共查询到20条相似文献,搜索用时 15 毫秒
1.
B. Denker B. Galagan V. Osiko I. Shulman S. Sverchkov E. Dianov 《Applied physics. B, Lasers and optics》2009,95(4):801-805
A new Bi-doped Mg–Al–silicate glass is suggested and investigated. It can be fabricated by moderate-temperature routine technology.
The characteristic relaxation time of 300–800 μs in combination with the high quantum yield (up to 85%) and wide excitation
spectrum makes this glass a promising laser material. The obtained quadratic dependence of the visible absorption intensity
is an argument in favor of the hypothesis that the absorption and infrared luminescence in Bi-doped glasses are caused by
Bi2 dimers. 相似文献
2.
The effect of donor–acceptor (D-A) substituent and chain length on the electrical polarisabilities and first hyper polarisability of cis and trans biphenyl oligomeric compounds have been investigated using density functional theory-based hybrid functional CAM-B3LYP with 6-311G (2d,2p) basis set. Our extensive computational study reveals that both average polarisability and first hyper polarisability of the studied compounds increase with the increasing ethylene spacer chain length. Again the substitution of donor (NMe2) and acceptor (C≡N) at the para position of the phenyl rings to each oligomer shows order of magnitude increase of both αav and βav value compared to the unsubstituted one. This increased αav and βav values have been explained due to increasing charge transfer contribution resulting from decreasing optical energy gap (ΔE?=?S1???S0) upon D-A substitution. It is also observed that the charge transfer contribution to first hyperpolarisability (βCT) is more than the polarisability (αCT) for the studied molecules. The electronic spatial extent (<R2>) which is a measure of electron density volume around the molecule is found to play a major role along with the intramolecular charge transfer character to explain the non-linear variation of first hyperpolarisability (βav) as a function of ethylene spacer chain length (n) and D-A substitution. 相似文献
3.
Min Ge Zhaorong Yang Li Li Lina Chen Li Pi Zhe Qu Bosen Wang Yuping Sun Yuheng Zhang 《Physica C: Superconductivity and its Applications》2009,469(7-8):297-299
In this paper, sulfur substitution and pressure effect on superconductivity of α-FeSe has been investigated in Fe(Se1 ? xSx)0.88 (x = 0.1, 0.2). For x = 0.1, the critical temperature Tc is slightly larger than that of non-substituted sample, in consistent with the pressure effect on the superconductivity of α-FeSe. However, with further increasing S content to x = 0.2, Tc decreases. Temperature dependent of specific heat showed that the structural transition seems to be suppressed. Tc for x = 0.2 can be further decreased by applying pressure of 5 kbar, in contrary to the pressure effect on α-FeSe. We suggest that, in addition to the suppression of structural transition, other factors like the increase of carrier concentration should be considered for understanding the pressure effect on the superconductivity of α-FeSe. 相似文献
4.
M. Vinodha 《Molecular physics》2018,116(9):1145-1152
The structure–activity relationship of fused π-conjugated imidazolium cation with three counter anion molecules, BF4?, CF3SO3? and (CF3SO2)2N?, was studied using electronic structure calculations. The structural, opto-electronic and charge transport properties of these complexes were studied. The charge transfer from π-conjugated imidazolium(I) to counter anion was confirmed in all the studied complexes. Interaction energy varies significantly depending on the counter anion and the stability was found higher for I-BF4 complex than both I–CF3SO3 and I–(CF3SO2)2N complexes. The strong (C–H)+···F? hydrogen bond of length 1.95 Å between fused π-conjugated imidazolium and BF?4 anion is the driving force for the strongest interaction energy in I–BF4 complex. The energy decomposition analysis confirms that the interaction between imidazolium and counter anion is mainly driven by electrostatic and orbital interaction. It has been observed that the absorption spectra of the complex are independent of anion nature but the influence of anion character is observed on frontier molecular orbital pattern. The charge transport property of I–BF4 complex was studied by using tight-binding Hamiltonian approach and found that the hole mobility in I–BF4 is 1.13 × 10?4 cm2 V?1 s?1. 相似文献
5.
