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1.
11B ( I=3/2) MAS NMR in the binary glass system xV 2O 5–B 2O 3 ( x=0.053, 0.43) and the ternary glass system xV 2O 5–B 2O 3–PbO (0.1 x1.5) has been investigated at room temperature. In the xV 2O 5–B 2O 3 glasses, one NMR line due to BO 3 unit was observed. Meanwhile in the xV 2O 5–B 2O 3–PbO, two NMR lines which arise from BO 3 and BO 4 units were detected, where the appearance of BO 4 units is produced by the presence of PbO. From the computer-simulation of the 11B NMR central transition line ( m=−1/2↔1/2), the quadrupole parameters ( e2qQ/ h and η) for BO 3 units in xV 2O 5–B 2O 3, and those for BO 3 and BO 4 units in xV 2O 5–B 2O 3–PbO were obtained as a function of x. As the V 2O 5 content increases in xV 2O 5–B 2O 3–PbO, the e2qQ/ h and η values of the BO 3− associated resonance are found to slightly decrease and increase, respectively. Meanwhile, the e2qQ/ h and η values of BO 4− associated resonance in xV 2O 5–B 2O 3–PbO are found to slightly increase and decrease, respectively. By comparing the intensities of the total transitions ( m=−3/2↔−1/2, m=−1/2↔1/2, and 1/2↔3/2) for the 11B NMR line of BO 3 and BO 4 units contained in xV 2O 5–B 2O 3–PbO with those of respective standard samples of 0.053V 2O 5–B 2O 3 and NaBH 4, the quantitative fractions of BO 3 and BO 4 in xV 2O 5–B 2O 3–PbO were obtained as a function of x. 相似文献
2.
NdAl 3(BO 3) 4 single crystals were grown by the flux method and the TSSG technique using a K 2O/3MoO 3/B 2O 3/0.5Nd 2O 3/KF flux system. Light-violet clear crystals could be obtained. The effects of fluoride on the growth of NAB crystals were investigated. As the content of KF was gradually increased, the growth form of NAB was changed from the equant to the columnar and the primary crystalline region of NAB was shrinked. At the ratio of KF/K 2O = 0.75, NAB crystals could not be grown. 相似文献
3.
The short range structures of B 2O 3 (90 mol%)---Cs 2O (10 mol%) and B 2O 3 (80 mol%)---Cs 2O (20 mol%) liquids were analyzed at 973 and 1053 K, respectively, by an X-ray diffraction method, and the effects of Cs 2O addition on the boron-oxygen bonding were investigated. The existence of BO 3 triangles, which form the so-called boroxol ring structure, was confirmed in B 2O 3---Cs 2O liquids, as well as in B 2O 3 liquid, but some fraction of the BO 3 triangles was thought to be converted to BO 4 tetrahedra. Similar results have previously been observed also in B 2O 3---Cs 2O glasses. A Cs atom was found to be surrounded by six O atoms; four Cs---O interatomic distances were about 3.2 Å but the other two were at 3.8–3.9 Å. These distances indicate that distorted Cs---O octahedra may exist in these B 2O 3---Cs 2O liquids. 相似文献
4.
Ag particles of different sizes in the nanometer range were produced in Na 2O---B 2O 3 glasses containing Ag 2O by the melt-quenching and heat-treatment method. The quenching rate was 10 3 K s −1 and the heat treatment was at 738 K for 2–300 h. The precipitation was dependent on diffusion limited growth. The optical absorption of Ag particles in the glasses was measured and correlated to the distribution of particle radii. The peak energy of the surface plasmon resonance was blue shifted and the width decreased with increasing average particle radius. These results are compared with previous data on similar systems. 相似文献
5.
