Photoluminescence and thermoluminescence properties of Sr3Al2O6:Tb

Photoluminescence and thermoluminescence characteristics of the SrO-Al₂O₃ system doped with terbium have been studied and reported here. The phosphor was synthesized by a reflux sol-gel technique. With a view to study the dosimetric properties, the effect of beta irradiation has been studied in detail; further, concentration quenching effects observed in the emission of various terbium doped phosphors have led to optimization of dopant content. A case is made to project the phosphor as an efficient green light emitting material with good dosimetric properties.     

Synthesis and spectroscopic properties of (C2FxBr0.01 · yCH3CN)n (0.5 < x < 1.0) intercalation compounds

(C₂F _x Br_0.01 · yCH₃CN) _n intercalation compounds, with (C₂F _x Br_0.01) _n (0.5 < x < 1.0) as a host and CH₃CN as a guest (x and y are stoichiometric coefficients), have been synthesized. The influence of fluorine content on the spectroscopic characteristics of the intercalation compounds with acetonitrile has been studied by Raman, IR, and X-ray photoelectron spectroscopies. The macroscopic properties of the intercalation compounds are shown to correlate with their spectroscopic characteristics. The data for the compounds stored in air for about a year indicate that their surface and interior differ in structure.     

Thermal expansion of Bi2.2Sr1.8CaCu2Ox superconductor single crystals

Using a low-temperature stage X-ray diffractometer, we have investigated the temperature dependence of the lattice parameters of single crystal superconductors Bi₂Sr_1.8CaCu₂O_x. The experimental results show that (i) the lattice constants increase linearly with increasing temperature above about 100 K; (ii) thec-axis lattice parameter shows a kink in the superconducting transition region, while thea, b-axis parameters do not show any anomalous behavior in this region; (iii) botha, b, andc show negative thermal expansion coefficients below 40–50 K, which may be related to the characteristics of the Cu-O bond.     

Microstructures and Dielectric Properties of Ba1-xSrxTiO3 Ceramics Doped with B2O3-Li2O Glasses for LTCC Technology Applications

Ba1-xSrxTiO3 ceramics, doped with B2O3-Li2O glasses have been fabricated via a traditional ceramic process at a low sintering temperature of 900 ℃ using liquid-phase sintering aids. The microstructures and di- electric properties of B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have been investigated systemat- ically. The temperature dependence dielectric constant and loss reveals that B2O3-Li2O glasses doped Ba1-xSrxTiO3 ceramics have di?usion phase transformation characteristics. For 5 wt% B2O3-Li2O glasses doped Ba0.55Sr0.45TiO3 composites, the tunability is 15.4% under a dc-applied electric field of 30 kV/cm at 10 kHz; the dielectric loss can be controlled about 0.0025; and the Q value is 286. These composite ceramics sintered at low temperature with suitable dielectric constant, low dielectric loss, relatively high tunability and high Q value are promising candidates for multilayer low-temperature co-fired ceramics (LTCC) and potential microwave tunable devices applications.     

Single step synthesis of Ce doped CaAl2O4 and CaAl4O7 systems

Both CaAl₂O₄ (CA2) and CaAl₄O₇ (CA4) oxide-systems possess monoclinic crystal structure. Herein, we have prepared CA2 and CA4 systems via single step combustion route. A good correlation is observed between calculated and the standard lattice parameters. Ce³⁺ ions were deliberately doped as extrinsic impurities in order to understand the crystal symmetry effects on the emission characteristics in the as-prepared matrices. Large red-shift was observed in CA4-emission spectrum despite of their same crystal structures. Possible reasons are discussed.     

Microwave dielectric properties of Mg4Al2Ti9O25 ceramics

Phase-singular Mg₄Al₂Ti₉O₂₅ ceramics with the pseudobrookite structure suitable for microwave devices such as antenna substrate have been prepared by gel-carbonate method with the dielectric permittivity of 24.7 (at 2-8 GHz), Q-values > 30,000 and temperature coefficients in permittivity (TCK) of less than + 17 ppm K^− 1. The dielectric characteristics are accountable in terms of ordering in the cation sub-lattice.     

