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1.
We report on the top-seeded solution growth of LiB 3O 5 from an excess B 2O 3 solution. Parameters investigated include the Li 2O/B 2O 3 ratio, rotation rate, pulling rate, cooling rate, and seed direction. With careful control of the above parameters, we have grown clear crystals of 25 × 30 × 20 mm in size. Selected nonlinear optical properties of these crystals are reported. Observations concerning the occurrence of unstable growth (inclusions, hopper growth) are discussed, and methods to eliminate the unstable growth are suggested. 相似文献
2.
Single crystals of PbMg 1/3Ta 2/3O 3 (PMT) were grown by the flux method. The PbO–Pb 3O 4–B 2O 3 system was used as a solvent. Transparent and light yellow PMT single crystals of rectangular shape and dimensions up to 10×6×4 mm 3 were obtained. For the applied growth conditions only, the crystals of the perovskite structure were grown. X-ray diffraction tests showed that at room temperature PMT exhibits cubic symmetry with lattice parameter a=4.042(1) Å. Dielectric studies pointed to relaxor properties of PMT. The characteristic broad and frequency-dependent maximum of dielectric permittivity was observed at 179.7 K (1 kHz). 相似文献
3.
We report on the successful growth of β-Ga 2O 3 single crystals using the Czochralski method. Model calculations show that the gas phase consists of Ga 2O, GaO or Ga independent of the ratio of oxygen and Ar or N 2. We find that for growing single crystals the evaporation has to be suppressed by a finite amount of oxygen. A CO 2/Ar gas atmosphere was found to meet this requirement. 相似文献
4.
Glasses in the system Na 2O/B 2O 3/Al 2O 3/In 2O 3 were melted and subsequently tempered in the range from 500 to 700 °C. Depending on the chemical composition, various crystalline phases were observed. From samples without Al 2O 3, In 2O 3 could not be crystallized from homogeneous glasses, because either spontaneous In 2O 3 crystallization occurred during cooling, or other phases such as NaInO 2 were formed during tempering. The addition of alumina, however, controlled the crystallization of In 2O 3. Depending on the crystallization temperature applied, the crystallite sizes were in the range from 13 to 53 nm. The glass matrix can be dissolved by soaking the powdered glass in water. This procedure can be used to prepare nano-crystalline In 2O 3-powders. 相似文献
5.
Gallate glasses containing no conventional glass formers were obtained in the systems (Na 2O, K 2O or Cs 2O)-Ta 2O 5---Ga 2O 3 and (Sr or BaO)-Ta 2O 5---Ga 2O 3 by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga 3+ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure. 相似文献
6.
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
7.
A solvothermal route has been developed to synthesize K 2V 3O 8 nanorods via the reduction of V 2O 5 using ethanol as the reducing agent as well as the solvent at 200°C. X-ray diffraction and selected area electron diffraction analysis revealed that the as-synthesized products are of tetragonal structure K 2V 3O 8. Transmission electron spectroscopy image showed that the obtained K 2V 3O 8 comprises rod-like nanocrystallites. The formation mechanism of K 2V 3O 8 was studied. 相似文献
8.
The high viscosity in melts of the Li 2O---B 2O 3 system makes it very difficult to grow large crystals of lithium triborate. The viscosity and IR characteristics of molten li 2O---B 2O 3 system are reported in this paper. When the temperature increases the viscosity of li 2O---B 2O 3 system decreases and follows an Arrhenius-type relationship. With an increasing 13203 ratio in Li 2O---B 2O 3 melts, the viscosity rises gradually to a maximum with a composition Li 2O: 3.513203 then it falls rapidly. In order to find active agents to reduce the viscosity, Na 2O, NaCl, LiF, P205, M003, W03 etc oxides were added to Li 2O---B 2O 3 samples respectively and investigated using the orthogonal method. The experimental results show that the addition of acidic oxides can significantly decrease the viscosity in the Li 2O---B 2O 3 system. For Li 2O: 4.513203, an ideal additive agent is 20wt% Li 2O:: 2MoO 3. Near the composition for crystal growth, the percentage reduction of viscosity is 62.2%. The IR spectra of Li 2O---B 2O 3 system revealed that the BO 4−/NO 3− ratio is reduced in the melt using Li 2O: 2MoO 3 as an additive. It is proposed that the M003 reduced the concentration of bridging oxygen atoms of BO 4−. The change of structure explains the decline in the viscosity. In the crystal structures of lithium triborate, the matrix spaces are so small that larger other cations than Li+ are very difficult to enter the crystal matrix. So the use of additive agents to reduce the viscosity is a possible method if no new phase appears. 相似文献
9.
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
10.
