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1.
In Ge–As–Te system, the glass forming region determined by normal melt quenching method has two regions (GFR I and GFR II) separated by few compositions gap. With a simple laboratory built twin roller apparatus, we have succeeded in preparing Ge7.5AsxTe92.5−x glasses over extended composition ranges. A distinct change in Tg is observed at x = 40, exactly at which the separation of the glass forming regions occur indicating the changes in the connectivity and the rigidity of the structural network. The maximum observed in glass transition (Tg) at x = 55 corresponding to the average coordination number (Zav) = 2.70 is an evidence for the shift of the rigidity percolation threshold (RPT) from Zav = 2.40 as predicted by the recent theories. The glass forming tendency (Kgl) and ΔT (=Tc−Tg) is low for the glasses in the GFR I and high for the glasses in the GFR II. 相似文献
2.
J. Zavadil P. Kostka J. Pedlikova K. Zdansky M. Kubliha V. Labas J. Kaluzny 《Journal of Non》2009,355(37-42):2083-2087
Chalcogenide bulk glasses Ge20Se80−xTex for x(0,15) have been prepared by systematic replacement of Se by Te. Selected glasses have been doped with Ho, Er and Pr, and samples have been characterized by transmission spectroscopy, measurements of dc electrical conductivity and low-temperature photoluminescence. Absorption coefficients have been derived from measured transmittance and estimated reflectance. Arrhenius plots of dc electrical conductivity, in the measured temperature range 300–460 K, are characterized by single activation energies roughly equal to the half of the optical gap. Activation energies deduced from Arrhenius plots reveal a systematic decrease with increasing Te content. Similarly, both absorption and low-temperature photoluminescence spectra reveal shifts of absorption edge and/or dominant luminescence band to longer wavelength due to Te → Se substitution. Samples doped with Ho and Er exhibit a strong luminescence at 1200 and 1540 nm due to 5I6 → 5I8 and 4I13/2 → 4I15/2 transitions of Ho3+ and Er3+ ions, respectively. Pr doped samples exhibit only a relatively weak luminescence peak at 1590 nm, which we tentatively assign to 3F3 → 3H4 transition of Pr3+ ions. Absorption of the base glass luminescence at 1460 and 1520 nm has been observed at low temperature on samples doped with Pr and Er, respectively. 相似文献
3.
F. Kyriazis A. Chrissanthopoulos V. Dracopoulos M. Krbal T. Wagner M. Frumar S.N. Yannopoulos 《Journal of Non》2009,355(37-42):2010-2014
We report on the structural details and microphase separation of the bulk glasses Agx·(As33S67)100-x for 0x25. Glass–glass phase separation occurs over a wide range of Ag content, i.e. 4x20. An off-resonant polarized Raman spectroscopic study has been carried out to elucidate structural aspects at the short- and medium-range structural order of the glasses. Analysis of Raman spectra revealed quantitative changes of the sulfur-rich microenvironments that reduce upon adding Ag. Scanning electron microscopy combined with X-rays microanalysis have been utilized to examine the type and extent of phase separation, and to provide quantitative details on the atomic concentrations in the Ag-poor and Ag-rich phases. It has been shown that at 7 at.% Ag the Ag-rich phase percolates through the structure; this effect can be associated with an ionic-to-superionic behavior of these glasses in accordance with similar studies on the stoichiometric arsenic sulfide glass; although the phase separation observed in the present glasses is qualitatively different. 相似文献
4.
S. Maurugeon B. Bureau C. Boussard-Pldel A.J. Faber X.H. Zhang W. Geliesen J. Lucas 《Journal of Non》2009,355(37-42):2074-2078
Te80−xGe20Sex glasses have been prepared along the GeSe4–GeTe4 axis using the classical method in silica tube under vacuum. A phase separation domain appears for composition around Te40Ge20Se40. Our attention was turned toward the Te-rich compositions corresponding to 1 < x < 5 at.%. These glasses are transparent from 4 to about 20 μm without any purification of the starting elements. Furthermore the difference ΔT between the crystallization temperature Tx and the vitreous transition temperature Tg lies at about 110 °C that is to say 30 °C higher than for the GeTe4 reference glass. Finally the introduction of a few percentages of Se makes the glasses much easier to prepare and more stable against crystallization, making them drawable as optical fibers for example. Taking into account their transparency window, encompassing the CO2 absorption band around 15 μm, the Te80−xGe20Sex with 1 < x < 5 at.% could become matchless composition for the CO2 infrared detection as planed by the Darwin mission of the European Space Agency. 相似文献
5.
