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1.
M. Çelikbilek 《Journal of Non》2011,357(1):88-95
The crystallization kinetics of the (1 − x)TeO2-xWO3 (where x = 0.10, 0.15, and 0.20, in molar ratio) glass system was studied by non-isothermal methods using differential scanning calorimetry (DSC), X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. DSC measurements were performed at different heating rates to study crystallization kinetics of the first crystallization reactions of the glasses. XRD analysis of tungsten-tellurite glasses heat-treated above the first crystallization temperatures revealed that the first crystallization peaks attributed to the α-TeO2 and γ-TeO2 crystalline phases for 0.90TeO2-0.10WO3 and 0.85TeO2-0.15WO3 samples and α-TeO2 and WO3 crystalline phases for the 0.80TeO2-0.20WO3 sample. Avrami constants, n, calculated from Ozawa equation, were found between 1.14 and 1.44. The activation energies, EA, for the first crystallization reactions were determined by using the modified Kissinger equation as 379 kJ/mol, 288.1 kJ/mol and 228.8 kJ/mol, for 0.90TeO2-0.10WO3, 0.85TeO2-0.15WO3 and 0.80TeO2-0.20WO3 glasses, respectively. 相似文献
2.
N. Manikandan 《Journal of Non》2008,354(31):3732-3734
Time dependent photocurrent measurements have been undertaken on bulk Ge15Te85−xInx (1 ? x ? 11) series of glasses. It is found that samples with x < 3 do not exhibit any photo-degradation whereas a decrease in photo-conductivity under illumination is observed in samples with x ? 3. Further, the photosensitivity of Ge15Te85−xInx glasses is found to reveal specific signatures at compositions x = 3 and 7. The observed composition dependent photo-degradation behavior and photo-response of these glasses have been understood on the basis of an extended rigidity percolation and its influence on network related properties. 相似文献
3.
Two series (A and B series) of oxynitride glasses were prepared by melting batches at 1580 °C for 3 h under local CO reducing atmosphere in a Si-Mo-heated resistance furnace. Nominal compositions of A and B series glasses in equivalent percent (eq.%) are (28−x)Y:xMg:48Si:24Al:83O:17N and (28−x)Y:xMg:56Si:16Al:83O:17N (x = 0, 7, 14, 21), respectively. The influences of Mg/Y and Al/Si ratios on the properties such as glass transition temperature (Tg), crystallization temperature (TC), knoop hardness (H), three-point bending strength (σ) and chemical durability in 20%HF were investigated. At the same time, the relationship between these properties and the structures of the glasses were discussed. At constant ratio Si-Al-O-N, Tg decreases nonlinearly but glass leaching ratio increases linearly with increasing Mg/Y ratio. However, H and σ increase first and then decrease as the Mg/Y ratio increases. When the Y/Mg/O/N ratio is constant, Tg decreases slightly but H and σ increase slightly as the Al/Si ratio increases. 相似文献
4.
The glass formation region in the ternary ZnO―Bi2O3―WO3 system is determined by melt quenching technique (cooling rates 101-102 K/s). New original glasses are obtained in a narrow concentration range with high WO3 content (60-75 mol%). Homogeneous glasses of the composition (100 − x)[0.2ZnO·0.3Bi2O3·0.5WO3]xMoO3, were obtained between 20 and 60 mol% MoO3. Characterization of the amorphous samples was made by x-ray diffraction (XRD), differential thermal analysis (DTA) and infrared spectroscopy (IR). The thermal stability of glasses decreases with the increasing of MoO3 content. The glass transition temperature, Tg, varies between 340-480 °C, while the crystallization temperature, Tx, varies between 388-531 °C. The tungstate glasses possess higher crystallization temperature (Tx over 500 °C) in comparison with the other vanadate and molybdate non-traditional glasses. The glass network is realized by transformation of three-dimensional structure of WO3 into a layered one, consisting mainly of WO6 units. We supposed that the network of quaternary glasses is built up by MoO4, MoO6 and WO6. At low concentration ZnO and Bi2O3 facilitate the disorder in the supercooled melts, while at high concentration stimulate crystallization processes. These oxides belong to the intermediate ones. 相似文献
5.
Temperature-assisted electrical poling of TeO2-Bi2O3-ZnO glasses for non-linear optical applications
The suitability for effective thermal poling of the ternary tellurite glasses with the compositions (100 − 2x)TeO2-xBi2O3-xZnO (x = 5, 10 and 15, in molar percentage) for the second harmonic generation (SHG) was analyzed. The glass transitions and crystallization temperatures were studied via differential thermal analysis. The structural properties of the annealed glasses and furtherly heat-treated samples were probed by extended X-ray absorption fine structure (EXAFS) spectroscopy. Thermal poling of the glasses was undertaken conventionally at various temperatures close to the glass transition temperature under high vacuum and the second harmonic generated signals were compared. A new technique of two stage poling was tested for comparison. The non-linear second harmonic signal of the poled glasses was analyzed using the Maker-fringe technique and it was found that the two stage poling enhanced the non-linear efficiency when compared to the conventionally poled samples. 相似文献
6.