The densities have been systematically measured in xLi 2O–(1− x)B 2O 3 melts of different compositions with Li 2O content varying from x=0 to 0.68 from their respective melting points up to about 1450 K with a modified Archimedean method. The density decreased with increasing temperature for all the melts measured in this work. When x<0.15, the plot of temperature versus density could be well fitted by a quadratic polynomial function, and when x0.15, density decreased linearly with increasing temperature. At a fixed temperature, the density of the melts increased rapidly with Li 2O content, went through a maximum at about x=0.333 (Li 2O–2B 2O 3), and then decreased slowly as Li 2O content was further increased. In addition, the volume expansion coefficient ( β) was calculated based on the densities measured in this work, and it was found that a maximum value appeared in the dependence of β on the molar ratio of Li 2O at about x=0.333. 相似文献
6.
A new crystal of Nd 3+:Sr 3Y(BO 3) 3 with dimension up to 25×35 mm 2 was grown by Czochralski method. Absorption and emission spectra of Nd 3+: Sr 3Y(BO 3) 3 were investigated . The absorption band at 807 nm has a FWHM of 18 nm. The absorption and emission cross sections are 2.17×10 −20 cm 2 at 807 nm and 1.88×10 −19 cm 2 at 1060 nm, respectively. The luminescence lifetime τ f is 73 μs at room temperature 相似文献
7.
Alkoxide derived gels were prepared in the system Na 2O---B 2O 3---SiO 2. The gel compositions were situated in the liquid-liquid immiscibility area of the phase equilibrium diagram. Hydrolytic resistance tests were performed on the gels heat-treated at temperatures ranging between 120 to 850 °C. The Na2O, B2O3 and SiO2 extracted from the attack gels were analyzed. The experimental results indicate that the amount of B2O3 has a significant influence on the chemical durability of the heat-treated gels. At temperatures of 850 °C the greater the B2O3 mol% the greater are the amounts of Na2O and B2O3 extracted. Different behaviour was observed for gels heat-treated at 600 °C where the amounts of B2O3 and Na2O extracted slightly increases as the B2O3 mol% increases. Small amounts of extracted SiO2 were always observed. These results are complemented with other measurements so that an explanation of the controlling mechanism is given. 相似文献
8.
Mössbauer absorption measurements have been made at room temperature on 57Fe in iron sodium silicate glasses containing 3–15 mol% Fe 2O 3 and various iron alkali silicate crystals in order to study the state of iron in these glasses. The spectra of all the glasses gave one doublet with a quadrupole splitting varying from 0.73–0.78 mm s −1, while those of Na 2O · Fe 2O 3 · 4 SiO 2 and 5 Na 2O · Fe 2O 3 · 8 SiO 2 crystals showed much smaller quadrupole splitting, 0.28 mm s −1 and 0.10 mm s −1, respectively, and an asymmetrical doublet of much narrower linewidth. When sodium was replaced by other alkali metals of larger size, such as K and Cs, in MFeSi 2O 6 and MFeSi 3O 8 crystals, the quadrupole splitting became wider and approached to 0.73 mm s −1. Such a variation was not observed for glasses. These results suggest that a larger number of non-identical sites exist in iron sodium silicate glasses than in the corresponding crystals. 相似文献
9.
The electrical and dielectric properties for three series of MoO 3–Fe 2O 3–P 2O 5 and one series of SrO–Fe 2O 3–P 2O 5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO 3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe 2O 3 content and Fe(II)/Fe tot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe 2O 3 content in MoO 3–Fe 2O 3–P 2O 5 glasses with O/P at 3.5 the dc conductivity, σ dc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe 2O 3 and is independent of the MoO 3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σ ac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO 3. On the other hand, the dc conductivity for MoO 3–Fe 2O 3–P 2O 5 glasses with O/P > 3.5 increases with the substitution of MoO 3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ′(ω) with increasing MoO 3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe 2O 3–P 2O 5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
10.
V 2O 5 gels containing up to 18 mol% of TiO 2 were obtained through the simultaneous hydrolysis of alkoxides in ethanol solution. V 2O 5 gels containing Na 2O or Li 2O were obtained through the ion exchange method. The crystallization temperature, Tcr, of the gels increased and the H 2O content of the gels decreased by the addition of TiO 2 or Na 2O. These additives seem to stabilize the amorphous state of the gels. On the other hand, Tcr and the H 2O-content slightly varied with the addition of Li 2O. No ionic polarization was observed in coating films of the gels dried at temperatures below Tcr. The dc conductivity of the films was anisotropic, and increased with the addition of Li 2O or Na 2O. However, it decreased with increasing TiO 2 content. The fiber-like structure of gels was observed by TEM. The gels obtained from alkoxides were thin and short in comparison with the gels obtained through the ion exchange method. 相似文献
11.