M. M. Musakhanov 《Czechoslovak Journal of Physics》1982,32(3):248-251
The effective Hamiltonian for theN system is proposed in the framework of the Chiral Bag Model (CBM). The taking into account of gluonic and pionic correctinos to the pion-nucleon coupling constantg
N and the-decay axial constantg
A leads tog
N 13·5,g
A 1·28 which are in good agreement with experimental data.Presented at the symposium Mesons and Light Nuclei, Liblice, Czechoslovakia, June 1981.I wish to thank Gulamov K. G., Shelest V. P. and Zinoviev G. M. for useful discussions. 相似文献
6.
Er3+-doped heavy metal borosilicate glasses were prepared using conventional melting and quenching method. The emission spectra of 4I13/2 → 4I15/2 transition were observed upon excitation at 974 nm and the lifetime of 4I13/2 level of Er3+ was measured. Based on these data, the fluorescence properties of Er3+ are investigated on the emission and gain characteristics at the 1.5 μm bands. In particular, the effect of relative heavy metal content on fluorescence properties is discussed. 相似文献
7.
《Composite Interfaces》2013,20(7-9):829-839
Composites were fabricated with alkali (10%, 15% and 20%) treated bamboo fibers incorporated to the extent of 50% (by volume) and polyester resin. Impact test was made on bamboo strips and composites samples. It was observed that the fracture energy undergoes an increase from untreated to alkali treated bamboo strips. Alkali treated bamboo fiber composites show higher fracture energy value than the untreated bamboo fiber composites. The phenomenal change was quite evident from scanning electron micrographs of the fractured surface. Considering the effects of all factors, the work of fracture shows maximum value in the case of 20% alkali treated bamboo strip composites. It was also observed that the rate of increase of work of fracture value is much higher in the case of composite samples than the bamboo sample. It was explained on the basis of synergism obtained by improved interfacial adhesion between fiber and matrix, and removal of hemicellulose from the bamboo itself, which was evident from the intermolecular H-bonding formation studied by FT-IR. 相似文献
8.
Xiangqian Shen Mingquan Liu Fuzhan Song Yongwei Zhu 《Applied Physics A: Materials Science & Processing》2011,104(1):109-116
Sr1−x
La
x
Zn
x
Fe12−x
O19/poly(vinylpyrrolidone) (PVP) (0.0≤x≤0.5) precursor nanofibers were prepared by the sol–gel assisted electrospinning method from starting reagents of metal salts
and PVP. Subsequently, the Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers with diameters of around 100 nm were obtained by calcination of the precursor at 800 to 1000°C for 2 h. The precursor
and resultant Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers were characterized by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectrometer and
vibrating sample magnetometer. The grain sizes of Sr0.8La0.2Zn0.2Fe11.8O19 nanofibers are in a nanoscale from 40 to 48 nm corresponding to the calcination temperature from 800 to 1000°C. With La–Zn
substitution content increase from 0 to 0.5, the grain size and lattice constants for the Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers obtained at 900°C show a steady reduction trend. With variations of the ferrite particle size arising from the
La–Zn substitution, the nanofiber morphology changes from the necklace-like structure linking by single elongated plate-like
particles to the structure building of multi-particles on the nanofiber cross-section. The specific saturation magnetization
of Sr1−x
La
x
Zn
x
Fe12−x
O19 nanofibers initially increases with the La–Zn content, reaching a maximum value 72 A m2 kg−1 at x=0.2, and then decreases with a further La–Zn content increase up to x=0.5, while the coercivity exhibits a continuous reduction from 413 (x=0) to 219 kA m−1 (x=0.5). The mechanism for the La–Zn substitution and the nanofiber magnetic property are analyzed. 相似文献
9.
Khalid Mehmood Ur Rehman 《Chinese Journal of Physics (Taipei)》2018,56(2):468-475
We have investigated the influence of Pr–ZnAl substitution on the magnetic and microstructural properties of M-type strontium hexaferrites Sr1.0-xPrxFe12.0-x(Zn0.5Al0.5)xO19 (0.0 ≤ x ≤ 0.5) synthesized by the standard ceramic method. X-ray diffraction (XRD) was carried out to determine the crystal structure and the phase identification of the hexaferrites showed that a single magnetoplumbite phase was exhibited in the hexaferrites with Pr–ZnAl content (x) from 0.0 to 0.4 and impurity phase α-Fe2O3 was observed in the structure when Pr–ZnAl content (x)?=?0.5. The morphology of the hexaferrites was analyzed by a field emission scanning electron microscopy (FE-SEM). The representative FE-SEM micrographs showed that the particles were regular hexagonal platelets and the average grain size basically kept unchanged with increasing Pr–ZnAl content (x). A magnetic property measurement system was used to measure the magnetic properties of the hexaferrites. The remanence (Br), maximum energy product [(BH)max] and Hk/Hcj ratio decreased with increasing Pr–ZnAl content (x) from 0.0 to 0.5. The intrinsic coercivity (Hcj) and magnetic induction coercivity (Hcb) first increased with increasing Pr–ZnAl content (x) from 0.0 to 0.1, and decreased with increasing Pr–ZnAl content (x) from 0.1 to 0.2, and then increased when Pr–ZnAl content (x) ≥ 0.2. 相似文献
10.