The crystallization behavior of melt-spun (Zr65Al7.5Cu27.5)100−xTix (x = 0-15; in at.%) metallic glasses has been investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). The DSC traces showed an altered crystallization mode in the vicinity of 3 at.% Ti addition. A metastable icosahedral quasicrystal precipitated at the first crystallization stage of the Ti-bearing metallic glasses, which subsequently transformed to the stable Zr2Cu-type phase in the followed exothermic reaction. The glass-forming abilities (GFAs) of these metallic glasses were assessed by the recognized GFA indicators Trg, ΔTx and γ. BMGs were easily made in the compositions containing 3-7 at.% Ti by means of copper mold casting. The validity of these parameters was clarified using the critical BMG forming diameter evidence. 相似文献
7.
Alternating differential scanning calorimetric (ADSC) studies and electrical switching experiments have been undertaken on Al15Te85−xSix (2 ? x ? 12) system of glasses. These glasses are found to exhibit two crystallization reactions (Tc1 and Tc2), for compositions with x < 8. Above x = 8, a single-stage crystallization is seen. Further, a trough is seen in the composition dependence of non-reversing enthalpy (ΔHNR), based on which it is proposed that there is a thermally reversing window in Al15Te85−xSix glasses, in the composition range 4 ? x ? 8. Electrical switching studies indicate that Al15Te85−xSix glasses exhibit a threshold type electrical switching at ON state currents less than 2 mA. Further, the switching voltages are found to increase with the increase in silicon content. It is interesting to note that the start (x = 4) and the end (x = 8) of the thermally reversing window are exemplified by a kink and a saturation in the composition dependence of switching voltages, respectively. 相似文献
8.
Pulok Pattanayak 《Journal of Non》2008,354(32):3824-3827
The composition dependence of different thermal parameters such as glass transition temperature, non-reversing enthalpy, thermal diffusivity etc., of bulk As45Te55−xIx chalcohalide glasses (3 ? x ? 10), has been evaluated using the temperature modulated Alternating Differential Scanning Calorimetry (ADSC) and Photo Thermal Deflection (PTD) studies. It is found that there is not much variation in the glass transition temperature of As45Te55−xIx glasses, even though there is a wide variation in the average coordination number . This observation has been understood on the basis that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than . Further, it is found that both the non-reversing enthalpy (ΔHnr) and the thermal diffusivity (α) exhibit a sharp minimum at a composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range 5 ? x ? 7. The results obtained clearly indicate a sharp thermally reversing window in As45Te55−xIx chalcohalide glasses around the composition x = 6. 相似文献
9.
The glasses with the compositions of 21.25RE2O3-63.75MoO3-15B2O3 (RE: Sm, Gd, Dy) were prepared and the formation of β′-RE2(MoO4)3 ferroelectrics was confirmed in the crystallized glasses obtained through a conventional crystallization in an electric furnace. The features of the glass structure and crystallization behavior were clarified from measurements of Raman scattering spectra. Continuous-wave Nd:YAG laser with a wavelength of 1064 nm (laser power: 0.6-0.9 W, laser scanning speed: S = 1-16 μm/s) was irradiated to 10.625Sm2O3-10.625Gd2O3 (or Dy2O3)-63.75MoO3-15B2O3 glasses, and the structural modification was induced at the glass surface. At the scanning speed of S = 10 μm/s, crystal lines consisting of β′-Gd2−xSmx(MoO4)3 or β′-Dy2−xSmx(MoO4)3 crystals were patterned on the glass surface. It was found that those crystal lines have the surface morphology with periodic bumps. At S = 1 μm/s, it was found that crystal lines consist of the mixture of paraelectric α-Gd2−xSmx(MoO4)3 and ferroelectric β′-Gd2−xSmx(MoO4)3 crystals, indicating the phase transformation from the β′ phase to the α phase during laser irradiation. Homogeneous crystal lines with β′-RE2(MoO4)3 ferroelectrics have not been written in this study, but further research is continuing. 相似文献
10.
