into the selenium matrix the apparent activation energy of the crystallization process monotonically increases and, more importantly, the parameter of the JMA model m decreases. This change in the crystallization mechanism was interpreted as a gradual crossover from surface to bulk process. Both processes are competitive and proceed simultaneously in glasses with low tellurium content, while in the case of increased Te content the surface crystallization mechanism recedes. The transition between mechanisms was discussed in terms of changes in molecular structure of the material.  相似文献   

6.
The new crystal and molecular structures of a less common hydrated calcium L(–)-malate (calcium (2S) 2-hydroxybutanedioate trihydrate) Ca(C4H4O5)3H2O, are reported. X-ray crystallographic data are as follows: a = 6.6460(3) Å, b = 8.3795(3) Å, c = 8.2707(4) Å, = 112.640(2)°, V = 425.1(4) Å3, space group P21 (No. 4), Z = 2, D calc = 1.767 g cm–3. The calcium ion coordination number is seven. One of the three water molecules present in the unit cell is less strongly bound, only interacting with a calcium ion. In aqueous or hydroalcoholic solution, both di- and trihydrated species crystallize simultaneously.  相似文献   

7.
The local structure of phosphorus and silicon in the molten CaO–SiO2–PO2.5 slag system was investigated by magic angle spinning nuclear magnetic resonance (MAS-NMR). The 31P MAS-NMR spectra revealed that phosphorus was present primarily as the monophosphate complex ion PO43?, with a small amount of diphosphate ion also present. Their relative ratio to total phosphorus was independent of the phosphate concentration of the sample. In the case of the 29Si MAS-NMR, the mean number of the non-bridging oxygen atoms associated with tetrahedrally coordinated silicon decreased as the phosphate concentration increased at a fixed CaO/SiO2 ratio. This indicates that the nonbridging oxygen atoms around the silicon were replaced by bridging oxygen atoms around the phosphorus as the phosphate concentration in the samples increased.To elucidate the basicity dependence of the structure of slag, the relationship between the structure and optical basicity was also investigated. The relative ratio of Qn (Qn means the silicon atoms tetrahedrally bonded with “n” number of bridging oxygen atoms) strongly depends on the optical basicity. These optical basicity dependencies of the structures of phosphorus and silicon can be explained clearly by the basicity equalization concept (Duffy and Ingram, 1976) [12].  相似文献   

8.
The complicated structural speciation in boroaluminosilicate glasses leads to a mixed network former effect yielding nonlinear variation in many macroscopic properties as a function of chemical composition. Here we study the composition–structure–property relationships in a series of sodium boroaluminosilicate glasses from peralkaline to peraluminous compositions by substituting Al2O3 for SiO2. Our results reveal a pronounced change in all the measured physical properties (density, elastic moduli, hardness, glass transition temperature, and liquid fragility) around [Al2O3]–[Na2O] = 0. The structural origin of this change is elucidated through nuclear magnetic resonance analyses and topological considerations. Furthermore, we find that addition of 1 mol% Fe2O3 exerts a complicated impact on the measured properties.  相似文献   

9.
The electron spin resonance of Mn has been studied in AsxSe100?x with 0 ? x ? 70 and AsxTe100?x with 40 ? x ? 70. All samples, except those with x < 20 in AsxSe100?x, exhibit six hyperfine lines centered at g = 4.3. A g = 2.0 line is observed in As–Se with largely scattered linewidth by samples, but not in As–Te unless oxygen contamination is included in the samples. The g = 4.3 line in As–Se is closely related to a formation of As2Se3-type layer structure and interpreted as being caused by Mn situated at the interlayer position and surrounded by four Se atoms in an arrangement of rhombic symmetry. In As–Te, a similar model by four Te atoms is valid in composition near As2Te3, but the surrounding Te is replaced by As as As content increases. The g = 2.0 line is concluded to come from phase-separated antiferromagnetic particles of Mn–O and MnSe. The linewidth is scattere by differences in the relative amounts of the two kinds of particles and in particle size.  相似文献   

