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1.
In this investigation the composite SiOx〈Ti〉 films were prepared by the thermal evaporation of a mixture of silicon oxide (SiO2) and Тi powders. The optical transmission of the films in the IR spectral range and their temperature-sensitive properties are studied. By varying the contents of the metal in vaporizer and time of evaporation it is possible to obtain SiOx〈Ti〉 layers with resistance (for monopixel of 0.8 × 1 mm) from tens kOhms to MOhms and a value of the temperature coefficient of resistance (TCR) is equal to −2.22% K−1. IR spectrum of SiOx〈Ti〉 film is characterized by a broad absorption band in the range of 8–12 μm which is associated with the Si–O–Si stretching mode.Investigations of the effect of gamma irradiation on SiOx〈Ti〉 films have shown that their temperature-sensitive properties, in particular TCR does not change up to a dose of 106 Gy.These results suggest that SiOx〈Ti〉 films can be used as materials for production of radiation-resistant thermosensitive detectors operated in radiation fields of γ-radiation and combining functions of IR-absorption and formation of an electric signal. 相似文献
2.
《Journal of Physics and Chemistry of Solids》2002,63(6-8):969-973
Magnetic susceptibility (χ) and 51V NMR have been measured in (V1−xTix)2O3 near the phase boundary of the metal–insulator transition. It is established that the transition from antiferromagnetic insulating (AFI) to antiferromagnetic metallic phases near xc≈0.05 is not quantum critical, but is discontinuous with a jump of the transition temperature. In the AFI phase at 4.2 K, we observed the satellite in the zero-field 51V NMR spectrum around 181 MHz in addition to the ‘host’ resonance around 203 MHz. The satellite is also observable in the paramagnetic metallic phase of the x=0.055 sample. We associated the satellite with the V sites near Ti, which are in the V3+-like oxidation state, but has different temperature dependence of the NMR shift from that of the host V site. The host d-spin susceptibility for x=0.055 decreases below ∼60 K, but remains finite in the low-temperature limit. 相似文献
3.
《Current Applied Physics》2008,8(1):110-113
The chemical pressure control in (Sr2−xCax)FeMoO6 (0 ⩽ x ⩽ 2.0) with double perovskite structure has been investigated systematically. We have performed first-principles total energy and electronic structure calculations for x = 0 and x = 2.0. The increasing Ca content in (Sr2−xCax)FeMoO6 samples increases the magnetic moment close to the theoretical value due to reduction of Fe/Mo anti-site disorder. An increasing Ca content results in increasing (Fe2+ + Mo6+)/(Fe3+ + Mo5+) band overlap rather than bandwidth changes. This is explained from simple ionic size arguments and is supported by X-ray absorption near edge structure (XANES) spectra and band structure calculations. 相似文献
4.
《Solid State Ionics》2006,177(1-2):121-127
Lithium cobalt vanadate LixCoVO4 (x = 0.8; 1.0; 1.2) has been prepared by a solid state reaction method. The XRD analysis confirms the formation of the sample. A new peak has been observed for Li1.0CoVO4 and for Li1.2CoVO4 indicating the formation of a new phase. The XPS analysis indicates the reduction in the oxidation of vanadium and oxygen with the addition of Li in LixCoVO4 (x = 0.8, 1.0, 1.2). The impedance analysis gives the conductivity value as 2.46 × 10− 5, 6.16 × 10− 5, 9 × 10− 5 Ω− 1 cm− 1 for LixCoVO4 (x = 0.8; 1.0; 1.2), all at 623 K. The similarity in the bulk activation energy (Ea) and the activation enthalpy for migration of ions (Eω) indicate that the conduction in Li1.2CoVO4 has been due to hopping mechanism. 相似文献
5.
