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1.
Precursor glass of composition 25K 2O–25Nb 2O 5–50SiO 2 (mol%) doped with Er 2O 3 (0.5 wt% in excess) was isothermally crystallized at 800 °C for 0–100 h to obtain transparent KNbO 3 nanostructured glass–ceramics. XRD, FESEM, TEM, FTIRRS, dielectric constant, refractive index, absorption and fluorescence measurements were carried out to analyze the morphology, dielectric, structure and optical properties of the glass–ceramics. The crystallite size of KNbO 3 estimated from XRD and TEM is found to vary in the range 7–23 nm. A steep rise in the dielectric constant of glass–ceramics with heat-treatment time reveals the formation of ferroelectric nanocrystalline KNbO 3 phase. The measured visible photoluminescence spectra have exhibited green emission transitions of 2H 11/2, 4S 3/2 → 4I 15/2 upon excitation at 377 nm ( 4I 15/2 → 4G 11/2) absorption band of Er 3+ ions. The near infrared (NIR) emission transition 4I 13/2 → 4I 15/2 is detected around 1550 nm on excitation at 980 nm ( 4I 15/2 → 4I 11/2) of absorption bands of Er 3+ ions. It is observed that photoluminescent intensity at 526 nm ( 2H 11/2 → 4I 15/2), 550 nm ( 4S 3/2 → 4I 15/2) and 1550 nm ( 4I 13/2 → 4I 15/2) initially decrease and then gradually increase with increase in heat-treatment time. The measured lifetime ( τf) of the 4I 13/2 → 4I 15/2 transition also possesses a similar trend. The measured absorption and fluorescence spectra reveal that the Er 3+ ions gradually enter into the KNbO 3 nanocrystals. 相似文献
2.
Nd 3+-doped precursor glass in the K 2O–SiO 2–Y 2O 3–Al 2O 3 (KSYA) system was prepared by the melt-quench technique. The transparent Y 3Al 5O 12 (YAG) glass–ceramics were derived from this glass by a controlled crystallization process at 750 °C for 5–100 h. The formation of YAG crystal phase, size and morphology with progress of heat-treatment was examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Fourier transformed infrared reflectance spectroscopy (FT-IRRS). The crystallite sizes obtained from XRD are found to increase with heat-treatment time and vary in the range 25–40 nm. The measured photoluminescence spectra have exhibited emission transitions of 4F 3/2 → 4I J ( J = 9/2, 11/2 and 13/2) from Nd 3+ ions upon excitation at 829 nm. It is observed that the photoluminescence intensity and excited state lifetime of Nd 3+ ions decrease with increase in heat-treatment time. The present study indicates that the incorporation of Nd 3+ ions into YAG crystal lattice enhance the fluorescence performance of the glass–ceramic nanocomposites. 相似文献
3.
Glasses in the system Li 2O–SnO–B 2O 3 system were prepared by a melt-quenching method. Thermal and viscous properties and local structure of these glasses were investigated. The SnO–B 2O 3 glasses exhibited relatively low glass-transition temperatures ( Tg) around 350 °C and excellent thermal stability against crystallization. Viscosity measurements in the vicinity of Tg indicated that the glasses were considerably fragile compared to alkali borate glasses. Fraction of four-coordinated boron was maximized at the composition with 50 mol% SnO and that of nonbridging oxygen, which is not purely ionic in alkali borate systems but partially covalent, augmented with an increase in the SnO content. Correlation between glass properties and structure was discussed in the SnO–B 2O 3 binary system. 相似文献
4.
In the present study, results concerning luminescence and dielectric properties of Eu 2O 3 (0.5 wt% in excess) doped nano-crystallized KNbO 3 containing transparent glass-ceramics obtained from glass of composition 25K 2O–25Nb 2O 5–50SiO 2 (mol%) by varied heat-treatment duration at 800 °C have been analyzed and reported. The formed crystallization phase, crystallite size and morphology have been examined through XRD, FESEM, TEM and FTIRRS measurements. The observed steep increase in the dielectric constant ( ?) of glass-ceramics over the as-prepared glass is attributed to the formation of ferroelectric nano-crystalline KNbO 3 in glass matrix. The absorption spectra of all the samples have revealed the characteristic 4f–4f intraband absorption transitions of Eu 3+ ions. The measured photoluminescence spectra have exhibited emission transitions 5D 0, 1 → 7F j ( j = 0, 1, 2, 3 and 4) of Eu 3+ ions. The excited level lifetimes have been determined from measured fluorescence decay curves. The rare earth ion site symmetry (nearly Cv) has been understood based on the nature of the Stark splittings of emission bands detected in both Eu 3+: glass and Eu 3+: glass-ceramics. 相似文献
5.
