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1.
Intense red phosphors, AgGd1−xEux(W1−yMoy)2O8 (x=0.0-1.0, y=0.0-1.0), have been synthesized through traditional solid-state reaction and characterized by X-ray diffraction (XRD) and photoluminescence (PL). XRD results reveal that AgGd1−xEuxW2O8 synthesized at 1000 °C has a tetragonal crystal structure, which is named as high temperature phase (HTP) AgGdW2O8. All phosphors compositions with Eu3+ show red and green emission on excitation either in the charge-transfer or Eu3+ levels. Analysis of the emission spectra with different Eu3+ concentrations reveal that the optimum dopant concentration for Eu3+ is x=0.6 in the HTP AgGd1−xEuxW2O8 (x=0.0-1.0). Studies on the AgGd0.4Eu0.6(W1−yMoy)2O8 (y=0.0-1.0) and AgGd1−xEux(W0.7Mo0.3)2O8 (x=0.0-1.0) show that the emission intensity is maximum for compositions with y=0.3 and x=0.5, respectively, and a decrease in emission intensity is observed for higher y or x values. The Mo6+ and Eu3+ co-doped AgGd(WO4)2 phosphors show higher emission intensity in comparison with the singly Eu3+-doped AgGd(WO4)2 in UV region. The intense emission of the tungstate/molybdate phosphors under 394 and 465 nm excitations, respectively, suggests that these materials are promising candidates as red-emitting phosphors for near-UV/blue GaN-based white LED for white light generation. 相似文献
2.
P.M. Shirage K. Kihou K. Miyazawa C.H. Lee H. Kito Y. Yoshida H. Eisaki Y. Tanaka A. Iyo 《Physica C: Superconductivity and its Applications》2010,470(20):986-988
We report the iron isotope effect on a transition temperature (Tc) in an optimally-doped (Ba,K)Fe2As2 (Tc = 38 K) and SmFeAsO1−y (Tc = 54 K) superconductors. In order to obtain the reliable isotope shift in Tc, twin samples with different iron isotope mass are synthesized in the same conditions (simultaneously) under high-pressure. We have found that (Ba,K)Fe2As2 shows an inverse iron isotope effect αFe = −0.18 ± 0.03 while SmFeAsO1−y shows a small iron isotope effect αFe = −0.02 ± 0.01, where the isotope exponent α is defined by Tc ∼ M−α (M is the isotopic mass). The results show that αFe changes in the iron-based superconductors depending on the system. The distinct iron isotope effects imply the exotic coupling mechanism in the iron-based superconductors. 相似文献
3.
Luminescent properties of KGd1−x(WO4)2:Eux and KGd1−x(WO4)2−y(MoO4)y:Eux phosphors in UV-VUV regions
KGd1−x(WO4)2−y(MoO4)y:Eu3+x(0.1?x?0.75, y=0 and 0.2) phosphors are synthesized through traditional solid-state reaction and their luminescent properties in ultraviolet (UV) and vacuum ultraviolet (VUV) regions are investigated. Under 147 nm excitation, these phosphors show characteristic red emission with good color purity. In order to improve their emission intensity, the MoO42− (20 wt%) is introduced into the anion of KGd1−x(WO4):Eu3+x. The Mo6+ and Eu3+ co-doped KGd(WO4)2 phosphors show higher emission intensity in comparison with the singly Eu3+-doped KGd(WO4)2 in VUV region. The chromaticity coordination of KGd0.45(WO4):Eu3+0.55 is (x=0.669, y=0.331), while that of KGd0.45(WO4)1.8(MoO4)0.2:Eu3+0.55 is (x=0.666, y=0.334) in VUV region. 相似文献
4.
Samples of Ni1−yZnyCu0.3Fe1.7O4; 0.0?y?0.6 were prepared by the solid state reaction method. X-ray investigations were carried out in order to assure the formation of the samples in single spinel phase. The analysis of X-ray data shows that the unit cell parameter increases with increasing Zn concentration and ascribed to the variation of the predicted cation distribution. Seebeck coefficient measurements were performed to know the type of charge carriers participating in the conduction mechanism. The magnetic susceptibility for the prepared samples was measured using Faraday’s method at different temperatures as a function of the magnetic field intensity. The magnetic parameters were calculated from the magnetic susceptibility data, in the temperature range (300–800 K) at three different magnetic field intensities of (1280, 1733 and 2160 Oe). The effective magnetic moment (μeff) showed that, the critical Zn content was y=0.2. 相似文献
5.