《Journal of Physics and Chemistry of Solids》2014,75(4):505-511
Ag-doping TiO2 composite nanotubes (Ag-TNTs) were synthesized by alkaline fusion followed by hydrothermal treatment. The microstructure and morphology of the materials were characterized by XRD, TEM, XPS, SPS (surface photovoltage spectroscopy), FISPS (electric field-induced surface photovoltage spectroscopy) and Raman spectroscopy. First-principles calculations based on density-functional theory (DFT) showed the formation of several impurity levels near the top of the valence band in the band gap (Eg) of rutile TiO2 due to Ag doping. A “double junction” is proposed, involving a Schottky junction and p–n junction (denoted as “Ag-p–n junction”) occurring between the Ag particles and the nanotube surface, as well as forming inside TiO2 nanotubes, respectively. The strongly built-in electric field of the junctions promotes the separation of photo-holes and photoelectrons, enhancing the photocatalytic efficiency. XRD results indicated that the composite Ag-TNTs exist as a mixture of anatase and rutile phases. XPS results showed that Ti4+ is the primary state of Ti. Raman spectral analysis of Ag-TNTs revealed the presence of a new peak at 271 cm−1. The red-shift of the absorption light wavelength of Ag-TNTs was 0.16 eV (20 nm) due to a considerable narrowing of Eg by the existing impurity levels. 相似文献
6.
《Superlattices and Microstructures》1999,26(4):251-261
Using the semiclassical coherent radiation—semiconductor interaction model, optical nutation has been analysed in aGaAs / AlxGa1 − xAs quantum well structure (QWS) assumed to be immersed in a moderately strong magnetic field and irradiated by a not-too-strong near band gap resonant femtosecond pulsed Ti–sapphire laser. The finite potential well depth of the QWS and the Wannier–Mott excitonic structure of the crystal absorption edge is taken into account. The excitation intensity is assumed to be below the Mott transition where the various many-body effects have been neglected with adequate reasoning. Numerical analysis made for a GaAs quantum well of thickness ∼ 100 Åand the confining layers ofAlxGa1 − xAs withx = 0.3 at intensity I ≤ 5 × 106Wcm − 2reveals that the real and imaginary parts of the transient complex-induced polarization are enhanced with an increase in the magnetic field and their ringing behaviour confirms the occurrence of optical nutation in the QWS. 相似文献
7.
Composition Bi4V2−xSrxO11−δ (0.05≤x≤0.20) is synthesized by melt quench technique followed by heat treatment at 800 °C for 12 h. These compounds are characterised by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, UV–visible spectroscopy, impedance spectroscopy and scanning electron microscopy. X-ray diffraction patterns of all the samples show γ-phase stabilization at room temperature except x=0.05 heat treated sample. The optical band gap of all the samples is observed in semiconducting range. The lowest and the highest optical band gap is 2.39 eV and 2.57 eV for x=0.10 heat treated and x=0.20 quenched samples, respectively. The highest value of dielectric constant is obtained ~107 with very low dielectric loss for x=0.15 and 0.20 samples at ~350 °C and below 10 Hz. The grain size increases with dopant concentration leads to increase the dielectric constant. 相似文献
8.
《Solid State Ionics》2006,177(33-34):2889-2896
Chromium-containing NASICON-related phosphates of the type Na(1+x)CrxM(2−x)P3O12) (M = Ti, Hf, Zr) have been synthesised by solid state reaction and structurally characterised by Rietveld refinement of the powder X-ray diffraction data. Materials of composition A(1+x)/2CrxZr(2−x)P3O12 (A = Cd, Ca, Sr), have also been prepared and characterised. The crystal structure of Na(1+x)CrxM(2−x)P3O12 corresponds to R-3c symmetry for x values ranging from 0.15 to 2.00, whereas compounds of composition A(1+x)/2CrxZr(2−x)P3O12 corresponding to R-3c are obtained when x ≤ 1.00 for Sr2+ and Ca2+, and x ≤ 1.50 for Cd2+. The polarizing effect of the two different metal ions A and M on the phosphorus atom and the P–O bond was studied by both 31P MAS NMR and infrared spectroscopy and shows that the electron density on the phosphorus, and thus the strength of the P–O bonds, are affected by both the interstitial (A) and the structural (M) metal ions. 相似文献
9.
