共查询到20条相似文献,搜索用时 31 毫秒
1.
Yu. B. Bolkhovityanov R. I. Bolkhovityanova V. I. Yudaev 《Crystal Research and Technology》1980,15(4):387-394
The initial stages of growth of GaAs–InGaAsPvar–InxGa1−xAs heterostructures (x = 0.1 and 0.17) were investigated for the equilibrium-cooling method of LPE growth. Similar investigations were carried out for GaAs–InGaAsPvar–In0.05Ga0.95As heterocompositions, but for the step-cooling technique. The scheme of growing of In0.17Ga0.83As films of GaAs substrates with several intermediate buffler InGaAsPvar layers is represented. These heterostructures were shown to have less than 106 cm−2 dislocation density on the overall area of the film (> 2 cm2). 相似文献
2.
《Journal of Non》2007,353(16-17):1612-1617
Sodium borosilicate glasses containing different amounts of BaO were prepared by a conventional melt quench method and characterized for their structural aspects by 29Si, 11B NMR and IR spectroscopy. From 29Si MAS NMR studies, it has been inferred that these glasses consist of Q2 and Q3 structural units of silicon and that the addition of BaO results in the marginal conversion of Q3 to Q2 structural units. There is no direct interaction between Ba2+ ions and boron structural units, as revealed by the identical values of the relative concentration of BO3 and BO4 structural units and quadrupolar coupling constant values for the BO3 structural units. The identical values of glass transition temperature and vibrational frequencies corresponding to Si–O–Si/Si–O–B and B–O linkages of all the samples further support this. As the borosilicate network is unaffected, the systematic increase in the values of thermal expansion coefficient with increase in BaO content has been attributed to the increase in the relative concentration of less rigid Ba–O linkages compared to the more rigid Si–O and B–O linkages in the glass. Such studies will be useful for the development of matrices for the management of nuclear waste generated during the reprocessing of the spent fuel from thoria based reactors. 相似文献
3.
A. Monteil M. El-Jouad G. Alombert-Goget S. Chaussedent N. Gaumer A. Mahot A. Chiasera Y. Jestin M. Ferrari 《Journal of Non》2008,354(42-44):4719-4722
The SiO2–HfO2 binary system is recognized as a promising candidate for Erbium-doped waveguides amplifiers fabrication. Recently, it was demonstrated that Er3+-activated 70SiO2–30HfO2 planar waveguides with valuable optical and structural properties can be prepared by sol–gel technique with dip-coating processing. The important role played by hafnium in the silica network was evidenced by the particular spectroscopic properties presented by Er3+-ions in the silica–hafnia planar waveguides. In this work we present preliminary results on HfO2–SiO2 bulk xerogels doped with Eu3+ ions, with the aim to go inside the role of hafnium on the rare earth ions local environment. Spectroscopic measurements of the Eu3+ photoluminescence emission are given. Numerical simulations by the molecular dynamics method have been performed showing clearly a phase separation for the HfO2 richer samples. Moreover it is found than the rare earth-doping ions stay preferentially in hafnium rich domains, thus explaining why the rare earth spectroscopic properties are strongly modified. 相似文献
4.
Sangen Zhao Guochun Zhang Kai Feng Jun Lu Yicheng Wu 《Crystal Research and Technology》2012,47(4):391-396
Bulk BPO4 crystals have been successfully grown from high temperature solution of BPO4, Li2O, and MoO3 in the molar ratio of 2.3:1:1.3 by the top‐seeded solution growth (TSSG) method using [101]c orientation seeds. There are no visible scattering centers and impurity of Mo in the as‐grown BPO4 crystals, whose optical homogeneity reaches up to 1.6×10–5/cm. BPO4 possesses a specific heat of 0.50–1.00 J·g–1·K–1 in the temperature range from 298 to 698 K and exhibits strong anisotropic thermal expansion behavior with αa = 14.2 × 10–6 K–1 and αc = ‐4.0 × 10–7 K–1. Moreover, the thermal conductivity coefficients are calculated to be κa = 62.4 W·m–1·K–1 and κc = 51.5 W·m–1·K–1, which are remarkably larger than those of some commonly used borates. The measured dielectric constants, εa and εc, are 4.8 and 6.1, respectively, and the ionic conductivity coefficients, σa = 4.3 × 10–8 S/cm and σc = 9.5 × 10–8 S/cm, are several orders of magnitude lower than that of LiB3O5 (LBO). (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
5.