《Journal of magnetism and magnetic materials》1999,192(3):490-498
Dilution of the magnetic interactions between Cr3+ ions by Ti3+ ions was observed in the CrS2 layer of the misfit-layer compound ∼LaCrS3. Pure ∼LaCrS3 has complex magnetic properties which are reminiscent of spin glass behavior. This magnetic behavior comes from both the modulated character of the structure and the magnetic frustration of the planar-antiferromagnetic-triangular network of Cr3+ ions. Thus, there is a large hysteresis between the zero field cooled and the field cooled magnetic susceptibility curves below the transition temperature (≈75 K). Formation of a solid solution ∼LaCr1−xTixS3 by the addition of Ti3+ ions results in the decrease of transition temperature up to a doping level of x≈0.5, where the transition is no longer observed. The magnetic behavior of the phase with x≈0.5 is similar to that of several random exchange antiferromagnetic compounds. 相似文献
11.
Igor Dubenko Tapas Samanta Arjun Kumar Pathak Alexandr Kazakov Valerii Prudnikov Shane Stadler Alexander Granovsky Arcady Zhukov Naushad Ali 《Journal of magnetism and magnetic materials》2012
The studies of magnetocaloric properties, phase transitions, and phenomena related to magnetic heterogeneity in the vicinity of the martensitic transition (MT) in Ni–Mn–In and Ni–Mn–Ga off-stoichiometric Heusler alloys are summarized. The crystal structure, magnetocaloric effect (MCE), and magnetotransport properties were studied for the following alloys: Ni50Mn50−xInx, Ni50−xCoxMn35In15, Ni50Mn35−xCoxIn15, Ni50Mn35In14Z (Z=Al, Ge), Ni50Mn35In15−xSix, Ni50−xCoxMn25+yGa25−y, and Ni50–xCoxMn32−yFeyGa18. It was found that the magnetic entropy change, ΔS, associated with the inverse MCE in the vicinity of the temperature of the magneto-structural transition, TM, persists in a range of (125-5) J/(kg K) for a magnetic field change ΔH=5 T. The corresponding temperature varies with composition from 143 to 400 K. The MT in Ni50Mn50−xInx (x=13.5) results in a transition between two paramagnetic states. Associated with the paramagnetic austenite-paramagnetic martensite transition ΔS=24 J/(kg K) was detected for ΔH=5 T at T=350 K. The variation in composition of Ni2MnGa can drastically change the magnetic state of the martensitic phase below and in the vicinity of TM. The presence of the martensitic phase with magnetic moment much smaller than that in the austenitic phase above TM leads to the large inverse MCE in the Ni42Co8Mn32−yFeyGa18 system. The adiabatic change of temperature (ΔTad) in the vicinity of TC and TM of Ni50Mn35In15 and Ni50Mn35In14Z (Z=Al, Ge) was found to be ΔTad=−2 K and 2 K for ΔH=1.8 T, respectively. It was observed that |ΔTad|≈1 K for ΔH=1 T for both types of transitions. The results on resistivity, magnetoresistance, Hall resistivity in some In-based alloys are discussed. 相似文献
12.
