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1.
Ce, Nd and Eu doped BSO crystals 20×20× 100mm 3 in size have been gown by vertical Bridgman method, and the doped effects on radiation resistance of BSO have also been studied for the first time. Nd and Eu dopns were found to improve the radiation resistance of BSO. However, Cc and Nd dopings degrade the light output of BSO except that Eu doping has almost no effect on it. Therefore, Eu may be the most promising dopant candidate for improving the scintillation properties of BSO crystal. 相似文献
2.
Dislocations in Bi 12SiO 20 (BSO) crystals, annealed in a reducing atmosphere, were directly observed by conventional light microscopy in transmission mode. A one-to-one correspondence between dislocations and etch pits was observed. 相似文献
3.
Bi 20TiO 32 in the form of nanocones are reported for the first time, which have been found during the formation of Bi 2Ti 2O 7 nanocrystals. Bi 20TiO 32 nanocones were prepared by metalorganic decomposition technique. From X-ray patterns, it was found that Bi 20TiO 32 is a metastable phase, and can transform gradually into Bi 2Ti 2O 7 phase with the annealing time increasing at a temperature of 550°C. The image of field emission scanning electron microscopy shows that the lengths of the nanocones are up to several micrometers and the diameters of cusps range from 20 to 200 nm. The studies of transmission electron microscopy show that the nanocones are crystalline Bi 20TiO 32. The growth mechanism of Bi 20TiO 32 nanocones has been proposed, which is similar to the vapor–liquid–solid growth mechanism. 相似文献
4.
Phase relations around langasite (LGS, La 3Ga 5SiO 14) were studied on the basis of phase assemblage observed during calcination and crystallization process of samples of various compositions in the ternary system La 2O 3–Ga 2O 3–SiO 2. A ternary compound of apatite structure, La 14Ga xSi 9–xO 39–x/2 was found for the first time. Crystallization of this compound was observed in the cooling process of molten samples of stoichiometric LGS as well as LGS single crystal, demonstrating that LGS is an incongruent-melting compound. A phase diagram was established primarily based on the crystallization sequence in the cooling process. 相似文献
5.
Ce-doped SrGa 2S 4 compound is expected as a new host material of blue EL devices. However, the basic properties of bulk single crystals have not been fully clarified, since this compound has been mostly synthesized in the form of polycrystals or thin films. Here, we firstly present the pseudo-binary phase diagram of the SrS–Ga 2S 3 system constructed in accordance with our DTA data for single-crystal growth of SrGa 2S 4. It is shown that SrGa 2S 4 compound has a congruent melting point and a eutectic reaction in the side of excess of Ga 2S 3 concentration. On the basis of the phase diagram, single crystals of SrGa 2S 4 are grown using Ga 2S 3 as a self-flux in a horizontal Bridgman furnace. Colorless and transparent crystals having a typical size 2×2×2 mm 3 are obtained. 相似文献
6.
Tellurite containing vanadate (50− x)V 2O 5– xBi 2O 3–50TeO 2 glasses with different bismuth ( x=0, 5, 10, 15, 20 and 25 wt%) contents have been prepared by rapid quenching method. Ultrasonic velocities (both longitudinal and shear) and attenuation (for longitudinal waves only) measurements have been made using a transducer operated at the fundamental frequency of 5 MHz in the temperature range from 150 to 480 K. The elastic moduli, Debye temperature, and Poisson’s ratio have been obtained both as a function of temperature and Bi 2O 3 content. The room temperature study on ultrasonic velocities, attenuation, elastic moduli, Poisson’s ratio, Debye temperature and glass transition temperature show the absence of any anomalies with addition of Bi 2O 3 content. The observed results confirm that the addition of Bi 2O 3 modifier changes the rigid formula character of TeO 2 to a matrix of regular TeO 3 and ionic behaviour bonds (NBOs). A monotonic decrease in velocities and elastic moduli, and an increase in attenuation and acoustic loss as a function of temperature in all the glass samples reveal the loose packing structure, which is attributed to the instability of TeO 4 trigonal bipyramid units in the network as temperature increases. It is also inferred that the glasses with low Bi 2O 3 content are more stable than with high Bi 2O 3 content. 相似文献
7.
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
8.
Crystal growth conditions of Bi 2Te 3 narrow bandgap semiconductors have been studied using molecular beam epitaxy method. It was applied to the growth of Bi 2Te 3 on Bridgman single-crystal substrate Sb 2Te 3. Substrate ingots were taken from the natural cleavage along the (0001) plane. The deposited conditions have been studied as a function of substrate temperature ( Ts) and flux ratio ( FR= F( Te)/ F( Bi)). The quality of deposited layers was controlled by X-ray diffraction, scanning electron microscope (SEM), secondary ion mass spectroscopy (SIMS) depth profiling and energy-dispersive X-ray (EDX) microanalyser. The sticking coefficients Ks(Te) and Ks(Bi) of the elements that compose Bi 2Te 3 were determined. It was found that the stoichiometry of deposited layers depended on substrate temperature and flux ratio. It was observed that all deposited layers were single-crystal in the orientation of their substrates with a small shift due to the stress in layer. 相似文献
9.