《Journal of Non》2007,353(13-15):1402-1406
Fluorophosphate glasses of composition P2O5–K2O–MgO–Al2O3–AlF3 and P2O5–K2O–MgO–Al2O3–BaF2 were prepared with different Nd3+ ion concentrations. The absorption and emission spectra in the UV–VIS–NIR region were measured for these glasses. Judd–Ofelt analysis has been carried out using the absorption spectra of 1.0 mol% Nd3+-doped glasses to evaluate the radiative properties for some luminescent levels of the Nd3+ ion. The stimulated emission cross-sections of the 4F3/2 → 4I11/2 laser transition for the present glasses are found to be higher than for other Nd3+-doped glasses. Branching ratio calculations also revealed the potentiality of the 4F3/2 → 4I11/2 transition for laser action in these glasses. The observed concentration quenching of the lifetime of the 4F3/2 level is explained as a result of cross-relaxation process between the Nd3+ ions. 相似文献
6.
Transparent rare-earth Eu3+-doped ZnO–Ga2O3–SiO2 nano-glass-ceramics were obtained by a sol–gel method. X-ray diffraction and transmission electron microscopy were used to characterize the as-synthesized materials. Results showed that ZnGa2O4 nanocrystals with the size of 5 nm were precipitated from ZnO–Ga2O3–SiO2 system and dispersed in the SiO2-based glass when the heat-treatment temperature was up to 800 °C. Photoluminescence characterization of Eu3+-doped ZnO–Ga2O3–SiO2 nano-glass-ceramics was carried out and the results show that the as-synthesized material display intense emission at 615 nm belonging to 5D0 → 7F2 transition. 相似文献
7.
《Journal of Non》2006,352(26-27):2778-2782
10Al2O3–5B2O3–85SiO2–xSm2O3 glasses were prepared by the sol–gel method. The emission spectra of the glasses indicate that the quench concentration of the Sm3+ ions is about 0.2 mol%. The emission spectra of the glasses after high-temperature treatment with H2 gas exhibit the coexistence of the Sm3+ and Sm2+ ions. We observed the strong emission line of the Sm2+ ions and the emission band of the non-bridging oxygen hole center when the glasses were exposed to a femtosecond laser. It indicates that some Sm3+ ions were reduced to Sm2+ ions by femtosecond laser pulses and non-bridging oxygen hole centers were formed. The 5D0–7F0 emission line of the Sm2+ ions by femtosecond laser irradiation shows a red shift, compared with the emission of the Sm2+ ions by reduction with H2 gas. The strong absorption band and weak, sharp absorption lines in the range from the UV to IR come from charge transfer and the transition from the 6H5/2 state to the various excited states of the Sm3+ ions. The reduction mechanism of Sm3+ ions is discussed. 相似文献
8.
A.J. Barbosa L.J.Q. Maia A.M. Nascimento R.R. Gonçalves G. Poirier Y. Messaddeq S.J.L. Ribeiro 《Journal of Non》2008,354(42-44):4743-4748
Planar waveguides were prepared by Ag+/K+ ? Na+ ion-exchange on Er+3-doped GeO2–ZnO–Na2O–Li2O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag+ ion-exchange time. The optimized planar waveguides show an effective diffusion depth (d) of 2.95 μm and well confined propagating TE0 and TM0 modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag+ ? Na+ ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag+ was also observed. 相似文献
9.