An empirical expression for the energy bandgap as a function of alloy composition x and temperature for In1−xAlxSb was reported. The In1−xAlxSb epitaxial layers were grown by molecular beam epitaxy (MBE) on InSb(1 0 0) substrate, utilizing a p+–p+–n–n+ structure. High resolution X-ray diffraction was used to characterize the epitaxial layers. The Al composition of 2.8% was obtained by assuming the Bragg’s formula and Vegard’s law. Spectral response measurement of the diodes has been employed to investigate the temperature dependence of the band gap of In1−xAlxSb alloys in the range between 77 K and 260 K. The calculated results for energy gap of InAlSb were in good agreement with the available data and our experimental observation. 相似文献
10.
Photocatalysts Bi4Ti3 ? xCrxO12(x = 0.00, 0.06, 0.15, 0.30, 0.40, and 0.50) with perovskite structure were synthesized by sol–gel method and their electronic structures and photocatalytic activities were investigated. The Bi4Ti2.6Cr0.4O12 photocatalyst exhibited the highest performance of H2 evolution in methanol aqueous solution (58.1 μmol h? 1 g? 1) under visible light irradiation (λ > 400 nm) without a co-catalyst, whereas no H2 evolution is observed for Bi4Ti3O12 under the same conditions. The UV–vis spectra indicated that the Bi4Ti2.6Cr0.4O12 had strong photoabsorption in the visible light region. The results of density functional theory (DFT) calculation illuminate that the conduction bands of Bi4Ti3O12 are mainly attributable to the Ti 3d + Bi 6p orbitals, and the valence bands are composed of O 2p + Bi 6s hybrid orbitals, while the conduction bands of chromium-doped Bi4Ti3O12 are mainly attributable to the Ti 3d + Bi 2p + Cr 3d orbitals, and the O 2p + Cr 3d hybrid obitals are the main contribution to the valence band. 相似文献
11.
《Current Applied Physics》2009,9(3):667-672
Zn1−xMnxO thin films have been synthesized by chemical spray pyrolysis at different substrate temperatures in the range, 250–450 °C for a manganese composition, x = 15%, on corning 7059 glass substrates. The as-grown layers were characterized to evaluate their chemical and physical behaviour with substrate temperature. The change of dopant level in ZnO films with substrate temperature was analysed using X-ray photoelectron spectroscope measurements. The X-ray diffraction studies revealed that all the films were strongly oriented along the (0 0 2) orientation that correspond to the hexagonal wurtzite structure. The crystalline quality of the layers increased with the increase of substrate temperature up to 400 °C and decreased thereafter. The crystallite size of the films varied in the range, 14–24 nm. The surface morphological studies were carried out using atomic force microscope and the layers showed a lower surface roughness of 4.1 nm. The optical band gap of the films was ∼3.35 eV and the electrical resistivity was found to be high, ∼104 Ω cm. The films deposited at higher temperatures (>350 °C) showed ferromagnetic behaviour at 10 K. 相似文献
12.
T.Y. Chen S.X. Huang Z. Tesanovic R.H. Liu X.H. Chen C.L. Chien 《Physica C: Superconductivity and its Applications》2009,469(9-12):521-528
The superconducting gap in FeAs-based superconductor SmFeAs(O1?xFx) (x = 0.15 and 0.30) and the temperature dependence of the sample with x = 0.15 have been measured by Andreev reflection spectroscopy. The intrinsic superconducting gap is independent of contacts while many other “gap-like” features vary appreciably for different contacts. The determined gap value of 2Δ = 13.34 ± 0.47 meV for SmFeAs(O0.85F0.15) gives 2Δ/kBTC = 3.68, close to the BCS prediction of 3.53. The superconducting gap decreases with temperature and vanishes at TC, in a manner similar to the BCS behavior but dramatically different from that of the nodal pseudogap behavior in cuprate superconductors. 相似文献
13.
