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1.
Multilayer relaxation at high-index Cu(n, n−1, 0) (n=2, 3 and 4) stepped surfaces was determined by the first-principles pseudopotential plane wave (PPPW) method. For those surfaces that have n and n−1 atom-rows in terrace and subterrace, respectively, the topmost 2n−2 interlayer spacings contract, while the 2n−1st interlayer spacing expands. There is no similar rule found for the relaxations parallel to the surfaces. Compared with the bulk terminated structure, a thin compact layer, which consisted of the topmost 2n−1 atom layers and separated slightly from the underneath atom layers, makes the surface more flat after relaxation. The bond-lengths between the step edge (first layer) atom and its nearest-neighbors do not depend on the surface termination, but only on the local coordination.  相似文献   

2.
Optical absorption at room temperature and electrical conductivity at temperatures between 283 and 333 K of vacuum evaporated GexFexSe100−2x (0≤x≤15) amorphous thin films have been studied as a function of composition and film thickness. It was found that the optical absorption is due to indirect transition and the energy gap increases with increasing both Ge and Fe content; on the other hand, the width of the band tail exhibits the opposite behavior. The optical band gap Eopt was found to be almost thickness independent. The electrical conductivity show two types of conduction, at higher temperature the conduction is due to extended states, while the conduction at low temperature is due to variable range hopping in the localized states near Fermi level. Increasing Ge and Fe contents were found to decrease the localized state density N(EF), electrical conductivity and increase the activation energy for conduction, which is nearly thickness independent. Variation of the atomic densities ρ, molar volume V, glass transition temperature Tg cohesive energy C.E and number of constraints NCo with average coordination number Z was investigated. The relationship between the optical gap and chemical composition is discussed in terms of the cohesive energy C.E, average heat of atomization and coordination numbers.  相似文献   

3.
Layered SrBi2(Nb1−xVx)2O9−δ (SBVN) ceramics with x lying in the range 0-0.3 (30 mol%) were fabricated by the conventional sintering technique. The microstructural studies confirmed the truncating effect of V2O5 on the abnormal platy growth of SBN grains. The electrical conductivity studies were centred in the 573-823 K as the Curie temperature lies in this range. The concentration of mobile charge carriers (n), the diffusion constant (D0) and the mean free path (a) were calculated by using Rice and Roth formalism. The conductivity parameters such as ion-hopping rate (ωp) and the charge carrier concentration (K′) term have been calculated using Almond and West formalism. The aforementioned microscopic parameters were found to be V2O5 content dependent on SrBi2(Nb1−xVx)2O9−δ ceramics.  相似文献   

4.
BiFeO3 has been studied extensively due to its room temperature multiferroic features and has been proven as a promising candidate for device applications. But BiFeO3 possesses some drawbacks like high leakage current and complicated magnetic ordering, giving rise to a canted antiferromagnetic behavior. Hence, a superlattice approach of BiFeO3 and BaTiO3 with a good lattice matching was fabricated and the room temperature ferroelectric and ferromagnetic properties were studied. The macroscopic and local probe studies reveal a ferroelectric nature at room temperature, and most importantly a weak ferromagnetic like behavior was observed. The ferromagnetic behavior is expected to arise due to the variation introduced in the spin modulation of single BiFeO3 layer due to the superstructure formation.  相似文献   

5.
Highly ordered mesoporous Co3O4, NiO, and their metals were synthesized by nanocasting method using there corresponding mesoporous SBA-15 silica as a template. The obtained porous metal oxides have high surface areas, large pore volume, and a narrow pore size distribution. The N2-adsorption data for mesoporous metal oxides have provided the BET area of 257.7 m2 g−1 and the total pore volume of 0.46 cm3 g−1. The mesoporous metals were employed as a catalyst in the synthesis of (S)-3-pyrrolidinol from chiral (S)-4-chloro-3-hydroxybutyronitrile, and a high yield to (S)-3-pyrrolidinol-salt was obtained on the mesoporous Co metal catalyst.  相似文献   

6.
The 1H and 2H spin-lattice relaxation times in the monohydride phase of the V-H-D and Ti0.1V0.9-H-D systems have been re-analyzed by Bloembergen-Purcell-Pound (BPP) equations with a log-normal distribution of correlation times, and the obtained parameters have been compared with those of the Ti0.33V0.67-H-D system. The mean activation energy and the magnitude of the distribution of H and D diffusions are discussed in relation to the metal compositions, the hydrogen site, the crystal structure and the [H]/[D] ratios.  相似文献   