RuO2-TiO2/Ti阳极的研究进展

钌系涂层钛阳极具有稳定性好、电催化活性高、环境友好等特点,在电解水、阴极保护以及电化学除垢等领域具有广泛的应用前景。其中,涂层中二氧化钌(RuO₂)的比例与存在形态是决定其电催化活性和稳定性的关键。在涂层钛阳极的制备中,热分解法因其操作简单、成本低、易工业化生产等优势而被广泛使用。介绍了目前在电解行业广泛应用的钌系涂层钛阳极——RuO₂-TiO₂/Ti阳极的应用领域,简述了RuO₂-TiO₂/Ti阳极中钌钛氧化物的特点和作用,并对RuO₂-TiO₂/Ti阳极的失效原因和制备工艺进行了阐述。主要综述了前处理、涂液组分比例、涂液浓度和烧结温度等工艺参数对通过热分解法制备的钛电极稳定性和电催化活性的影响,以及针对RuO₂-TiO₂/Ti阳极的失效原因提出钛阳极未来的改进方向,旨在促进本领域研究者更深入地了解钌钛阳极的特点、失效原因以及如何制备性能优良的涂层钛电极。     

Studies of glass structure in the TeO2  Fe2O3 system

Some structure characteristics of glasses in the TeO₂Fe₂O₃ system have been studied by means of Moessbauer and IR spectroscopy and positron annihilation. Discussion is been made about the character of the chemical bonds and structuring of the glasses on the basis of the experimental data obtained.     

Spectroscopic analysis and the effects of color centers on the laser performance of Nd: CaZn2Y2Ge3O12

Spectroscopic and EPR investigations of Nd³⁺-doped CaZn₂Y₂Ge₃O₁₂ (CAZGAR) have been performed. The absorption, fluorescence, excitation spectra and fluorescence lifetime have been measured at room temperature. The Judd-Ofelt theory has been applied to the measured optical absorption intensities to predict the radiative decay rates, branching ratios, and peak stimulated emission cross section from the metastable ⁴F_3/2 state to the ⁴I_9/2 manifold. The fluorescence lifetime of the ⁴F_3/2 level of Nd³⁺ at low concentration in this host was measured to be 285 ± 10 μs, which is longer than that for Nd³⁺: YAG. Color centers located at zinc octahedral sites have been produced in these crystals by ultraviolet irradiation and have been detected by EPR techniques. The effects of the color centers on the potential laser characteristics of this materials are discussed.     

Highly stable nonlinear behavior against impulse current of ZnO-Pr6O11-CoO-Cr2O3-Y2O3 varistors

The nonlinear electrical behavior against the impulse stress (400-1200 A) in the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃ varistors has been investigated with sintering time. The sintering time did have a significant effect on the clamp ratio, which exhibits a surge protection capability. The varistors sintered for 1 h exhibited the best clamp characteristics, in which the clamp voltage ratio was in the range of K = 1.61-1.92 at a lower impulse current region (5-50 A) and was in the range of K = 2.06-2.55 at a higher single impulse current region (400-1200 A). The best electrical stability against the multi-impulse aging stress of 1200 A was also obtained from the varistors sintered for 2 h, where %ΔE_{1 mA} =−1.6%, %Δα =1.3%, and %ΔJ_L =−4.9%.     

Functional possibilities of Ag- N 0AlGaAs- n +GaAs- n 0GaInAs-au structures with an isotype base region

We have considered the spectral characteristics of two-base structures with isotype heterojunctions and with Schottky and Mott barriers to the base regions and explained the features of the impurity and photovoltaic effects in two-base structures containing deep impurity levels of oxygen and intrinsic defects. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 5, pp. 1005–1009, September–October, 2008.     

A comparison between V2O5 and WO3 thin films as sensitive elements for NO detection

Vanadium oxide (V₂O₅) and tungsten oxide (WO₃) thin films were investigated with the aim to obtain information about their physical and gas sensing properties. The analysis in the presence of different NO concentrations have shown that both materials are able to detect nitrogen oxide, but their responses exhibit different characteristics. In particular, tungsten oxide was found to be more suitable to be used in the field of application for detecting low concentrations. In addition, a mechanism of detection has been considered.     

Commutations dans des couches très minces de Te43Se50Sn7

By thermal deposition in vacuum of very thin films (thickness between 1500 and 8000 Å) of the amorphous semiconductor Te₄₃Se₅₀Sn₇ on a metallic counterelectrode (Au, Cr) we have prepared MSM structures. The top contact was made by means of a tungsten alloy needle. The I–V characteristics and the observed switching effects are discussed on the hypothesis of a purely electronic model. The forming processes depend on the deposition conditions of the semiconductor film; they are described in detail. The thermal dependence of these processes is obvious in all cases.     

Pinning potential transport measurements of Bi2Sr2CaCu2Ox thin films

Flux creep characteristics ofc-axis-oriented Bi₂Sr₂CaCu₂O _x thin films grown by the method of electron beam evaporation of stoichiometric target and subsequent annealing have been investigated in the absence of external magnetic field. A decrease of the pinning potential with decreasing temperature is obtained fromI–V curves. This result is explained by the presence of the spatially nonlinear pinning potential.     