《Journal of Non》1997,209(3):305-308
Differences in crystalline phases between glass-ceramics and sintered ceramics in the K2O–Nb2O5–TeO2 system have been examined, particularly to obtain information on the role of Te valence on crystallization behaviors of TeO2-based glasses. In glasses or glass-ceramics, the valence of Te4+ is retained even during heat-treatment up to around 600°C, leading to the formation of crystalline phases containing Te4+, e.g., the face-centered cubic crystalline phase. In a powder sintering method, Te4+ is easily oxidized to Te6+ during sintering at around 600°C in air and compounds such as KNbTeO6 in which Te6+ is present are formed. 相似文献
10.
In this study, the effect of Mg substitution on structural, magnetic and electrical properties of La0.75Sr0.25Mn1?xMgxO3 and La0.75Sr0.25?xMgxMnO3 (nominal compositions) samples are investigated by XRD, Ac susceptibility and electrical resistivity measurements. It is found that Mg does not replace La in the perovskite lattice. Also the results show that by increasing Mg doping levels, the paramagnetic–ferromagnetic and metal–insulator transition temperatures decrease. The reason for decreasing transition temperatures with increasing Mg concentration is, that the long-range FM order has been destroyed by the Mg, which is randomly occupying Mn site. This leads to the suppression of double-exchange interaction in the Mn3+–O–Mn4+ networks. Also the reentrant spin glass (RSG) state accompanied by FM transition, exists in high doped samples. The RSG state could be understood on the basis of double exchange ferromagnetic interaction in Mn3+–O–Mn4+ and super-exchange antiferromagnetic interaction in the Mn4+–O–Mn4+ networks. 相似文献
11.
I. D. Olexeyuk P. I. Babidorich I. S. Rez Yu. V. Voroshilov 《Crystal Research and Technology》1978,13(4):409-412
Growing of large (Ø 25–30 mm, L = 50–60 mm) optically homogenous single crystals of Tl3AsS4 using the Bridgman-Stockbarger method is described. Tl3AsS4 is orthorhombic (Pnma), a = 8.85 ± 0.03, b = 10.86 ± 0.03, c = 9.18 ± 0.03 Å; z = 4; ϱx = 6.15 g · cm−3; ϱp = 6.15 ± 0,03 g · cm−3, Tm = 424 ± 3°C, Moh's hardness = 3, microhardness and ultrasonics velocity along x, y, z are 65–85 kg · mm−2 and 2.16 – 2.37 · 105 cm · sec−1, respectively. The crystals possess perfect cleavage plane (010). Their transparency range is 0.6–12 microns. – Unsuccessful attempts to obtain Tl3AsS4 and its alloys in the vitreous state were taken. The possibilities of glass formation and boundaries of the vitreous region in the system Tl–As–S based on the characteristic features of the melt forming structural units are analyzed. 相似文献
12.
A. A. Kaminskii K. Ueda A. F. Konstantinova H. Yagi T. Yanagitani A. V. Butashin V. P. Orekhova J. Lu K. Takaichi T. Uematsu M. Musha A. Shirokava 《Crystallography Reports》2003,48(5):868-871
Refractive indices of the nanocrystalline Y3Al5O12 ceramic and a garnet single crystal of the same composition have been measured. In the visible and near IR range (0.4–1.064 μm), the prism method was used; in the medium IR range (2–6.2 μm), the interference method with the use of thin plates was applied. The refractive indices of these crystalline materials are practically the same over the entire spectral range studied and are described by the approximate formula proposed earlier for a single crystal. The parameters of the continuos-wave lasing in the nanocrystalline Y3Al5O12 ceramic doped with Nd3+ and Yb3+ ions measured recently are presented. 相似文献
13.