H. Calvo del Castillo J.L. Ruvalcaba M. Bettinelli A. Speghini M. Barboza Flores T. Calderón D. Jaque J. García Solé 《Journal of luminescence》2008,128(5-6):735-737
Ionoluminescence spectra for different rare-earth ion (Pr3+ and Eu3+)-activated SrxBa1?xNb2O6 strontium barium niobate crystals (x=0.33 and 0.60) have been induced with a 3 MeV proton beam for a variety of beam current intensities (45, 40 and 20 nA). The proton-beam induced luminescent spectra have shown features associated with the presence of the rare-earth ion and some spectral features mostly related to the host crystal, which appear only for high beam current intensities. We have compared the ionoluminescence results to those obtained under UV light excitation (photoluminescence technique) where a direct excitation of the band gap would occur. 相似文献
14.
Wide band gap semiconductor alloys, MgxZ1−xTe (Z=Zn, Cd and Hg), are investigated over a full range of Mg compositions (0≤x≤1) using density functional theory (DFT). The variation in the lattice constant of MgxZ1−xTe is linear with the composition x, and all these alloys obey Vegrd's law. The CdTe (6.50 Å) and MgTe (6.44 Å) are lattice matched compounds, therefore the lattice constant of MgCdTe decreases slightly with the concentration x, whereas the lattice constant also decreases for MgHgTe but increases for MgZnTe. It is due to the fact that Mg has larger size than Zn and smaller size than Cd and Hg. The band gap of these compounds are calculated using the modified Becke–Johnson (mBJ) exchange potential as LDA and GGA are not effective in producing the experimental band gap of a strongly correlated electron system. The calculated band gaps of these compounds cover the range 0–3.5 eV and are consistent with the experimental band gaps. The band gaps exhibit nonlinear behavior or bowing effect with the change in concentration. The frequency dependent optical properties like dielectric functions, and indices of refraction of these ternary systems are also calculated and discussed. 相似文献
15.
Zhengliang Wang Yaling Zhang Li Xiong Xiaofan Li Junming Guo Menglian Gong 《Current Applied Physics》2012,12(4):1084-1087
New red tungstates phosphors, Na5La1?xLnx(WO4)4 (Ln = Eu, Sm) and Na5Eu1?xSmx(WO4)4, were prepared by solid-state reaction technique. And their structure and photo-luminescent properties were investigated. The introduction of Sm3+ broadened the excitation band around 400 nm of the phosphors, and strengthened the red emission. And the possible energy transfer process from Sm3+ to Eu3+ is discussed. The single red LED was fabricated by combining InGaN chip with Na5Eu0.94Sm0.06(WO4)4 as red phosphor, intense red light can be observed by naked eyes. Then the phosphor Na5Eu0.94Sm0.06(WO4)4 may be a good candidate for red component of near-UV InGaN-based W-LEDs, because of efficient red-emitting with broadened absorption around 400 nm and appropriate CIE chromaticity coordinates (x = 0.65, y = 0.34). 相似文献
16.
J. Ishida K. Murata T. Ichikawa A. Hirano N. Imanishi Y. Takeda O. Yamamoto 《Solid State Ionics》2009,180(17-19):1045-1049
Mixed electron hole and oxide ion conducting perovskite-type oxides, La0.8Sr0.2(Ga0.8Mg0.2)1 ? xCrxO3 ? δ (0 ≤ x ≤ 1.0), were prepared by solid state reaction. The phase stability and the oxygen permeation properties of the oxides were examined as a function of the content of Cr. La0.8Sr0.2(Ga0.8Mg0.2)1 ? xCrxO3 ? δ has a perovskite related tetragonal phase with x = 0.1 to 0.8. The total electrical conductivity of La0.8Sr0.2(Ga0.8Mg0.2)1 ? xCrxO3 ? δ increases with increasing x. The oxygen permeation flux across the La0.8Sr0.2(Ga0.8Mg0.2)1 ? xCrxO3 ? δ membranes at higher temperatures increases with x up to x = 04. The maximum oxygen permeation flux of 1.6 × 10? 7 mol? 1 cm? 2 at 1100 °C in a oxygen activity gradient of air/10? 2 Pa is observed in La0.8Sr0.2(Ga0.8Mg0.2)0.6Cr0.4O3 ? δ. This perovskite-type oxide is stable under an oxygen partial pressure of 7 × 10? 10 Pa at 1000 °C. 相似文献
17.