Ca0.54Sr0.34−1.5xEu0.08Smx(MoO4)y (WO4)1−y red phosphors were prepared by solid-state reaction using Na+ as a charge compensator for light-emitting diodes (LED). The effects of Na+ concentration, synthesis temperature, reaction time and Eu3+ concentration were studied for the properties of luminescence and crystal structure of red phosphors. The results show that the optimum reaction condition is 6%, 900 °C, 2 h and 8%. The photoluminescence spectra show that red phosphors are effectively excited at 616 nm by 292, 395 and 465 nm. The wavelengths of 465 nm nicely match the widely applied emission wavelengths of blue LED chips. 相似文献
6.
The structural parameters with stability upon Si incorporation and elastic, electronic, thermodynamic and optical properties of Ti3Al1−xSixC2 (0≤x≤1) are investigated systematically by the plane wave pseudopotential method based on the density functional theory (DFT). The increase of some elastic parameters with increasing Si-content renders the alloys to possess higher compressive and tensile strength. The Vickers hardness value obtained with the help of Mulliken population analysis increases as x is increased from 0 to 1. The solid solutions considered are all metallic with valence and conduction bands, which have a mainly Ti 3d character, crossing the Fermi level. The temperature and pressure dependences of bulk modulus, normalized volume, specific heats, thermal expansion coefficient, and Debye temperature are all obtained through the quasi-harmonic Debye model with phononic effects for T=0−1000 K and P=0−50 GPa. The obtained results are compared with other results available. Further an analysis of optical functions for two polarization vectors reveals that the reflectivity is high in the visible–ultraviolet region up to ∼10.5 eV region showing promise as a good coating material. 相似文献
7.
In this paper, TaxC1−x coatings were deposited on 316L stainless steel (316L SS) by radio-frequency (RF) magnetron sputtering at various substrate temperatures (Ts) in order to improve its corrosion resistance and hemocompatibility. XRD results indicated that Ts could significantly change the microstructure of TaxC1−x coatings. When Ts was <150 °C, the TaxC1−x coatings were in amorphous condition, whereas when Ts was ≥150 °C, TaC phase was formed, exhibiting in the form of particulates with the crystallite sizes of about 15-25 nm (Ts = 300 °C). Atomic force microscope (AFM) results showed that with the increase of Ts, the root-mean-square (RMS) values of the TaxC1−x coatings decreased. The nano-indentation experiments indicated that the TaxC1−x coating deposited at 300 °C had a higher hardness and modulus. The scratch test results demonstrated that TaxC1−x coatings deposited above 150 °C exhibited good adhesion performance. Tribology tests results demonstrated that TaxC1−x coatings exhibited excellent wear resistance. The results of potentiodynamic polarization showed that the corrosion resistance of the 316L SS was improved significantly because of the deposited TaxC1−x coatings. The platelet adhesion test results indicated that the TaxC1−x coatings deposited at Ts of 150 °C and 300 °C possessed better hemocompatibility than the coating deposited at Ts of 25 °C. Additionally, the hemocompatibility of the TaxC1−x coating on the 316L SS was found to be influenced by its surface roughness, hydrophilicity and the surface energy. 相似文献
8.
Bhoj Raj Gautam Igor Dubenko Arjun Kumar Pathak Shane Stadler Naushad Ali 《Journal of magnetism and magnetic materials》2009,321(1):29-33
The influence of the substitution of manganese by boron on the crystal structure and magnetic properties of Ni2Mn1−xBxGa Heusler alloys with 0?x?0.5 has been investigated using X-ray diffraction, thermal expansion, resistivity, and magnetization measurements. The samples with concentrations x<0.25 were found to be of single phase and belonged to the cubic L21 crystal structure at room temperature. Crystal cell parameters of the alloys decreased from 5.830 to 5.825 Å with increasing boron concentration (x) from 0 to 0.25. The alloys were ferromagnetically ordered at 5 K and the saturation magnetization decreased with increasing boron concentration. The ferromagnetic ordering and structural transition temperatures for 0?x?0.3 have been observed and the phase (x−T) diagram of the Ni2Mn1−xBxGa system was constructed. The phase (x−T) diagram indicates that the ground state of Ni2Mn1−xBxGa alloys belongs to ferromagnetic martensitic, premartensitic, and austenitic phases in x?0.12, 0.12<x?0.18, and 0.18<x?0.3, respectively. The relative influence of cell parameters and electron concentrations on the phase diagram is discussed. 相似文献
9.