Raman scattering (RS), photoluminescence (PL) and energy dispersive X‐ray (EDX) experiments have been carried out to investigate residual strain and hence to understand breakage issue in bulk Inx Ga1–x As crystal grown by multi component zone melting (MCZM) method. It is found from a comparison that there is a large discrepancy among the RS, PL and EDX results due to the strain induced by compositional variation in the crystal. The strain induced changes in TOGaAs and PL peak positions are found to be 4.04 cm–1 and 0.097 eV, respectively, for the variation of composition from 0.06 to 0.29 from the seed‐end to the tail‐end of the crystal. By assuming a simple one‐dimensional strain distribution, the strain value corresponding to 4.04 cm–1/ 0.097 eV can be obtained of the order of 10–2, which is large enough for understanding the breakage issue in the crystal investigated here. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
Yuzhi Zhang Jiaguo Yuan Yunzhen Cao Lixin Song Xingfang Hu 《Journal of Non》2008,354(12-13):1276-1280
Photochromic behavior of Li-doped MoO3 sol–gels prepared by the peroxo sol–gel method was studied in details using various experimental techniques, including UV–vis, XRD, Raman, EPR, and XPS. The lithium doping has drastically enhanced the stability of the MoO3 sol–gels. Upon UV-light irradiation from a high-pressure mercury lamp, the Li-doped MoO3 sol turned from yellowish into deep blue, and the sol in ethanol exhibited much more intense color change than the sol in water. The UV-light exposure has the effect of re-arranging the structural units of MoO3 and building up short-range order inside the solid. The formation of a blue colored bronze in the photo-irradiated sols because of the reduction of Mo6+ to Mo5+ is also evidenced by the experimental data. Based on these data, a mechanism for the photochromic behavior is proposed. 相似文献
15.
Tiefeng Xu Feifei Chen Shixun Dai Xiang Shen Xunsi Wang Qiuhua Nie Chao Liu Kai Xu Jong Heo 《Journal of Non》2011,357(11-13):2219-2222
Tellurite glasses from TeO2–Bi2O3–BaO pseudo-ternary system were prepared using a conventional melt-quenching method and its glass-forming region was determined. A series of glasses were selected and their third-order optical nonlinearities (TONL) were measured by employing the Z-scan method at a wavelength of 800 nm with femtosecond laser pulses. The results showed that glass former Te4+ ions exhibited positive influences on the TONL and glass modifiers Ba2+ ions behaved similarly; low concentrated Bi3+ ions as glass modifiers weakened the nonlinearities, but an excess amount of Bi3+ behaved oppositely. FTIR measurements demonstrated that chemical bonds especially Te–Oeq vibrated at a high energy level remarkably promoted the TONL susceptibility χ(3), and the glass sample with the highest Bi2O3 content exhibited the largest χ(3) value which was due to the presence of BiO3 polyhedra. 相似文献
16.
E. V. Kiryanova 《Crystal Research and Technology》2010,45(10):1017-1024
Detailed precision investigation of aqueous solutions of NaBr·2H2O, KBr, RbNO3, and K2SO4 salts showed oscillations of crystal‐solution phase equilibria in the temperature range of 15–45 °C. The maximum deviations from the smooth correlation between the saturation temperature and the salt concentration (up to 4% of concentration and up to 10 °C) were found to correspond to simplest salt‐water ratios. Recently, similar trends were observed for NaNO3, KNO3 and K2CrO4 solutions. Oscillation amplitudes for saturation temperature in the investigated series decreased in the following orders: Na+→K+, Rb+, NH4+ (nitrate systems), CrO42–→SO42– and Br–→NO3– (potassium systems), and NO3–→Br– (sodium systems). Increase in total content of impurities (2‐4‐fold) in solution results in 1.5‐2‐fold elevation of the oscillation amplitudes. A concept of nanoheterophase solution was suggested to account for the observed temperature‐concentration oscillations. The concept is based on the original experimental data on interrelated variation of different properties of aqueous salt solutions depending on their concentrations. Characteristic features of the phase diagrams are discussed and influence of the oscillations on crystal growth is elucidated. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
17.
A new method to determine ac conductivity of amorphous Ge using Al-amorphous Ge–SiO2–P+Si tunnel junctions is presented. Frequency dependence of ac conductivity is found to satisfy the power law in the frequency range between 1 and 50 kHz and the density of localized states at the Fermi level is estimated to be ~ 1.7 × 1020 cm?3 eV?1 which decreases to ~ 4.5 × 1019 cm?3 eV?1 after annealing at 175°C.Temperature dependence of tunneling conductance of Al-amorphous Ge–SiO2–P+Si junctions is appreciable only near zero bias. Zero bias conductance of the junctions obeys the law of Mott; the density of localized states obtained from the law is one order of magnitude smaller than that obtained by ac conductivity measurements, being insensitive to annealing. This behavior of the tunnel junctions differes in many respects from those of Al–Al2O3-amorphous Ge tunnel juntions. 相似文献
18.