Synthesis,characterization and photovoltaic properties of novel molecules based on triarylamine dyes
《Current Applied Physics》2010,10(3):749-756
We report the synthesis, electrochemical and photovoltaic properties of triphenylamine based novel organic sensitizer, comprising donor, electron-conducting and anchoring group. Different triphenylamines were synthesized as donor unit and connected to cyano-acidic acid acceptor over vinyl group. In this work, we studied on two novel dyes (TPA2, TPA3) by attaching methyl to m-position and diphenylamine to p-position of the basic triphenylamine structure, respectively. All derivatives absorb at visible region of solar spectrum in the range of 350–632 nm. By introducing strong electron injection groups to triphenylamine ring, band gap becomes narrower while EHOMO–ELUMO levels are tuned. All current voltage (I–V) measurements were done under 100 mW/cm2 light intensity and AM 1.5 conditions. TPA3 chromophore with the lowest band gap shows the best cell performance with an efficiency (η) of 4.12%, a short-circuit photocurrent density (Isc) of 8.07 mA/cm2, an open-circuit voltage (Voc) of 714 mV and a fill factor (FF) of 0.72. 相似文献
18.
《Solid State Ionics》2006,177(19-25):1849-1853
Single phase materials of the La(2−x)SrxMnO4±δ (0.6 ≤ x ≤ 2.0) solid solution series were prepared via solid state reaction. The structure of each material was examined at room temperature and determined to be tetragonal for all phases examined. An expansion in lattice volume was observed on increasing lanthanum content. The stability and thermal expansion of each member of the solid solution series was determined via the use of in situ high temperature X-ray diffraction. It was found that all materials remained stable up to a temperature of 800 °C. Thermal expansion coefficients were found to be in the region of 15 × 10− 6 K− 1 for La(2−x)SrxMnO4±δ compounds where x > 1.4. The electrical conductivity of each phase was also determined over a similar temperature range with a maximum value of ∼6 Scm− 1 at 900 °C for the x = 1.8 phase. 相似文献
19.
M. Ferhi K. Horchani-Naifer S. Hraiech M. Férid Y. Guyot G. Boulon 《Optics Communications》2012,285(12):2874-2878
The polycrystalline powders of condensed polyphosphates KLa(1 ? x)Ybx(PO3)4 (x = 5, 10, 15, 20%) with linear chain were prepared by solid-state reaction. These samples were characterized by X-ray diffraction, FTIR and Raman scattering spectroscopies. The obtained powders are formed by single monoclinic phase of type III of condensed polyphosphate KLa(PO3)4 (KLP) crystallized with P21 space group. Lattice parameters varied as a function of the ytterbium concentration. As the Yb3+ concentration increased, the crystal lattice parameters were decreased. For the first time, near infrared (NIR) and UV–Visible spectroscopy of Yb3+ in KLa(PO3)4 powders, at room temperature, are carried out. In the IR range, a broad band relative to the fundamental 2F5/2 → 2F7/2 emission was registered. In the UV–Visible spectra, two bands typical of the Yb3+ charge transfer band (CTB) luminescence are observed. The registered decay times of these two emission types showed low sensibility to the Yb3+ concentration in KLa(PO3)4. 相似文献
20.
《Journal of magnetism and magnetic materials》2001,225(3):389-393
Microstructure and magnetic properties of melt-spun nanocomposite magnets with nominal compositions of (Nd1−xPrx)9Fe86B5 (x=0–1) were investigated. Substitution of Nd by Pr could significantly improve the hard magnetic properties of the nanocomposite magnets; the intrinsic coercivity (iHc) and the maximum magnetic energy product ((BH)max) increase from 414 kA/m and 124 kJ/m3 for x=0 to 493 kA/m and 152 kJ/m3 for x=0.6, respectively. Further substituting Nd by Pr (x>0.6) strongly weakens exchange-coupling interaction between magnetically hard and soft phases. 相似文献