10.
To investigate the effects of tellurium (Te) deposition rate on the properties of Cu–In–Te based thin films (Cu/In=0.30–0.31), the films were grown on both bare and Mo-coated soda-lime glass substrates at 200 °C by co-evaporation using a molecular beam epitaxy system. The microstructural properties were examined by means of scanning electron microscopy and X-ray diffraction. The crystalline quality of the films was improved with increase in the deposition rate of Te, and exhibited a single CuIn3Te5 phase with a highly preferred (1 1 2) orientation. Te-deficient film (Te/(Cu+In)=1.07) grown with a low Te deposition rate showed a narrow bandgap of 0.99 eV at room temperature. The solar cell performance was affected by the deposition rate of Te. The best solar cell fabricated using CuIn3Te5 thin films grown with the highest deposition rate of Te (2.6 nm/s) yielded a total area (0.50 cm2) efficiency of 4.4% (Voc=309 mV, Jsc=28.0 mA/cm2, and FF=0.509) without light soaking.  相似文献   

11.
Compositional dependence of optical parameters in thermally evaporated amorphous Se80.5Bi1.5Te18 ? yAgy (for y = 0, 1.0, 1.5 and 2.0 at.%) quaternary thin films has been studied using well established Swanepoel method. The optical properties like, refractive index (n), extinction coefficient (k), absorption coefficient (α) and optical band gap (Eg) have been determined from the transmission spectra in the spectral range from 500 to 2500 nm. The optical band gap (Eg) has been estimated by using Tauc's extrapolation method and is found to increase with an increase in the Ag concentration. Present study shows that the refractive index, extinction coefficient and optical band gap increase with the increasing Ag content which is in agreement with the earlier studies. While the increase in the refractive index with Ag content over the entire spectral range can be attributed to the increased polarizability of larger Ag atomic radius (153 pm) compared to the Te atomic radius (135 pm), the increase in the optical band gap with increasing Ag concentration is correlated to an increase in the cohesive energy and decrease in the electronegativity of the films under study. The dielectric constant and optical conductivity (σ) of the thin films under study are also found to increase with the Ag concentration.  相似文献   

12.
Glasses in the (Er2O3)x·(B2O3)(60 ? x)·(ZnO)40 system (0  x  15 mol%) have been prepared by the melt quenching technique. X-ray diffraction, FTIR spectroscopy, UV-VIS spectroscopy and ab initio calculations studies have been employed to study the role of Er2O3 content on the structure of the investigated glass system.X-ray diffraction and infrared spectra of the glasses reveal that the B–O–B bonds may be broken with the creation of new non-bridging oxygen ions facilitating the formation of Er–O–B linkages. The excess of oxygen can be accommodated in the network by the conversion of sp2 planar [BO3] units to the more stable sp3 [BO4] tetrahedral structural units. The linkages of the [BO4] structural units can polymerize in [B3O9]? 9 cyclic trimeric ions which will produce the ErBO3 crystalline phase. An increase of the efficiency corresponding to the 4I15/2 state to 4I11/2 state (4f–4f) transitions of Er+ 3 ions was observed for the erbium oxide richest glasses.Ab initio calculations on the structure of the matrix network show the thermodynamic instability of the [BO4], [ZnO4] and [Zn4O] structural units. Formation of three-coordination oxygens was necessary to compensate shortage of oxygens from zinc ions.  相似文献   

13.
Single crystals of a symmetrically substituted molecule, [Zn(C3N6H6)(H2O)0.5Cl2] (C3N6H6)(H2O)(1), have been obtained. The crystal structure of 1 shows the existence of novel layered type supramolecular structure constructed by dumbbell-shape coordinated Zn moleculeand one 2,4,6-triamine-s-triazine ligand. Crystallographic data for 1: monoclinic system, space group: C2/c, a = 12.2532(9), b = 13.8606(10), c = 18.3603(13) Å, = 99.7860(10), V = 3072.9(4) Å3 and Z = 8, Dc = 1.758 Mg/m3, R1 = 0.0518. The fluorescent property of 1 has also been studied. The luminescent property of 1 attributable to both ligand * transitions and electronic transfer of ZnII O transitions.  相似文献   

14.
The main aim of the study presented in this paper is the investigation of the structure of (As2S3)100?x(SbSI)x and (As2Se3)100?x(SbSI)x (0  ×  40) glasses by Raman spectroscopy and X-ray methods, also the nature of the crystalline inclusions which arise up in their matrix at heat treatment. We have found that in conditions of continuous heating in the interval “glassforming temperature–crystallization temperature” a crystallization with predominant mechanism of stable phase SbSI separation is taking place. The formation mechanism of crystalline inclusions of antimony sulphoiodide in glass matrix is discussed in the light of our results. It was established that all investigated glasses have a nano-heterogeneous structure.  相似文献   