In this work, we report on the physical properties of good-quality polycrystalline superconducting samples of La2−xSrxCu1−yZnyO4−δ (y=0, 0.02) prepared by a wet-chemical method, focusing on the temperature dependence of the critical current. Using the wet-chemical method, we were able to produce samples with improved homogeneity compared to the solid-state method. A complete set of samples with several carrier concentrations, ranging from the underdoped (strontium concentration x≈0.05) to the highly overdoped (x≈0.25) region, were prepared and investigated. The X-ray diffraction analysis, zero-field cooling magnetization and electrical resistivity measurements were reported on earlier. The structural parameters of the prepared samples seem to be slightly modified by the preparation method and their critical temperatures were lower than reported in the literature. The temperature dependence of the critical current was explained by a theoretical model which took the granular structure of the samples into account. 相似文献
10.
Feihui Li 《Applied Surface Science》2009,255(7):4225-4231
The electrochemical behaviors of BiIII, TeIV and SbIII single ions and their mixtures were investigated in nitric acid and hydrochloric acid system separately. Based on which, BixSb2−xTey thermoelectric films were prepared by potentiostatic electrodeposition from the solutions with different concentrations of BiIII, TeIV and SbIII in the two acid systems. The morphologies, compositions, structures, Seebeck coefficients and resistivities of the deposited thin films were characterized and compared by ESEM (or FESEM), EDS, XRD, Seebeck coefficient measurement system and four-probe resistivity measuring device respectively. The results show that although BixSb2−xTey thermoelectric thin film which structure is consistent with the standard pattern of Bi0.5Sb1.5Te3 can be gained in both of the two acid solutions by adjusting the deposition potential, their morphologies and thermoelectric properties have big differences in different acid solutions. 相似文献
11.
Tanjore V. Jayaraman Mark A. KotenJeffrey E. Shield 《Journal of magnetism and magnetic materials》2011,323(15):2037-2041
The magnetocaloric properties of melt-spun Gd-B alloys were examined with the aim to explore their potential application as magnetic refrigerants near room temperature. A series of Gd100−xBx (x=0, 5, 10, 15, and 20 at%) alloys were prepared by melt spinning. With the decrease in Gd/B ratio, Curie temperature (TC) remains constant at ∼293 K, and saturation magnetization, at 275 K, decreases from ∼100 to ∼78 emu/g. Negligible magnetic hysteresis was observed in these alloys. The peak value of magnetic entropy change, (−ΔSM)max, decreased from ∼9.9 J/kg K (0-5 T) and ∼5.5 J/kg K (0-2 T) for melt-spun Gd to ∼7.7 J/kg K (0-5 T) and ∼4.0 J/kg K (0-2 T), respectively for melt-spun Gd85B15 and Gd80B20 alloys. Similarly, the refrigeration capacity (q) decreased monotonously from ∼430 J/kg (0-5 T) for melt-spun Gd to ∼330 J/kg (0-5 T) for melt-spun Gd80B20 alloy. The near room temperature magnetocaloric properties of melt-spun Gd100−xBx (0≤x≤20) alloys were found to be comparable to few first-order transition based magnetic refrigerants. 相似文献
12.
Y. Zhang C.H. Cheng Y.L. Chen Y.J. Cui W.G. You H. Zhang Y. Zhao 《Physica C: Superconductivity and its Applications》2010,470(20):1073-1076
The electronic structures of Fe-based superconductor SmFeAsO1−xFx and SmFe1−yIryAsO are compared through X-ray photoemission spectroscopy in this study. With fluorine or iridium doping, the electronic structure and chemical environment of the SmFeAsO system were changed. The fluorine was doped at an oxygen site which introduced electrons to a reservoir Sm–O layer. The iridium was doped at an Fe site which introduced electrons to a conduction Fe–As layer directly. In a parent material SmFeAsO, the magnetic ordering corresponding to Fe3d in the low-spin state is suppressed by both fluorine and iridium doping through suppressing the magnetism of 3d itinerant electrons. Compared to fluorine doping, iridium doping affected superconductivity more significantly due to an iridium-induced disorder in FeAs layers. 相似文献
13.