The effect of the SrO addition on the microstructure and structure of the glazes from the SiO2–Al2O3–CaO–MgO–K2O system was investigated in this study. The results were obtained by testing the ability of the frits crystallization, the stability of the crystallizing phases during the single-step fast-firing cycle depending on their chemical composition and the effect of addition of strontium oxide. Differential scanning calorimetry (DSC) curves showed that all glazes crystallized, and diopside and anorthite were mainly identified as dominant phases in the obtained glazes, while the size and amount of each depended on the amount of SrO introduced. The thermal characteristic of the frits was carried out using DSC, and crystalline phases were determined by X-ray diffractometry. The glaze microstructure was investigated by scanning electron microscopy and transmission electron microscopy. Additional information on the microstructure of frits was derived from spectroscopic studies in the mid-infrared range. 相似文献
6.
The partial system ErPO 4–NaPO 3–Er(PO 3) 3 of the Er 2O 3–Na 2O–P 2O 5 oxide system has been investigated by thermoanalytical methods and X-ray powder diffraction. On the basis of the obtained results the phase diagram of the partial system is proposed. The system is bounded by three subsystems: (i) ErPO 4–Er(PO 3) 3, (ii) Er(PO 3) 3–NaPO 3 and (iii) ErPO 4–NaPO 3. Their phase diagrams are proposed. In the Er(PO 3) 3–NaPO 3 subsystem an intermediate compound NaEr(PO 3) 4 occurs; it melts incongruently at 655 °C. It was found that ErPO 4 and NaEr(PO 3) 4 form a section which is a real system only in the subsolidus region (below 646 °C). Two ternary invariant points (one ternary peritectic and one ternary eutectic) occur in the investigated partial system ErPO 4–NaPO 3–Er(PO 3) 3. 相似文献
7.
Phase equilibria up to solidus line in CuO?CIn 2O 3 system have been investigated using XRD and DTA/TG methods. According to the results, only one compound of the formula Cu 2In 2O 5 formed in the system studied. Its thermal stability was determined in the air and argon proving that the compound did not melt but underwent decomposition. The decomposition of Cu 2In 2O 5 in the air atmosphere began at 1080?°C, while in argon at 835?°C. Additional studies were undertaken to determine the hitherto unknown colour properties of samples representing the CuO?CIn 2O 3 system in the equilibrium state. 相似文献
8.
Glass–ceramic in the MgO–Al 2O 3–SiO 2 system with crystallization ability of gahnite (ZnO·Al 2O 3) and mullite were synthesized. It was found that the glass–ceramic containing gahnite phase had desirable mechanical behavior and reached to an acceptable hardness and density. The compositions were designed based on magnesium oxide replacement (from MgO–Al 2O 3–SiO 2 glass–ceramic system) with zinc oxide. Glass–ceramics were characterized by DTA, X-ray diffraction and scanning electron microscopy. Heat treatment at 1100 °C cause form gahnite crystals in glass–ceramic. Microhardness increased with increasing gahnite crystals. To achieve good mechanical properties, the initially formed high gahnite phase must transform. 相似文献
9.
Research on Chemical Intermediates - CuAl2O4–Al2O3–SiO2 nanocomposites with different amounts of CuAl2O4 (40, 50, 60 and 70 wt. %) were synthesized by the sol–gel method and... 相似文献
10.
The water activity and osmotic coefficients of the system { y NH 4NO 3+(1- y) KNO 3}(aq) has been measured at total molalities from 0.2 mol kg −1 to about saturation of one of the solutes for different ionic-strength fractions y of NH 4NO 3 with y=0.2, 0.5 and 0.8 at the temperature 298.15 K using the hygrometric method. The obtained data allow the deduction of the thermodynamic parameters. From these measurements, new Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results obtained are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions of NH 4NO 3. 相似文献
12.
The Na 2O–CaO–SiO 2 ternary glass–ceramic with the composition of 49 mass% Na 2O, 20 mass% CaO, and 31 mass% SiO 2 was prepared by the conventional method. The ternary glass–ceramic was characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Fourier transform infrared spectroscopy, and scanning electron microscopy techniques. The Na 2CaSiO 4 phase, having the cubic crystal system, with the crystallite size of 25.14 nm and lattice parameter of 0.7506 nm was determined from the XRD pattern. The activation energy of the glass–ceramic calculated from the DTA curves was found to be 162.02 kJ mol ?1. The Avrami exponent was found to be ~2 indicating a one-dimensional growth process. The mass loss percent from ambient temperature to 1,173 K is less than 1 %. The density was calculated to be 2,723 kg m ?3. The fine-grained microstructure with the particle sizes less than 1 μm was confirmed by the scanning electron microscope micrograph. 相似文献
13.
A phase equilibria diagram of the partial system NdPO 4–K 3PO 4–KPO 3 has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd 2O 3–K 2O–P 2O 5. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K 3Nd(PO 4) 2–K 4P 2O 7, NdPO 4–K 5P 3O 10 and NdPO 4–K 4P 2O 7 have been identified in the partial NdPO 4–K 3PO 4–KPO 3 system. Previously unknown potassium-neodymium phosphate “K 4Nd 2P 4O 15” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO 4 and K 4P 2O 7. Four invariant points: two quasi-ternary eutectics, E 1 (1057 °C) and E 2 (580 °C) and two quasi-ternary peritectics, P 1 (1078 °C) and P 2 (610 °C), occur in the NdPO 4–K 3PO 4–KPO 3 region. 相似文献
14.