The room temperature crystal data, Debye temperature, dark and photoelectrical properties of the Bridgman method grown Tl2InGaTe4 crystals are reported for the first time. The X‐ray diffraction technique has revealed that Tl2InGaTe4 is a single phase crystal of tetragonal body‐centered structure belonging to the space group. A Debye temperature of 124 K is calculated from the results of the X‐ray data. The current‐voltage measurements have shown the existence of the switching property of the crystals at a critical voltage of 80 V. The dark electrical resistivity and Hall effect measurements indicated the n ‐type conduction with an electrical resistivity, electron density and Hall mobility of 2.49×103 Ω cm, 4.76×1012 cm–3 and 527 cm2V–1s–1, respectively. The photosensitivity measurements on the crystal revealed that, the variation of photocurrent with illumination intensity is linear, indicating the domination of monomolecular recombination at room temperature. Moreover, the spectral distribution of the photocurrent allowed the determination of the energy band gap of the crystal studied as 0.88 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
19.
An-Hui Cai Hua Chen Wei-Ke An Jing-Ying Tan Yong Zhou Ye Pan Guo-Xiong Sun 《Journal of Non》2008,354(15-16):1808-1816
A new melting enthalpy ΔHm criterion for the prediction of glass forming ability (GFA) of alloys is proposed and five Zr–Al–Ni–Cu bulk metallic glasses (BMG) with critical dimension Zmax up to ? 7.5 mm are also developed by us in the light of the optimum ΔHm of Zr–Al–Ni–Cu alloy system. And then, we researched the relationships between ΔHm and two GFA parameters (critical cooling rate Rc and Zmax) of five bulk metallic glass (BMG) systems, such as Mg–Ni–Nd, Pd–Cu–Si, La–Al–Ni–Cu, Zr–Al–Ni–Cu and Zr–Ti–Ni–Cu–Be, respectively. The results show that the relationships between ΔHm and Rc are all concave upward parabolas, and the optimum ΔHms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.3960 kJ mol?1, 21.2202 kJ mol?1, 19.7146 kJ mol?1, 18.1455 kJ mol?1 and 13.1558 kJ mol?1, respectively. On the contrary, the relationships between ΔHm and Zmax are all concave downward parabolas, and the optimum ΔHms for Mg–Ni–Nd, Pd–Cu–Si, Zr–Al–Ni–Cu, Zr–Ti–Ni–Cu–Be and La–Al–Ni–Cu are 10.5530 kJ mol?1, 21.0830 kJ mol?1, 19.6603 kJ mol?1, 19.7231 kJ mol?1 and 13.1173 kJ mol?1, respectively. Furthermore, other BMGs’ Rcs or Zmaxs predicted by above-mentioned relationships satisfactorily agree with the tested results, which indicates that these relationships are reliable. However, the predicted results are reliable only if the main components are similar with the fitted BMGs or the additive is sparkle enough that the alloy’s character does not change. On the whole, the ΔHm can act as a criterion for quickly predicting the alloy’s GFA and be helpful for the development of new BMGs. 相似文献
20.
H. Neumann 《Crystal Research and Technology》1990,25(6):667-675
The frequencies of the wurtzite-like modes due to Li–O and Ga–O bond vibrations in LiGaO2 and of the rocksalt-like mode due to Li–O bond vibrations in LiInO2 are determined from the infrared reflectivity spectra of the compounds. The force constants for the Li–O and Ga–O bonds in LiGaO2 follow the same trends as those found for the AIBIIIC2VI chalcogenides with tetrahedral cordination. The results for LiInO2 are compared with measurements on the octahedrally coordinated modification of LiAlO2. 相似文献