Appropriate glass compositions of the Na 2O---Al 2O 3---SiO 2 system and glass melting technology were investigated. The dependence of some factors, such as composition of molten salts, time and temperature of ion exchange treatment on the modulus of rupture was studied. As expected, the coefficient of interdiffusion is a function of concentration and has the mixed-alkali effect. The order of the interdiffusion coefficient is 10 −6 cm 2/s. The effect of binary and ternary salt baths on the surface controlled crystallization was reported. The experimental data showed that there is a series of technological advantages from applying molten salts of the ternary system Li 2SO 4---Na 2SO 4---K 2SO 4 in comparison with the binary system Li 2SO 4---Na 2SO 4. 相似文献
12.
Diffusion coefficients of iron were measured in glass melts with the basic compositions 5Na 2O · xMgO · (15− x)CaO · yAl 2O 3 · (80− y)SiO 2 with x=5, 10 and y=0, 5, 7.5, 10 and 15. The melts were doped with 0.25 mol% Fe 2O 3 and studied in the temperature range from 1000 to 1600 °C using square-wave voltammetry. The voltammograms exhibited distinct peaks attributed to the reduction of Fe 3+ to Fe 2+, from which peak currents mixed diffusion coefficients of iron were calculated. Diffusion coefficients in all melt compositions which did not show crystallization could be fitted to Arrhenius equation. The diffusivities measured in different melt compositions were related to the same viscosity, i.e. not the same temperature. Increasing the alumina concentration from 5 to 10 mol% resulted in an increase of the viscosity corrected diffusivities. At further increasing alumina concentrations, the diffusivities get smaller again. This can be explained by the stabilizing effect of Na + and Ca 2+ on FeO −4 and AlO −4-tetrahedra, which strengthens the incorporation of Fe 3+ into the glass structure. 相似文献
13.
11B Fourier transform spectra have been used to study the structure of Na 2O---B 2O 3---SiO 2 glasses of mid-alkali content. Based on the measurements of the fraction N4 of four-coordinated borons, it has been found that for K = mol.% SiO 2/mol.% B 2O 3 8 and R = mol.% Na 2O/mol.% B 2O 3 = 1, N4 is obviously smaller than 1 rather than equal to 1 as assumed in the relevant literature. Only when R reaches a value appropriately greater than 1, can the case where N4 = 1 occur. A structural model suggested in this paper can satisfactorily explain the fact. 相似文献
14.
Single crystals of ruby have been obtained from fluxed melts based on the systems Li 2O–MoO 3, Li 2O–WO 3, Na 2O–WO 3, 2PbO–3V 2O 5, PbO–V 2O 5–WO 3, PbF 2–Bi 2O 3 and Na 3AlF 6 by both the TSSG method and spontaneous crystallization at the temperatures 1330–900 °C. Al 2O 3 solubility has been measured for the flux composition of 2Bi 2O 3–5PbF 2 in the temperature range 1200–1000 °C and dissolution enthalpy has been defined as 29.4 KJ/Mol. The composition of grown crystals was studied by electron microprobe analysis. The synthetic ruby contains from 0.51 to 6.38 at% of chromium admixture depending on the crystal growth conditions. Experimental results on growth conditions, composition and morphology of grown crystals are presented for each flux and temperature interval. 相似文献
15.
Raman spectra were measured of rapidly quenched glasses and the corresponding liquids in binary and ternary (pseudobinary) systems composed of Li 2O and several glass-forming oxides such as B 2O 3, P 2O 5, and/or SiO 2. The fractions of the various structural units present were determined from the deconvoluted Raman peaks. Glasses with large amounts of Li 2O were composed of discrete structural units such as ortho-oxoanions and pyro-oxoanions. Based on these data the structural units in the glasses and the corresponding liquids were identical, although in some cases those in the corresponding crystals were different. In the pseudobinary systems combining pyro-oxosalts of lithium borate, phosphate and silicate, non-bridging oxygens were preferentially formed at the phosphate structural units rather than at the borate or silicate structural units. This order of preference was consistent with that of the acidity of the glass-forming oxides in the liquids. 相似文献
16.