Thermal properties and structure of AsxSe100−x and SbxSe100−x glass-forming systems (x = 0, 1, 2, 4, 8 and 16) were studied by conventional and StepScan DSCs and Raman spectroscopy. Compositional dependence of the glass transition temperature, Tg, was determined from reversible part of StepScan DSC records and discussed. The attention was also focused on the crystallization of undercooled melts of these systems. It was found that only selenium crystallizes from undercooled melts of As–Se system and its tendency to crystallize decreases markedly with increasing As content, for arsenic content higher than 4 at.% no crystallization was observed. In the case of Sb–Se system Sb2Se3 crystallizes in the first step followed by trigonal selenium crystallization from non-stoichiometric undercooled melt. Sb2Se3 crystallizes from incongruent melt with crystallization enthalpy ΔHc(Sb2Se3) = −52 ± 2 J/(g of Sb2Se3), Johnson–Mehl–Avrami kinetics of crystallization and kinetic exponent close to 3 was found. Raman spectra were measured to obtain basic information on the structure of both glassy systems. 相似文献
6.
We have employed Dy L3-edge extended X-ray absorption fine structure measurements to investigate the local structures of Dy doped in Ge–As–S and Ge–Ga–S glasses. It turned out that Dy–S distance on average is conspicuously longer in Ge–Ga–S glass despite the number of the nearest neighboring S atoms being nearly identical with each other. The enhanced rare-earth solubility of Ge–Ga–S glass is then explained in connection with decrease in covalence of Ga–S bonds compared with Ge–S or As–S bonds, and structural correlation between GaS4 tetrahedra and Dy. The discrepancy in the local structural environments of trivalent Dy, however, results in no significant changes in the spectral lineshape and the mean energy of its intra-4f-configurational transitions. 相似文献
7.
J. Orava T. Kohoutek T. Wagner Z. Cerna Mil. Vlcek L. Benes B. Frumarova M. Frumar 《Journal of Non》2009,355(37-42):1951-1954
The optical and structural properties of Ge20Se80, Ge25Se75 and Ge30Se70 bulk glasses and Agx(Ge0.20Se0.80)100−x thin films, where x = 0, 6, 11, 16, 20 and 23 at.% were studied. All samples were confirmed as amorphous according to XRD. The Raman spectra showed increase in 260 cm−1 and 237 cm−1 and decrease in 198 cm−1 and 216 cm−1 bands with different Se content in the bulk samples. The optical bandgap energy of bulk samples decreased (2.17–2.08 eV) and refractive index increased (2.389–2.426 at 1550 nm) with increasing Se content in bulk glasses. The Ge20Se80 thin films were prepared by vacuum thermal evaporation from Ge30Se70 bulk glasses. The Raman spectra of the films showed that peaks at 260 cm−1 and 216 cm−1 decreased their intensities with increasing Ag content in the thin films. The significant red shift of bandgap energy occurred upon different Ag content. The optically induced dissolution and diffusion resulted in graded refractive index profile along the film thickness caused by different Ag concentration. The refractive index increased from the substrate side to the top of thin films. The graded profile was getting more uniform with increasing content of silver in the thin film. 相似文献
8.
The interest in superionic systems has increased in recent years because of the potential application of these materials as solid electrolytes. In this field, amorphous materials present important advantages when compared to the crystalline solids: larger conductivity, isotropy and absence of grain boundaries. In this work, amorphous alloys of compositions (Ge25Se75)100−yAgy with y=10, 15, 20 and 25 at.% have been studied. Amorphous samples in bulk were obtained from the liquid by water quenching (melt-quenching technique). The crystallization kinetics of the amorphous alloys have been studied under continuous heating and isothermal conditions by means of differential scanning calorimetry. A glass transition and two exothermic transformations were observed in all the samples. The quenched samples and the crystallization products have been characterized by X-ray diffraction. The primary crystallization of the ternary phase Ag8GeSe6 and the secondary phase GeSe2 was observed. The glass and crystallization temperatures, the activation energy and the crystallization enthalpy are reported. The first step of the crystallization of the Ag8GeSe6 phase in all the (Ge25Se75)100−yAgy samples is modelled taking into account the Johnson–Mehl–Avrami–Kolmogorov theory and considering that the changes in the composition only modify the viscosity of the undercooled liquid. The transformation diagrams (TTT and THRT) are calculated and the glass forming ability is analyzed. The experimental results are discussed and correlated with the structures proposed for the glass. The present results and conclusions are also compared with those reported by other authors. 相似文献
9.