Polycrystalline rare-earth hexaborides (NdxGdl-x)B6 (x = 0, 0.2, 0.6, 0.8, 1) were prepared by the reactive spark plasma sintering (SPS) method using mixed powder of GdH2, NdH2 and B. The effects of Nd doping on the crystal structure, the grain orientation, the thermionie emission and the magnetic properties of the hexaboride were investigated by X-ray diffraction, electron backscattered diffraction and magnetic measurements. It is found that all the samples sintered by the SPS method exhibit high densities (〉95%) and high values of Vickers hardness (2319 kg/mm2). The values are much higher than those obtained in the traditional method. With the increase of Nd content,the thermionic emission current density increases from 11 to 16.30 A/cm2 and the magnetic phase transition temperature increases from 5.85 to 7.95 K. Thus, the SPS technique is a suitable method to synthesize the dense rare-earth hexaborides with excellent properties. 相似文献
13.
《Journal of magnetism and magnetic materials》2001,223(2):127-132
The cobalt cadmium ferrite has an n-type conductivity. As the Cd addition (x) increases, the hopping rate increases and so the conductivity increases up to x=0.5. A sudden decrease in the hopping rate occurs above x=0.5 due to the decrease of Co2+ ions on octahedral sites. Above x=0.7, the hopping rate increases again and the conductivity increases. As the hopping length increases the conductivity decreases, i.e. conductivity is inversely proportional to hopping length, but is directly proportional to the hopping rate of electrons. As the ferrous ions increase on octahedral sites, the conductivity increases and the jumping length decreases leading to the increase of dielectric constant. 相似文献
14.
Time-dependent hybrid density functional theory in combination with Onsager reaction field model and super-molecular model has been applied to study solvent effects on the geometrical and electronic structures, as well as one/two-photon absorption properties, of 4-(N-(2-hydroxyethyl)-N-methyl)-amino-4'-nitroazobenzene. It is found that the short-range interaction has a large effect on the electronic structure of the solute molecule, namely, large red-shift of the maximum one-photon absorption is induced by hydrogen bonding. The solute molecule has a large two-photon absorption cross section, which is enhanced by the solvent effect. The computational results are in good agreement with measurements.[第一段] 相似文献
15.
The effects of annealing temperature and manganese substitution on the formation, microstructure and magnetic properties of MnxZn1−xFe2O4 (with x varying from 0.3 to 0.9) through a solid-state method have been investigated. The correlation of the microstructure and the grain size with the magnetic properties of Mn–Zn ferrite powders was also reported. X-ray diffraction (XRD), a scanning electron microscope (SEM) and a vibrating sample magnetometer (VSM) were utilized in order to study the effect of variation of manganese substitution and its impact on crystal structure, crystalline size, microstructure and magnetic properties of the ferrite powders formed. The XRD analysis showed that pure single phases of Mn–Zn ferrites were obtained by increasing the annealing temperature to 1200–1300 °C. Increasing the annealing temperature to ?1300 °C led to abnormal grain growth with inter-granular pores and this led to a decrease in the saturation magnetization. Moreover, an increase in the Mn2+ ion substitution up to x=0.8 increased the lattice parameter of the formed powders due to the high ionic radii of the Mn2+ ion. Mn–Zn ferrites phases were formed and the positions of peaks were shifted by substituting manganese. The average crystalline size was increased by increasing the annealing temperature and decreased by increasing the substitution by manganese up to 0.8. The average crystalline size was in the range 95–137.3 nm. The saturation magnetization of the Mn–Zn-substituted ferrite powders increased continuously with an increase in the Mn concentration up to 0.8 at annealing temperatures of 1200–1300 °C. Further increase of Mn substitution up to 0.9 led to a decrease of saturation magnetization. The saturation magnetization increased from 17.3 emu/g for the Mn0.3Zn0.7Fe2O4 phase particles produced to 59.08 emu/g for Mn0.8Mn0.2Fe2O4 particles. 相似文献
16.
Liang Xu Shuankui Li Zhiguo Wu Huajun Li De Yan Chunyu Zhang Pengju Zhang Pengxun Yan Xudong Li 《Applied Physics A: Materials Science & Processing》2011,103(1):59-65
Nanotip arrays of amorphous carbon with embedded hexagonal diamond nanoparticles were prepared at room temperature for use
as excellent field emitters by a unique combination of anodic aluminum oxide (AAO) template and filtered cathodic arc plasma
(FCAP) technology. In order to avoid nanopore array formation on the AAO surface, an effective multi-step treatment employing
anodization and pore-widening processes alternately was adopted. The nanotips were about 100 nm in width at the bottom and
150 nm in height with density up to 1010 cm−2. Transmission electron microscopy investigation indicates that many nanoparticles with diameters of about 10 nm were embedded
in the amorphous carbon matrix, which was proved to be hexagonal diamond phase by Raman spectrum and selected-area electron
diffraction. There is no previous literature report on the field emission properties of hexagonal diamond and its preparation
at room temperature under high-vacuum condition. The nanotip arrays with hexagonal diamond phase exhibit a low turn-on field
of 0.5 V/μm and a threshold field of 3.5 V/μm at 10 mA/cm2. It is believed that the existence of hexagonal diamond phase has improved the field emission properties. 相似文献
17.