The effects of 60Co (γ-ray) irradiation on the electrical and dielectric properties of Al-TiW-Pd2Si/n-Si Schottky diodes (SDs) have been investigated by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and 500 KHz. The corrected capacitance and conductance values were obtained by eliminating the effect of series resistance (Rs) on the measured capacitance (Cm) and conductance (Gm) values. The high-low frequency capacitance (CHF-CLF) method given in [12] as Nss = (1/qA) [((1/CLF) − (1/Cox))−1 − ((1/CHF) − (1/Cox))−1] was successfully adapted to the before-after irradiation capacitance given in this report as Nss = (1/qA) [((1/Cbef) − (1/Cox))−1 − ((1/Cafter) − (1/Cox))−1] for the analyzing the density of interface states. The Nss-V plots give a distinct peak corresponding to localized interface states regions at metal and semiconductor interface. The experimental values of the ac electrical conductivity (σac), the real (M′) and imaginary (M″) parts of the electrical modulus were found to be strong functions of radiation and applied bias voltage, especially in the depletion and accumulation regions. The changes in the dielectric properties in the depletion and accumulation regions stem especially from the restructuring and reordering of the charges at interface states and surface polarization whereas those in the accumulation region are caused by series resistance effect. 相似文献
14.
Zujian Wang 《Solid State Communications》2011,151(4):329-331
The relaxor behavior was revealed in the solid solution (1−x)BaSnO3-xPbTiO3[(1−x)BSn-xPT] with compositions near x=0.50. The real permittivity (ε′) and loss tangent (tanδ) exhibit diffuse and dispersive maxima, whose temperature shifts towards a higher temperature upon the increasing frequency. The frequency dependence of the temperature of the dielectric maximum (Tm) follows the Vogel-Fulcher law, as in the canonical relaxor. A deviation from the Curie-Weiss law was observed below the Burns temperature (TB) and well above the Curie temperature (TC). These phenomena are well consistent with typical relaxors, which explains the existence of the relaxor behavior in the (1−x)BSn-xPT solid solution. 相似文献
15.
H. Yurtseven F. Eraslan 《Journal of Quantitative Spectroscopy & Radiative Transfer》2006,102(3):513-518
We study here the Pippard relations modified spectroscopically for the NH4Cl crystal. By relating the specific heat CP to the frequency shift (1/ν)(∂ν/∂T)P for the disorder-allowed Raman modes of ν7 (93 cm−1) and ν5 (144 cm−1) in NH4Cl close to the tricritical point (P=1.6 kbar, TC=257 K), we show that the first Pippard relation is valid for this crystalline system. 相似文献
16.
Hf1−xSixOy is an attractive candidate material for high-k dielectrics. We report in this work the deposition of ultra-thin Hf1−xSixOy films (0.1 ≤ x ≥ 0.6) on silicon substrate at 450 °C by UV-photo-induced chemical vapour deposition (UV-CVD) using 222 nm excimer lamps. Silicon(IV) and hafnium(IV) organic compounds were used as the precursors. Films from around 5 to 40 nm in thickness with refractive indices from 1.782 to 1.870 were grown. The deposition rate was found to be of 6 nm/min at a temperature of 450 °C. The physical, interfacial and electrical properties of hafnium silicate (Hf1−xSixOy) thin films were investigated by using X-ray photoelectron spectroscopy, ellipsometry, FT-IR, C-V and I-V measurements. XRD showed that they were basically amorphous, while Fourier transform infrared spectroscopy (FT-IR), clearly revealed Hf-O-Si absorption in the photo-CVD deposited Hf1−xSixOy films. Surface and interfacial properties were analysed by TEM and XPS. It is found that carbon content in the films deposited by UV-CVD is very low and it also decreases with increasing Si/(Si + Hf) ratio, as low as about 1 at.% at the Si/(Si + Hf) ratio of 60 at.%. 相似文献
17.