Luminescence quenching by manganese ions in MO–CaF2–B2O3 glasses

Thermoluminescence (TL) characteristics of X-ray irradiated calcium fluoro borate glasses mixed with three different alkali oxide modifiers viz., Li₂O, Na₂O and K₂O have been studied in the temperature range 303–600 K; all the glasses have exhibited single TL peak at 485, 541 and 497 K respectively. The glasses containing Na₂O as modifier has exhibited the maximum TL light output. The doping of manganese oxide by a small concentration (0.2 mol%) in all these glasses has been observed to inhibit TL light output drastically with shifting of peak positions towards lower temperatures. The trap depth parameters associated with the observed TL peaks have been evaluated using Chen’s formulae. The probable mechanism responsible for quenching of TL emission by manganese ions in these glasses has been suggested with the aid of optical absorption, IR spectra and differential scanning calorimetric studies.     

Formation and properties of glasses in the CaF2AlF3P2O5 system

Glasses from the system CaF₂AlF₃P₂O₅ have been synthesized. Glass formation characteristics, thermal expansion, and optical transmission of these glasses in the visible and infrared regions are described. Incorporation of P₂O₅ in the system greatly suppressed the spontaneous crystallization tendencies of the CaF₂AlF₃ binary system. The glasses obtained from the system transmit in the mid-infrared range. A strong absorption band centerd at 4.8 microns is a characteristic of these glasses. The absorption band is related to the presence of P₂O₅ in the glass.     

Comparison of hydrogen storage characteristics between as-cast and melt-spun TiCr1.1V0.5Fe0.1Mn0.1 alloys

Hydrogen storage characteristics of as-cast and melt-spun TiCr_1.1V_0.5Fe_0.1Mn_0.1 alloys were investigated by pressure–composition–temperature (PCT) tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD showed that both the as-cast and the melt-spun alloys were similarly consisted of V based BCC phase and Ti_1.07Cr_1.93 phase. However, PCT tests showed that the melt-spun alloy, with larger hysteresis between hydrogen absorption and desorption, had higher hydrogen storage capacity than the as-cast alloy. More interestingly, the phase compositions of the two fully hydrogenated alloys were entirely different. The as-cast and the melt-spun alloys should have different atomic motion mechanisms during the course of hydrogenation.     

Dielectric properties of Ba0.6Sr0.4TiO3-Sr(Ga0.5Ta0.5)O3 solid solutions

Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ solid solutions are prepared by a solid-state reaction method, and their dielectric and tunable characteristics are investigated. The solid solutions with cubic perovskite structures are obtained for compositions of 10-50 mol% Sr(Ga_0.5Ta_0.5)O₃. It is observed that the addition of Sr(Ga_0.5Ta_0.5)O₃ into Ba_0.6Sr,sub>0.4TiO₃ causes a shift in the phase transition peak to a lower temperature. Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ solid solutions exhibit depressed and broadened phase transition peaks, resulting in decreased dielectric constants and dielectric losses at room temperature. With the increase of Sr(Ga_0.5Ta_0.5)O₃ content, the dielectric constant, loss tangent, and tunability are decreased. 0.9Ba_0.6Sr_0.4TiO₃-0.1Sr(Ga_0.5Ta,sub>0.5)O₃ has a dielectric constant ϵ = 534 and a tunability of 16% at 100 kHz under 2.63 kV/mm. The dielectric characteristics of Ba_0.6Sr_0.4TiO₃-Sr(Ga_0.5Ta,sub>0.5)O₃ ceramics at microwave frequencies are also evaluated.     

Josephson effects in Nb3Sn microbridges

We have studied Josephson effects in long narrow Nb3Sn microbridges at temperatures up to 17 K. These microbridges are formed by photolithographic techniques and subsequently subjected to controlled electrical discharges to modify the intrinsic Tcof the bridge region. The bridges exhibit 10 GHz micro wave steps in their I-V characteristics whose amplitudes are in excellent agreement with the Resistively Shunted Junction (RSJ) model. I-V characteristics (with and without microwaves) can be fit assuming an effective temperature approximately 15 K above the bath temperature. We have also investigated in detail structures in the I-V characteristics in the absence of microwaves. We show experimentally that phase-slip centers are induced at weak superconducting positions along the bridge when the S-N boundary of an expanding hot spot reaches within a thermal healing distance. The critical current of the phase-slip center thus formed exhibits a temperature dependence (1-T/Tc)^1/2instead of the usual mean field result (1-T/Tc)^3/2.     

Photoelectrochimie de CdIn2S4: Caracteristiques photoelectrochimiques de CdIn2S4(n)electrolyte aqueux

The photoelectrochemical characteristics of the $\text{CdIn}{}_2\text{S}{}_4\text{(n)}\text{electrolyte}$ cell have been studied. Surface traitments enhance the short circuit current density. This phenomena has been interpreted by a decrease of the recombination of minority carriers at the electrode/electrolyte interface. The variation of open-circuit voltage up on the incident light intensity shows that the cell can be represented by the Schottky barrier model.