The part of the CdCr 2Se 4-CdCl 2 phase diagram within the range of 75–100 mole% of CdCl 2 has been examined. The composition CdCr 2Se 4 · CdCl 2 was found to be stable below 542°C. The crystallisation processes of CdCr 2Se 4 spinel for two mixture compositions: 88% CdCl 2-12% CdCr 2Se 4 and 80% CdCl 2-20% CdCr 2Se 4 have been carried out and the parameters of CdCr 2Se 4 crystal growth from the CdCl 2 flux were determined. 相似文献
10.
Pb[(Zn 1/3Nb 2/3) 0.91Ti 0.09]O 3 (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg 1/3Nb 2/3) 0.69Ti 0.31]O 3 (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d33, remnant polarization Pr, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm 2, and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions. 相似文献
11.
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
12.
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
13.
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
14.
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
15.
Glasses of compositions 5ZrO 2·5SiO 2(ZS), 5ZrO 2·Al 2O 3·4SiO 2(ZAS) and 5 5ZrO 2·0.5Al 2O 3·0.5Na 2O·4SiO 2(ZANS) were prepared by the sol-gel process from metal alkoxides and sintered to make glass-ceramics. Tetragonal ZrO 2 was precipitated by heat treatment at 900 to 1300°C. The activation energy for tetragonal ZrO 2 crystal growth was extremely high in Al 2O 3 containing glasses. ZAS and ZS were sintered to the near theoretical densities above 1200°C, at which the predominant phase was tetragonal ZrO 2. On the other hand, for ZANS, high densification was not attained owing to the large pores enclosed by the glass phase. Strength and fracture toughness increased with the densification and the crystal growth of tetragonal ZrO 2, reaching 450 MPa and 9 MN/m 1.5, respectively. 相似文献
16.
The phase equilibrium and the crystallization process of lead iodide (PbI 2) melt have been primarily investigated according to the lead–iodine phase diagram. It is found that the iodine evaporation and the segregated lead deposition are the two important factors that affect the PbI 2 crystal quality. The new method of Pulling U-type quartz growth ampoule has been made to impede the decomposition of PbI 2 and the vaporization and condensation of iodine. An orange and translucent PbI 2 single crystal of large size was obtained by the improved growth method, i.e. U-type ampoule pulling. Resistivity of the as-grown crystal is up to 4×10 11 Ω cm, and IR transmission is up to 45% in the region from 7800 to 450 cm −1. Therefore, the improved growth method is a promising convenient new method for the growth of high quality PbI 2 crystals. 相似文献
17.
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
18.
Post-annealing effects on superconducting characteristics have been studied in Bi 2Sr 2Ca 1Cu 2O x single crystals grown by a conventional flux method. Also, favorable growth conditions and the effect of the pre-sintering process on the starting materials for flux growth have been examined. The best superconducting behavior is obtained in post-annealed crystals grown from pre-sintered powder materials. The critical current density Jc estimated from magnetization hysteresis in annealed crystals grown with pre-sintered materials is roughly 8×10 5 A/cm 2 ( Hc) and 5×10 4 A/cm 2 ( Hc) at 4.2 K at zero field. 相似文献
19.
The effect of alumina on the phase separation and the crystallization of the glasses of composition (mol%) 18ZnO·30B 2O 3·52SiO 2 and O-40 Al 2O 3 was studied using an electron microscope and IR spectroscopy. The main crystalline phase appears in the microphase for which the compositions are not nearer to the crystal stoichiometry than the mean. The addition of Al 2O 3 suppresses the immiscibility but enhances the crystallizability. 相似文献
20.
Metal organic chemical vapor deposition has been investigated for growth of Bi 2Te 3 films on (0 0 1) GaAs substrates using trimethylbismuth and diisopropyltelluride as metal organic sources. The results of surface morphology, electrical and thermoelectric properties as a function of growth parameters are given. The surface morphologies of Bi 2Te 3 films were strongly dependent on the deposition temperatures. Surface morphologies varied from step-flow growth mode to island coalescence structures depending on deposition temperature. In-plane carrier concentration and electrical Hall mobility were highly dependent on precursor's ratio of VI/V and deposition temperature. By optimizing growth parameters, we could clearly observe an electrically intrinsic region of the carrier concentration at the temperature higher than 240 K. The high Seebeck coefficient (of −160 μVK −1) and good surface morphology of this material is promising for Bi 2Te 3-based thermoelectric thin film and two-dimensional supperlattice device applications. 相似文献
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