The Raman spectra of Ge–S glasses in the Ge-rich region from Ge 33% to 46% have been investigated in order to know the structural development of the network glasses. From the detailed curve fits, we have found that there is an unassigned peak at 410 cm−1 and it becomes larger with increasing Ge composition. To clarify the structural origin of the peak, we virtually constructed the atomic arrangement of the glassy state starting from the crystalline state through the liquid state and changed the composition gradually depleting the medium in sulfur. From the consideration of the structural modeling and the atomic orbital theory, we suggest that single Ge–S chain is a probable structural origin of the peak. 相似文献
10.
The crystallization behavior and kinetics of glasses produced from coal fly ashes, red mud and silica fume were investigated by using differential thermal analysis, X-ray diffraction and scanning electron microscopy techniques. The kinetic parameters of the glass-crystallization transformation were estimated under non-isothermal conditions applying three different equations, namely, Kissinger, Matusuta-Sakka and Ozawa. Non-isothermal differential thermal analysis curves were obtained using both coarse and fine glass samples. The crystallization activation energies of coarse glasses are in the range of 233-439 kJ/mol while the activation energies of fine glasses change in the range of 369-450 kJ/mol. Avrami exponent, n, values of coarse glasses indicated the three-dimensional bulk crystallization. This result is in well agreement with the cross-sectional scanning electron microscopy investigations. The values of the n obtained experimentally are in the range of 1.24-1.36 for fine glasses which show the one-dimensional surface crystallization. The crystallized phase of the glass-ceramic samples produced from waste glasses by applying the controlled heat treatment process was identified as diopside by X-ray diffraction analysis. 相似文献
11.
Chalcogenide glasses (ChG) have proven to be promissory materials for their application as sensitive membranes in ion-selective electrodes (ISE’s), which are used in electrochemical sensors in order to detect heavy metal ions in solutions. AgGeSe system is not an exception. ChG system Agx(Ge0.25Se0.75)100−x with x between 10 and 25 at.% was investigated as membrane material in ion-selective electrodes. This system has shown sensitivity to the presence of Cu2+ and Fe3+ ions. The introduction of Cu or Fe to the ChG composition was made in order to explore the role of metal addition on selectivity towards Cu2+ or Fe3+ ions. The analytical properties such as reproducibility, linear range, sensitivity, detection limit and working pH range were studied and its dependence on the ChG composition was analyzed for the three systems. The cross-selectivity of some interfering ions was investigated. 相似文献
12.
The thermodynamical miscibility in 0.8[xB2O3-(1 − x)P2O5]-0.2K2O glasses has been studied by measuring the glass transition temperature and the mixing enthalpy. Measurements have been performed by differential scanning calorimeter and hydrofluoric acid solution calorimetry at 298 K. The enthalpies of mixing are significantly negative over the whole range of composition. The results are discussed in terms of intermolecular associations. 相似文献
13.
C. E. Crowder J. U. Otaigbe M. A. Barger R. L. Sammler B. C. Monahan C. J. Quinn 《Journal of Non》1997,210(2-3)
Melt crystallization of two zinc alkali phosphate glasses was studied with X-ray diffraction (XRD) experiments to accelerate efforts to melt process these glasses with organic polymers. The inorganic glasses differed markedly in chemical durability (water sensitivity) and crystallization rates. They were studied at room temperature prior to and after melt processing with XRD experiments and in situ at melt temperatures without flow in a novel differential scanning calorimeter/XRD apparatus. The glasses were found to be amorphous at room temperature and semi-crystalline above their glass-transition temperatures. Higher temperatures and shear (mixing) rates increased the crystallization rate of the glasses. The non-durable (water-sensitive) glass was observed to contain significant levels of crystalline matter after melt processing at 400°C. This process-induced crystallization of the glasses must be controlled, possibly during processing and/or glass formulation, otherwise it may lead to formation of unwanted phase-separated defects in the glass. If high levels of the crystalline matter are present during melt processing, they may lead to irreversible plugging of the processing equipment. 相似文献
14.