N. Manikandan 《Journal of Non》2009,355(1):58-60
The thermal diffusivity (α) of As20Te80−xGax glasses (7.5 ? x ? 18.5) has been measured using photo-thermal deflection (PTD) technique. It is found that the thermal diffusivity is comparatively lower for As20Te80−xGax glasses, which is consistent with the memory type of electrical switching exhibited by these samples. Further, the thermal diffusivity of As20Te80−xGax glasses is found to increase with the incorporation of gallium initially (for x ? 9), which is consistent with the metallicity of the additive. This increase in α results in a maximum at the composition x = 9; beyond x = 9, a decrease is seen in α leading to a minimum at the composition x = 15. The observed composition dependence of thermal diffusivity of As20Te80−xGax glasses has been found to be similar to that of Al20AsxTe100−x glasses, based on which it is proposed that As20Te80−xGax glasses exhibit an extended stiffness transition with compositions x = 9 and x = 15 being its onset and completion, respectively. Also, the composition x = 17.5 at which a second maximum is seen in the thermal diffusivity has been identified to be the chemical threshold (CT) of the As20Te80−xGax glassy system, as at CT, the glass is configurationally closest to the crystalline state and the scattering of the diffusing thermal waves is minimal for the chemically ordered phase. 相似文献
11.
Refractory bulk metallic glasses and bulk metallic glass composites are formed in quaternary Ni-Nb-Ta-Sn alloy system. Alloys of composition Ni60(Nb100−xTax)34Sn6 (x = 20, 40, 60, 80) alloys were prepared by injection-casting the molten alloys into copper molds. Glassy alloys are formed in the thickness of half mm strips. With thicker strips (e.g., 1 mm), Nb2O5 and Ni3Sn phases and the amorphous phase form an in situ composite. Glass transition temperatures, crystallization temperatures, and ΔTx, defined as Tx1 − Tg (Tx1: first crystallization temperature, Tg: glass transition temperature) of the alloys increase dramatically with increasing Ta contents. These refractory bulk amorphous alloys exhibit high Young’s modulus (155-170 GPa), shear modulus (56-63 GPa), and estimated yield strength (3-3.6 GPa). 相似文献
12.
Hongxia Lu 《Journal of Non》2007,353(26):2528-2544
Tracer diffusion coefficients of the radioactive isotope Na-22 were measured in glasses of the type (CaO·Al2O3)x(2 SiO2)1−x to study the diffusion of sodium as a function of glass composition, x, temperature and initial water content. The diffusion of Na-22 in glasses diffusion-annealed in dry air can always be well described by a single tracer diffusion coefficient, but sometimes not in samples annealed in common air. It was found that the sodium tracer diffusion coefficient decreases by about six orders of magnitude when the glass composition x changes from 0 to 0.75 at 800 °C. The temperature dependence of the diffusion of sodium seems to decrease as the silica content increases. Variations of the initial water content in some of the glasses investigated did not very significantly influence the rate of the tracer diffusion of sodium. 相似文献
13.
S.B. Bhanu Prashanth 《Journal of Non》2009,355(3):164-1206
The thermal properties and electrical-switching behavior of semiconducting chalcogenide SbxSe55−xTe45 (2 ? x ? 9) glasses have been investigated by alternating differential scanning calorimetry and electrical-switching experiments, respectively. The addition of Sb is found to enhance the glass forming tendency and stability as revealed by the decrease in non-reversing enthalpy ΔHnr, and an increase in the glass-transition width ΔTg. Further, the glass-transition temperature of SbxSe55−xTe45 glasses, which is a measure of network connectivity, exhibits a subtle increase, suggesting a meager network growth with the addition of Sb. The crystallization temperature is also observed to increase with Sb content. The SbxSe55−xTe45 glasses (2 ? x ? 9) are found to exhibit memory type of electrical switching, which can be attributed to the polymeric nature of network and high devitrifying ability. The metallicity factor has been found to dominate over the network connectivity and rigidity in the compositional dependence of switching voltage, which shows a profound decrease with the addition of Sb. 相似文献
14.
Glasses in the La2O3−CaO−B2O3 ternary system were studied. The glass forming range as determined by the appearance of the annealed cast was found to match previously published findings. Clear glasses were formed in the composition range of 5.7−19.1 mol% La2O3 with constant B2O3 content of 71.4 mol%, and in glasses of constant La2O3:CaO ratio of 1:4 with B2O3 content in the range of 71.4-55.0 mol%. The non-linear optical crystalline phase La2Ca2B10O19 was crystallized from the clear glasses after heat treatments, as determined by powder XRD. Two types of the LaBO3 crystalline phases were detected in the partially and the fully crystallized glass compositions outside the glass forming range. Data are reported for the glass transition temperature (Tg), dilatometric softening point (Td), linear coefficient of expansion (α), onset crystallization temperature (Tx), exothermal peak temperature (TP), density (ρ) and index of refraction (nD) in the clear glasses. 相似文献
15.