Solid solutions of Nd xLa 2−xcaB 10O 19 with different Na 3+ concentration have been synthesized by substituting Nd 3+ for La 3+ in La 2CaB 10O 19 Powder X-ray diffraction analysis shows that Nd 3+ is easy to incorporate into the crystal. Single crystal nd xLa 2−xCaB 10O 19 (NLCB) in centimeter size has been grown by Kyropoulos method. The crystal has strong absorption around 580nm and 805nm. The fluorescence spectra indicate that there is an energy transition at 1.06μm. And the SHG of NLCB is about the twice as that of KDP. These favorable features make NLCB a candidate for laser NLO multifunctional materials. 相似文献
17.
Phase relation of Bi 2O 3---SiO 2 system was evaluated experimentally from DTA and XRD measurements and its stable and metastable phase diagrams were proposed. Although BSO melts near-congruently at 1025°C in the stable phase equilibrium, its melt crystallizes to form metastable phase Bi 2SiO 5 in accordance with the metastable phase diagram while cooling. Therefore, BSO couldn't nucleate and crystallize spontaneously without crystal seed and only Bi 2SiO 5 crystallized at about 850°C with significant supercooling during Bridgman growth. BSO single crystal with 20×20×100mm 3 was grown in a vertical Bridgman furnace with a BSO seed according to its phase diagram. The measuring results of scintillation properties of BSO specimen show that its decay constant is 91 ns (about 1/3 of BGO) and light output is 23% of BGO. 相似文献
18.
We obtained the chemical shielding constants of 29Si in Li 2S–SiS 2 glass system on the basis of molecular orbital calculations. The relative chemical shieldings calculated at the HF/6-31G* level is −16.1 and −23.8 ppm for E(1) and E(0), respectively. These calculations are in good agreement with the previous NMR study: σ( E(2))>σ( E(1))>σ( E(0)). It is found theoretically that incorporation of Li 2S into SiS 2 does not influence the 29Si chemical shift, while incorporation of Li 2O into SiO 2 does to a significant extent. It is also found that the existence of oxygen in Li 2S–SiS 2 glasses increases the chemical shielding of 29Si by about 25 ppm, which is in good agreement with the experimental result. 相似文献
19.
Crystallization of In 2O 3 occured in closed porcelain crucibles in air at 960–1200°C by vapor phase reaction of In 2O or In vapor with the oxygen diffusing into the system. The In 2O or In vapors were thermally generated from mixtures such as graphite/In 2O 3, graphite/In, In 2O 3/In and graphite/In 2O 3/In. The graphite/In 2O 3 system at a mole ratio of 30/1 and 1000°C produced yellow, transparent needle crystals with a maximum size of 0.5 X 0.5 X 8 mm and electrical resistivity of 5.5 X 10 -2 ω cm at 25°C. 相似文献
20.
Small-angle X-ray scattering (SAXS) measurements on V 2O 5· nH 2O sols and gels, prepared by dissolving V 2O 5 glass into water at room temperature, show that there are V 2O 5 polymeric fibers entangled like random coils in the sol of n 5000, while the deviation from the random coil behavior occurs in the dilute sol of n 6000. A Bragg peak appears at the scattering vector h 0.02 Å−1 to be superimposed on an asymptotic h−2-course in the SAXS curve of the concentrated sol of n 680. This means that the spatial correlation between V2O5 polymeric fibers takes place even in the fluid state. V2O5·nH2O sols completely lose fluidity at n 250 to transfer to the gel state, where V2O5 polymeric fibers begin to pile up in the parallel with a substrate surface. Such a layer structure is preserved up to the gel of n 4. However, V2O5 polymeric fibers are randomly oriented within each layer. 相似文献
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