A group of B-site partially substituted strontium cobaltites Sr0.9Ca0.1Co0.9B'0.1O2.5+δ (B'=Mn, Co, Ni, In, Fe and Al) were examined for phase transformation and oxygen permeation properties. As revealed by XRD
analysis, these oxides had 2H-BaNiO3-type structure (B'=Mn, Co, Ni and In) or brownmillerite-type structure (B'=Fe and Al) and transformed into perovskite-type
structure at elevated temperatures (750 °C or above). The transformation temperature was dependent on the B-site substituent
and agreed well with the switching-on temperature of oxygen permeation for the same oxide. Due to a lowering in transformation
temperature, the Fe- or Al-doped oxide was made oxygen permeable in the lower temperature range 750–850 °C where the undoped
oxide remained non-permeable. It was also found that for a series of Fe-partially substituted samples Sr0.9Ca0.1Co1−xFexO2.5+δ the transformation temperature lowered with increasing x up to 0.1, while, for x≥0.2, perovskite-type structure tended to
be stabilized at room temperature. TGDTA analysis revealed that phase transformation was accompanied by absorption or desorption
of oxygen. Based on the correlation between the oxygen permeability and the membrane thickness, the rate-determining step
of oxygen permeation in the present system was assumed to be of the bulk diffusion of oxide ion vacancies. 相似文献
18.
High near-infrared transparency Tm3+-doped germanate bulk glass and fiber have been fabricated and 2 μm emission properties demonstrated. Energy-transfer processes
in the germanate glass and fiber are discussed. The emission spectra are obtained from both bulk glass and fiber with the
excitation of a 794 nm laser diode. The results indicate that the line width of the Tm3+:3F4→3H6 emission spectra measured in fibers is narrower than that of the bulk glass sample and shifts to longer wavelengths with
increment of fiber length. The extended overlap integral method is used to calculate the microparameters of energy transfer
and critical distance. A model is derived to better understand of the energy-transfer process of thulium ions in the germanate
glasses responsible for emission at 2 μm. The study indicates that Tm3+-doped germanate fibers with a large core diameter has proved to be promising infrared optical and high-power level laser
materials. 相似文献
19.
Arif Nesrullajev 《Phase Transitions》2013,86(5):326-337
In this work, the effect of thin films on the thermo-morphologic and thermotropic properties of the phase transitions between the nematic mesophase and isotropic liquid has been investigated. Investigations have been carried out for both the heating and cooling processes. The temperature and linear widths of the biphasic regions of the direct and reverse phase transitions in nematic liquid crystals versus thickness of the thin films have been calculated with a high accuracy. The shift of the nematic mesophase–isotropic liquid and the isotropic liquid–nematic mesophase phase transition temperatures to higher temperatures and the enlargement of the temperature and linear widths of the biphasic regions as the effect of surfaces have been found. 相似文献
20.
The effect of Co substitution on the structure and magnetic properties of mechanically alloyed Pr14Tb2Fe76−xCoxC6B2 and Pr16Fe76−xCoxC6B2 (x=0–20) alloys has been studied systematically. The main phase in the alloys is Pr2Fe14C-type carbide, coexisting with a small amount of α-Fe and rare-earth-rich phases. In addition to the increasing of the Curie temperature of the Pr2Fe14C-type phase, Co substitution can affect the magnetic properties by adjusting the α-Fe fraction of the alloys. The increase of both coercivity and remanence has been realized in a certain composition range. This increase may be attributed mainly to the enhancement of the effective anisotropy constant Keff of the magnets due to the reduced α-Fe fraction with a small Co addition. The highest coercivity iHc of 20.3 kOe and the optimum energy product (BH)max of 10.3 MG Oe have been obtained for the Pr14Tb2Fe69.5Co6.5C6B2 alloy. 相似文献