Lead chloroantimonite glasses form stable binary glasses that may accommodate numerous oxides or halides as a third component. Molybdenum trioxide is a glass progenitor leading to molybdate glasses. Ternary glasses have been synthesized and studied in the Sb2O3-PbCl2-MoO3 system. Compositional limits of glass formation are reported and two series of glass samples have been prepared corresponding to the general formulas: (90 − x)Sb2O3-xPbCl2-10MoO3 and (90 − x)Sb2O3-xMoO3-10PbCl2. Glass transition temperature is close to 290 °C at high Sb2O3 content and decreases as antimony oxide is substituted by MoO3 or PbCl2. Position, width and intensity of crystallization peak suggest that devitrification rate is small in some composition ranges. The evolution of density, thermal expansion, refractive index and microhardness has been studied as a function of composition parameter x. Deviations from linearity are observed. They suggest structural changes in the case of the MoO3/Sb2O3 substitution while it appears that molar volume increases linearly versus lead content in the other series of glasses. Refractive index is close to 2.04. Optical transmission ranges from 550 nm in the visible spectrum to 5.5 μm in the infrared. It is limited by extrinsic absorption bands arising from hydroxyls and silicon impurities. Young's, bulk and shear moduli have been measured for the two series of samples. 相似文献
16.
Glasses of the system: (70−x) TeO2 + 15B2O3 + 15P2O5 + xLi2O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (Tg) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO2 by Li2O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm−1. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure. 相似文献
17.
Bulk glasses of the system Ga20SbxS80−x (x = 5 and 40) were prepared for the first time by the known melt quenching technique. Non-isothermal differential scanning calorimetric (DSC) measurements of as-quenched Ga20SbxS80−x (x = 5 and 40) chalcogenide glasses reveal that the characteristic temperatures e.g. the glass transition temperature (Tg), the temperature corresponding to the maximum crystallization rate (Tp) recorded in the temperature range 400-650 K for x = 5 and 480-660 K for x = 40 are strongly dependent on heating rate and Sb content. Upon heating, these glasses show a single glass transition temperature (Tg) and double crystallization temperatures (Tp1 and Tp2) for x = 5 which overlapped and appear as a single crystallization peak (Tp) for x = 40. The activation energies of crystallization Ec were evaluated by three different methods. The crystallization data were examined in terms of recent analysis developed for non-isothermal conditions. The crystalline phases resulting from (DSC) have been identified using X-ray diffraction. 相似文献
18.
K1−xRbxSb5S8 (x = 0.25, 0.5, 0.75) is a well-defined single-phase system that undergoes a reversible phase-change. We determined the activation energy of glass transition and crystallization, respectively, for the three compositions using the Kissinger and Ozawa-Flynn-Wall equations. The results have shown that for K0.25Rb0.75Sb5S8 the crystallization mechanism could be interpreted in terms of a single-step reaction. For the other two compositions the glass-to-crystal transformation is a process of increasing mechanistic complexity with time and it involves simultaneously several different nucleation and growth events. The slope of the lines in the Avrami plots was observed to be independent of heating rate for K0.25Rb0.75Sb5S8 and the mean value of the activation energy was found to be 262 ± 6 kJ/mol. For the other two compositions, the slope varies with the heating rate. In the K0.25Rb0.75Sb5S8 glasses, bulk nucleation with three-dimensional crystal growth appears to dominate the phase-change process. 相似文献
19.
The local structure of Ge and Ga ions in (1 − x)(Ge0.25Ga0.10S0.65)-xCsBr glasses (x = 0.00, 0.05, 0.10 and 0.12) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. CsBr formed [GaS3/2Br]− structural units in glass while Ge ions remained in GeS4/2 tetrahedra, unaffected by CsBr addition. Rare-earth ions can be surrounded by Br ions only when CsBr/Ga ratio in glass became larger than unity. 相似文献
20.
The influences of different alkali and alkali-earth oxide substitutions on the properties of lithium-iron-phosphate (LIP) glasses have been studied. Na2O, K2O, MgO, CaO and BaO were used to substitute Li2O to prepare LIP glasses with molar compositions of (20 − x)Li2O − xR2O(RO) − 30Fe2O3 − 50P2O5 (x = 2.4, 4, 5.6 and 7.2). The glass transition temperature (Tg) was determined by the differential thermal analysis technique. The density and chemical durability of the prepared glasses were measured based on the Archimedes principle and the weight losses after the glasses were boiled in water. The results show that Tg decreases with the initial substitutions, whereas the density and chemical durability increase. The diminution of the aggregation effect of Li+ ions on the glass structure due to the decrease in Li+ concentration, the larger molecule weights of the substitutes, the mixed-alkali and depressing effects as well the slower mobility of substitute ions mainly contribute to the initial changes in Tg, density and chemical durability of the LIP glasses, respectively. Further increasing the amounts of substitutes brings about increasing diminution of the aggregation effect of Li+ ions and breakage of the glass network on the one hand and increasing amounts of substitutes with larger molecule weights and ion radii on the other hand. Both aspects influence the glass properties oppositely and consequently non-monotonic variations in the properties of LIP glasses with the substitutions are observed. 相似文献