15.
A novel heteronuclear complex, [NdZn2L6(NO 3)(phen)2] (HL = -methylacrylic acid, phen = 1,10-phenanthroline), was synthesized and characterized by elemental analysis, infrared absorption spectra (IR) and its molecular structure was also determined by X-ray structure analysis. The title complex contains a discrete trinuclear ZnNdZn molecule bridged by carboxylate groups between Zn and Nd ions and crystallizes in space group P¯1 with the cell dimensions: a = 13.601(3) Å, b = 16.859(2) Å, c = 12.575(2) Å, = 110.09(1), = 112.21(1), = 81.10(2).  相似文献   

16.
17.
《Journal of Non》2006,352(52-54):5618-5632
A continuous network model of xWO3–(1  x)TeO2 glasses is developed, based on quantum-chemical calculation and Raman spectra analysis, in order to relate the structural and vibrational properties with glass composition. The tungstate–tellurite glass network is shown to be formed mainly by structural units of three types, TeO4 trigonal bipyramids, OTeO2 trigonal pyramids, and WO6 octahedra with OW double bonds. Most of the W atoms are found to be incorporated into single OWO5 octahedra, with no more than several percents of these atoms occurring in 2[OWO5] paired tungstate centers. The structural and vibrational properties of tungstate–tellurite glasses of several compositions are analyzed by application of the model and a novel interpretation of the Raman spectra is suggested.  相似文献   

18.
K.A. Aly 《Journal of Non》2009,355(28-30):1489-1495
Amorphous Ge10Se90?xTex (with x = 0, 5, 10 and 15 at.%) thin films were prepared by thermal evaporation method. The optical transmission spectra of these films were measured in the wavelength range of 500–2500 nm in order to drive the refractive index and the absorption coefficient of these films. Applying the analytical expressions proposed by Swanepoel, enabling the calculations of optical constants of thin films with non-uniform thickness with high accuracy. Furthermore, the dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. It was found that, the mechanism of the optical absorption follows the rule of the allowed non-direct transition. The optical band gab, Eg, and the oscillator energy, Eo, decrease while the dispersion energy, Ed, increases by increasing Te content. The relationship between the obtained results and the chemical compositions of the Ge10Se90?xTex thin films were discussed in terms of the chemical bond approach, the excess of Se–Se homopolar bonds and the cohesive energy (CE).  相似文献   

19.
This research aims to investigate and compare the structural and the morphological properties of both lithium disilicate glasses doped with copper oxide and their glass–ceramic derivatives. Density measurements were measured for all samples by Archimedes method at room temperature. Differential scanning calorimetric analysis was used to determine the glass transition temperature (Tg) and crystallization temperature (Tc) for all glasses. The glass transition temperature was observed to decrease with increasing CuO concentration indicating the formation of non-bridging oxygen bonds in the glass network. X-ray analysis patterns reveal the appearance of crystalline lithium metasilicate phase as the main phase within the glass–ceramic derivatives, and their crystallite sizes were observed to decrease as the CuO increased. Experimental infrared absorption data indicate the existence of characteristic vibrational bands due to structural building SiO4 units in resemblance to the same vibrations observed from traditional crystalline silicates. Scanning electron microscopic investigations show the vitreous nature for lithium disilicate glasses and the distinct crystalline morphological features for the corresponding glass–ceramic derivatives.  相似文献   

20.
Thermal properties, water durability and structure of Nb2O5–SrO–P2O5 glasses containing 0–25 mol% Nb2O5 and 35–60 mol% SrO were explored aiming to develop high refractive index optical glasses. Structure studied using Raman and NMR spectra reveals that by increasing Nb2O5 content, niobium plays the role as intermediate. Nb5+ tends to break P–O–P and O–P–O bonds forming [NbO6] structure. Thus fractions of Q3 and Q2 decrease, while Q1 fraction increases. Furthermore the Q0 fraction replaces the lessened Q3 fraction. As P2O5 content is reduced to 30 mol%, partial [NbO6]octa turns into [NbO4]tetra and partial (Nb–O)short-octa becomes (Nb–O)short-tetra bond to stabilize the glass structure. Glass-transition and softening-temperatures of the glasses increase by increasing SrO and Nb2O5 contents. Thermal expansion coefficient increases by increasing SrO while decreases with Nb2O5 content. Water durability is enhanced as increasing Nb2O5 and SrO contents. Properties of the glasses correlate well with the worked out structure.  相似文献   

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