The CrNxOyCz coatings were deposited by planar DC reactive magnetron sputtering onto AZ31 Mg alloy and high speed tool steel (HSTS) substrates at a substrate temperature of 200 °C. The effect of N2 content on composition and structure of the CrNxOyCz coatings was investigated. The structure of the CrNxOyCz coatings was analyzed by a glancing angle X-ray diffraction (GXRD). The cross-section morphology and thickness of the CrNxOyCz coatings were checked by a field emission scanning electron microscope (FESEM), and the composition profile and chemical state were carried out by an X-ray photoelectron spectroscopy (XPS). The experimental results showed that the structure and phase composition of the CrNxOyCz coatings depended on N2 content. The evolution of the structure of CrNxOyCz coatings was consistent with CrNx-based coatings, and the CrNxOyCz coatings contained Cr2O3, CrO2, CrO, Cr3C2, CrNx (Cr, CrN, Cr2N), as well as different chromium oxynitride. However, the carbide and oxynitride were oxidized after annealing. 相似文献
18.
The samples of Cu1−xPtxFeO2 (0 ≤ x ≤ 0.05) delafossite have been synthesized by solid-state reaction method to investigate their optical and electrical properties. The properties of electrical resistivity and Seebeck coefficient were measured in the high temperature ranging from 300 to 960 K, and the Hall effect and the optical properties were measured at room temperature. The obtained results of Seebeck showed the samples are p-type conductor. The optical properties at room temperature exhibited the samples are transparent visible light material with optical direct gap 3.45 eV. The low electrical resistivity, hole mobility and carrier density at room temperature displayed value ranging from 0.29 to 0.08 Ω cm, 1.8 to 8.6 cm2/V s and 1.56 × 1018 to 4.04 × 1019 cm−3, respectively. The temperature range for transparent visible light is below 820 K because the direct energy gap contains value above 3.1 eV. Consequently, the Cu1−xPtxFeO2 delafossite enhance performance for materials of p-type transparent conducting oxide (TCO) with low electrical resistivity. 相似文献
19.
Shucheng Xu 《Proceedings of the Combustion Institute》2007,31(1):159-166
Kinetics and mechanisms for reactions of OH with methanol and ethanol have been investigated at the CCSD(T)/6-311 + G(3df, 2p)//MP2/6-311 + G(3df, 2p) level of theory. The total and individual rate constants, and product branching ratios for the reactions have been computed in the temperature range 200-3000 K with variational transition state theory by including the effects of multiple reflections above the wells of their pre-reaction complexes, quantum-mechanical tunneling and hindered internal rotations. The predicted results can be represented by the expressions k1 = 4.65 × 10−20 × T2.68 exp(414/T) and k2 = 9.11 × 10−20 × T2.58 exp(748/T) cm3 molecule−1 s−1 for the CH3OH and C2H5OH reactions, respectively. These results are in reasonable agreements with available experimental data except that of OH + C2H5OH in the high temperature range. The former reaction produces 96-89% of the H2O + CH2OH products, whereas the latter process produces 98-70% of H2O + CH3CHOH and 2-21% of the H2O + CH2CH2OH products in the temperature range computed (200-3000 K). 相似文献
20.
Carlo Cavallotti Marco Derudi Renato Rota 《Proceedings of the Combustion Institute》2009,32(1):115-121
The C7H7 potential energy surface was studied from first principles to determine the benzyl radical decomposition mechanism. The investigated high temperature reaction pathway involves 15 accessible energy wells connected by 25 transition states. The analysis of the potential energy surface, performed determining kinetic constants of each elementary reaction using conventional transition state theory, evidenced that the reaction mechanism has as rate determining step the isomerization of the 1,3-cyclopentadiene, 5-vinyl radical to the 2-cyclopentene,5-ethenylidene radical and that the fastest reaction channel is dissociation to fulvenallene and hydrogen. This is in agreement with the literature evidences reporting that benzyl decomposes to hydrogen and a C7H6 species. The benzyl high-pressure decomposition rate constant estimated assuming equilibrium between the rate determining step transition state and benzyl is k1(T) = 1.44 × 1013T0.453exp(−38400/T) s−1, in good agreement with the literature data. As fulvenallene reactivity is mostly unknown, we investigated its reaction with hydrogen, which has been proposed in the literature as a possible decomposition route. The reaction proceeds fast both backward to form again benzyl and, if hydrogen adds to allene, forward toward the decomposition into the cyclopentadienyl radical and acetylene with high-pressure kinetic constants k2(T) = 8.82 × 108T1.20exp(1016/T) and k3(T) = 1.06 × 108T1.35exp(1716/T) cm3/mol/s, respectively. The computed rate constants were then inserted in a detailed kinetic mechanism and used to simulate shock tube literature experiments. 相似文献