YBa 2Cu 4O 8 is a stoichiometric oxide superconductor of Tc80 K. Unlike YBa 2Cu 3O 7−δ, this compound is free from oxygen vacancy or twin formation and does not have any microscopic disorder in the crystal. Doping with Ca raises its Tc to 90 K. The compound is a promising superconductor for technological application. Up to now, single crystals have not been grown without using specialized apparatus with extremely high oxygen pressure up to 3000 bar and at over 1100 °C due to the limited range of reaction kinetics of the compound. This fact has delayed the progress in the study of its physical properties and potential applications. We present here a simple growth method using KOH as flux that acts effectively for obtaining high-quality single crystals in air/oxygen at the temperature as low as 550 °C. As-grown crystals can readily be separated from the flux and exhibit a perfect orthorhombic morphology with sizes up to 0.7×0.4×0.2 mm 3. Our results are reproducible and suggest that the crystals can be grown using a conventional flux method under ambient condition. 相似文献
11.
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
12.
High-quality and crack-free Y 2O 3 single crystals containing low concentrations of Tm 3+, Tb 3+ and Yb 3+ were obtained. The crystals were grown in the form of monocrystalline fibers by using a floating zone method with laser heating (laser-heated pedestal growth). 相似文献
13.
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
14.
Large-size single crystals of β-Ga 2O 3 with 1 inc in diameter have been grown by the floating zone technique. The stable growth conditions have been determined by the examination of the crystal structure. Wafers have been cut and fine polished in the (1 0 0), (0 1 0) and (0 0 1) planes. These were highly transparent in the visible and near UV, as well as electrically conductive, indicating the potential use of β-Ga 2O 3 as a substrate for optoelectic devices operating in the visible/near UV and with vertical current flow. 相似文献
15.
The vapor phase epitaxy of thin epilayers of VO 2 and V 1−xCrxO 2 on TiO 2 transparent substrates is described. Chemical vapor deposition occurs by reacting a (VOCL 3/CrO 2Cl 2/H 2O/H 2) mixture at about 800°C using argon as a carrier gas. The preparation of pure VO 2 requires special care to make it homogeneously stoichiometric and to obtain steep concentration profiles at the TiO 2/VO 2 interface. Layers were obtained which had electrical and optical properties comparable to the best bulk crystals grown by other techniques. Homogeneous solid solutions of V 1−xCr xO 2 epilayers were also grown for the first time in the range o < x < 0.17. Chromium concentration and homogeneity were determined by electron microprobe analysis. The separation coefficient k was also found to vary with x. It is close to unity below x = 0.001 and above this value Cr is incorporated more easily. High quality heteroepitaxial layers (1 cm 2 area, 1 to 30 μm thickness) of V 1−xCr xO 2 have for the first time allowed the measurement of the optical absorption coefficient. 相似文献
16.
Growth of completely flux-separated YBa 2Cu 3O 6 + δ (referred to as 123 phase) crystals using a novel technique is described. The technique employs a modification of the seed pulling method commonly used in crystal growth. The crystals are grown in the temperature range of 960–1000°C using a BaCuO 2 flux. A 123 flux ratio of 1:5 is maintained. Photographs of the crystals and photomicrograph of the surfaces are presented to show complete flux-separation of the crystals measuring 6 mm × 3 mm × 1 mm. The Raman spectra recorded on the as-grown crystals show that they are in the tetragonal phase. Magnetic susceptibility measurements on crystals annealed in an oxygen atmosphere show a superconducting transition starting at 71 K. The present technique offers a possibility of growing large, completely flux-separated crystals of 123 for superconductivity research. 相似文献
17.
We investigated the dependence of the Y 2O 3 film growth on Si surface at initial growth stage. The reflection high-energy electron diffraction, X-ray scattering, and atomic force microscopy showed that the film crystallinity and morphology strongly depended on whether Si surface contained O or not. In particular, the films grown on oxidized surfaces revealed significant improvement in crystallinity and surface smoothness. A well-ordered atomic structure of Y 2O 3 film was formed on 1.5 nm thick SiO 2 layer with the surface and interfacial roughness markedly enhanced, compared with the film grown on the clean Si surfaces. The epitaxial film on the oxidized Si surface exhibited extremely small mosaic structures at interface, while the film on the clean Si surface displayed an island-like growth with large mosaic structures. The nucleation sites for Y 2O 3 were provided by the reaction between SiO 2 and Y at the initial growth stage. The SiO 2 layer known to hinder crystal growth is found to enhance the nucleation of Y 2O 3, and provides a stable buffer layer against the silicide formation. Thus, the formation of the initial SiO 2 layer is the key to the high-quality epitaxial growth of Y 2O 3 on Si. 相似文献
18.
Metastable crystals of Li 2Ti 3O 7 of dimensions up to a diameter of 20 mm and a length of 20 mm have been grown by the Czochralski method from oriented seeds. The effects of seed orientation, growth atmosphere and dopant on crystal growth have been studied. Phase transition processes in the crystals and the H phase structure have been measured. Optical and acoustic properties of the crystals have also been determined. 相似文献
19.
Large single crystals of
quasi-one-dimensional antiferromagnetic spin system NaV 2−zTi zO 5 (0 z0.06) have been successfully grown by a flux method. We present growth conditions together with a characterization of the single crystals by means of X-ray powder diffraction, energy dispersive X-ray (EDX) analysis and magnetic susceptibility measurements. 相似文献
20.
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
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