Li 2O–MoO 3–B 2O 3 glasses mixed with different concentrations of CuO (ranging from 0 to 1.2 mol%) were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Optical absorption, luminescence, ESR, IR and dielectric properties (viz., dielectric constant ?′, loss tan δ and a.c. conductivity σac, over a wide range of frequency and temperature) of these glass materials have been investigated. The results of differential scanning calorimetric studies suggest that the glass forming ability is higher for the glasses containing CuO beyond 0.6 mol%. The analysis of results of the dielectric properties has revealed that the glasses possess high insulating strength when the concentration of CuO is >0.6 mol%. The variation of a.c. conductivity with the concentration of CuO passes through a maximum at 0.6 mol%. In the high-temperature region, the a.c. conduction seems to be connected with the mixed conduction viz., electronic conduction and ionic conduction. The optical absorption spectra of these glasses exhibited bands due to Cu + ions in the UV region in addition to the conventional band due to Cu 2+ ions in the visible region. The ESR spectral studies have indicated that there is a gradual adoption of Cu 2+ ions from ionic environment to covalent environment as the concentration of CuO increases beyond 0.6 mol% in the glass matrix. The luminescence spectra excited at 271 nm have exhibited an intense yellow emission band centered at about 550 nm and a relatively broad blue emission band at about 450 nm; these bands have been attributed to the 3D 1 → 1S 0 transition of isolated Cu + ions and 3D 1 → 1S 0 transition of (Cu +) 2 pairs, respectively. The quantitative analysis of the results of all these studies has indicated that as the concentration of CuO is increased beyond 0.6 mol% in the glass matrix, a part of Cu 2+ ions have been reduced to Cu + ions that have influenced the physical properties of these glasses to a substantial extent. 相似文献
16.
Diamond composites were prepared by sintering diamond grains with low melting Na 2O–B 2O 3–SiO 2 vitrified bonds in air. The influence of ZnO on the wettability and flowing ability of Na 2O–B 2O 3–SiO 2 vitrified bonds was characterized by wetting angle, the interfacial bonding states between diamond grains and the vitrified bonds were observed by scanning electron microscope (SEM), and the micro-scale bonding mechanism in the interfaces was investigated by means of energy-dispersive spectrometer (EDS), Fourier transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS). The experimental results showed that ZnO facilitated the dissociation of boron/silicon–oxygen polyhedra and the formation of larger amount of non-bridging oxygen in the glass network, which resulted in the increase of the vitrified bonds' wettability and the formation of –CO, –O–H and –C–H bonds on the surface of diamond grains. B and Si diffused from the vitrified bonds to the interface, and C–C, C–O, CO and C–B bond formed on the surface of sintered diamond grains during sintering process, by which the interfacial bonding between diamond grains and the vitrified bonds was strengthened. 相似文献
17.
Multicomponent glasses from the SiO 2–P 2O 5–K 2O–MgO–CaO–CuO system acting as slow release fertilizers were synthesized by the melt-quenching technique. The influence of CuO and P 2O 5 addition on the structure of glasses was evaluated by FTIR, Raman, 31P, and 29Si MAS NMR spectroscopies. The studies showed that the Cu 2+ ions displacing Ca 2+ ions and Mg 2+ ions in the structure of glass prefer to associate with the phosphorus Q 1 species, forming the Q 0 species with chemically stable POCu bonds. This is accompanied by the reduction of the degree of polymerization of the phospho-oxygen sub-network, with a simultaneous increased degree of polymerization of the silico-oxygen sub-network of the silicate–phosphate glasses. 相似文献
18.
A novel and simple approach is reported to fabricate uniform single-crystal ZnO nanorods in ionic liq-uids. The as-obtained ZnO nanorods have been characterized by XRD,TEM,HRTEM,SAED,XPS,EDXA,PL and UV-vis absorption spectra. The rod diameters of the nanostructures can be controlled by tuning the amount of sodium hydroxide in the synthesis. Photoluminescence results show that the nanos-tructural ZnO exhibits better optical properties than bulk ZnO does and interestingly,the smaller the rod diameters are,the better optical property 1D nanostructural ZnO exhibits. The possible growth mechanism of ZnO nanorods is also investigated. 相似文献
19.
The mixed aqueous electrolyte system magnesium and manganese sulfate has been studied with the hygrometric method at the temperature 298.15 K. The relative humidity of this system is measured at total molalities from 0.2 mol kg −1 to about saturation of one of the solutes for different ionic-strength fractions y of MgSO 4 with y=0.2, 0.5 and 0.8. The obtained data allow the deduction of new thermodynamic parameters. The experimental results are compared with the predictions of ZSR rule. From these measurements, the new Pitzer mixing ionic parameters are determined and used to predict the solute activity coefficients in the mixture. The obtained results are used to calculate the excess Gibbs energy at total molalities for different ionic-strength fractions y of MgSO 4. 相似文献
20.
Journal of Sol-Gel Science and Technology - ZnO–B2O3–SiO2:Mn2+ (ZBSM) optical-storage glass–ceramics doped with ZnF2 were successfully prepared via sol–gel method. The... 相似文献
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