Erbium doped chalcogenide glasses are of great interest in the integrated optoelectronic technology due to their Er3+ intra-4f emission at the standard telecommunication wavelength of 1.54 μm. In this paper, the photoluminescence (PL) of a series of (GeS2)x(Ga2S3)100−x (x = 75 and 67) glasses doped with high amounts of Er2S3 (1.8, 2.1, 2.4 and 2.7 mol%) under excitation with 1064 nm light has been studied. A quenching PL effect at 1.22 аt.% Er-doped (GeS2)75(Ga2S3)25 and 1.39 аt.% Er-doped (GeS2)67(Ga2S3)33 glasses has been established. The relative changes in PL line-shape at around 1540 nm have been estimated by deconvoluting the spectra to Gaussian sub-bands centered at 1519 ± 1, 1537 ± 1, 1546 ± 1, 1555 ± 1 and 1566 ± 4 nm, which correspond to F21, F11, F22, F12 and F13 transitions in the 4I13/2 and 4I15/2 energy levels and have intensity and manifestation that are strongly depend on the Er-doping level. The influence of gallium on the PL efficiency has been evaluated with a view to enhanced emission cross-section. 相似文献
15.
L. M. Dolginov P. G. Eliseev A. N. Lapshin M. G. Milvidskii 《Crystal Research and Technology》1978,13(6):631-638
The phase diagram of the Ga–In–As–Sb quaternary system has been determined experimentally and also has been treated on the base of thermodynamic calculations. The liquidus data were obtained by DTA and solidus data were determined using electron microprobe analysis on LPE-layers of GaxIn1–xAsySb1–y on GaSb and InAs substrates. Isolattice-parameter heterostructures prepared on these substrates were free of mismatch dislocations and suitable for application to light-emitting diodes and semiconductor lasers. 相似文献
16.
Metallic glasses based on Au of composition Au49Cu26.9Ag5.5Pd2.3Si16.3 and (Au49Cu26.9Ag5.5Pd2.3Si16.3)99X1 where X = Ti and In, have been produced and characterized in ribbon form. They show a glass transition and a rather wide undercooled liquid region before crystallisation.The fragility index (m) of the alloys was investigated with two methods involving differential scanning calorimetry (DSC) measurements. In one method the glass transition temperature was determined at different scanning rates in the range 0.3-100 °C/min and its trend fitted to give m. In the other m was obtained from the temperature span of the glass transition range at the scanning rate of 20 °C/min. Implications for viscosity in the undercooled liquid are derived and thoroughly discussed ending with a VFT (Vogel-Fulcher-Tammann) expression for it. 相似文献
17.
The structure of SbxSe100−x bulk glasses is investigated with the aid of Raman scattering over a wide composition range. The Raman spectra of the glasses exhibit unusual features when compared with other structurally similar binary glasses, owing to the phase separation of the present glasses in a certain composition range. The evolution of the Raman spectra and the depolarization ratio of the polarized and depolarized Raman intensities are consistent with the phase separation effect. The present findings are discussed alongside with calorimetric data from the literature that have been used up to now to extract structural information in an indirect way. The capability of Raman scattering as a tool for investigating phase separation in homogeneous media is demonstrated. 相似文献
18.
The transition from the crystalline state to amorphous state and back has been studied in the particular case of the GeSb2Te4 phase-change material by a computer simulation procedure. Modelling at the nanoscale indicates specific structural characteristics, especially the multiplicity of the amorphous phase as opposite to the uniqueness of the crystalline phase. In the particular case of the Si12Ge10As30Te48 switching glass two types of ordering have been pointed out and characterized. 相似文献
19.
Equilibria between quaternary liquid phases Ga–In–As–Ge(–Sn) and the ternary solid phase Ga–In–As have been calculated by application of the KRUPKOWSKI formalism on the excess free enthalpy. Experimental liquidus data were obtained from solubility experiments in a LPE equipment. Results of calculation and experimental liquidus data are compared. 相似文献
20.
ZBLAN glasses with the composition (in mol%) of (100 − x)(53 ZrF4 + 19 BaF2 + 5LaF3 + 3AlF3 + 20NaF) + xTiO2 (x = 0, 1.0 and 2.0 mol%) were prepared using a conventional melting technique in dry nitrogen atmosphere. The thermal stability, glass-forming ability, and crystallization kinetics of the ZBLAN system as a function of the TiO2 concentrations were investigated by Differential Scanning Calorimetry (DSC). Also, the crystalline phases were determined by X-ray Diffraction (XRD). Our study indicates that adding TiO2 in a fluoride system improves the thermal parameters of the glass, which is interesting for applications as optical fiber. 相似文献