7.
This paper reports laboratory tests involving the dry deposition on copper surfaces of NO2, alone and in combination with SO2, at different concentrations (200 and 800 μg m−3), temperatures (15, 25 and 35 °C) and relative humidities (50%, 70% and 90%). Gravimetric results and characterisation of the corrosion products by optical microscopy, scanning electron microscopy (SEM/EDX), grazing incidence X-ray diffraction (GIXD) and X-ray photoelectron spectroscopy (XPS) show that the corrosive effect of NO2 acting alone depends greatly on the RH. At 90% RH copper behaves in the same way as in unpolluted atmospheres, while at lower RH localised attack is detected. Analysis reveals the presence of basic copper nitrate (gerhardtite, Cu2(OH)3NO3). However, in SO2-polluted atmospheres no differential behaviour with RH or temperature is observed. In these atmospheres copper corrosion is similar to that obtained in unpolluted or in NO2-polluted atmospheres at high RH, although GIXD detects basic copper sulphate (posnjakite, Cu4(OH)6SO4·2H2O). In the case of mixed atmospheres (SO2+NO2) a significant accelerating effect is observed when [NO2]>[SO2]. Otherwise an inhibitive effect is detected. At high RH in the presence of SO2, NO2 favours SO2 oxidation and finally sulphuric acid formation, which attacks the cuprite layer. S-containing compounds, especially basic copper sulphate, are easily detected by GIXD and XPS in the outermost corrosion product layer. However, at low RH, NO2 reacts preferentially with adsorbed water to produce nitrous and nitric acids that attack the cuprite layer. In this case, an outer corrosion product layer containing copper nitrite (soluble) and basic copper nitrate is formed over an intermediate layer that contains significant amounts of basic copper sulphate from the previous interaction of sulphuric acid and cuprite.  相似文献   

8.
The well known phenomenon of the increase of Tc of YBCO after slow cooling or low temperature annealing without change of the oxygen content, was found also for the YBCO like tetragonal superconductors of (CaxLa1−x)(LauBa1−u)2Cu3Oy (this compound has been previously denoted as CLBLCO, CLBCO or CaLaBaCuO). It has been observed at 150 and 100 °C for oxygen underdoped, optimally- and overdoped ceramics. The products retain their tetragonal unit cells. The possible reasons of this phenomenon are discussed.  相似文献   

9.
The solid solution (Ce1−xLax)PtGa has been studied through X-ray diffraction, magnetization (σ(B)), magnetic susceptibility (χ(T)), electrical resistivity (ρ(T)), magnetoresistivity (MR) and heat capacity (CP(T)) measurements. The Néel temperature (TN=3.3 K) for CePtGa is lowered upon La substitution as observed from χ(T) and ρ(T) measurements. The Kondo temperature TK as calculated from MR measurements is comparable to TN and also decreases with La substitution. The volume dependence of TK is in accordance with the compressible Kondo lattice model and a Doniach diagram of the results is presented. CP(T) measurements are presented for CePtGa, Ce0.2La0.8PtGa and LaPtGa and the results are discussed in terms of the electronic and magnetic properties. Other features of interest are anomalies in ρ(T) and CP(T) due to crystalline electric field effects and metamagnetism as observed in σ(B) studies for samples with 0≤x≤ 0.3.  相似文献   

10.
We have prepared a series of (PLZT)x(BiFeO3)1−x transparent thin films with thickness of 300 nm by a thermal pyrolysis method. Only films with x≦0.10 formed a single phase of perovskite structure. The film where x=0.10 exhibited both ferromagnetic and ferroelectric properties at room temperature with spontaneous magnetization and coercive magnetic fields of 0.0027μB and 5500 G, respectively. The remanent electric polarization and coercive electric field for the film where x=0.10 were 3.0 μC/cm2 and 24 kV/cm, respectively. Additionally, films with 0.02≦x≦0.10 showed both magneto-optical effects and the second harmonic generation of transmitted light.  相似文献   

11.
CuIn(SxSe1−x)2 thin polycrystalline films were grown by the chemical spray pyrolysis method on the glass substrate at 280-400°C. The alloy composition in the film was studied with relation to that in the splay solution. Films were characterized by X-ray diffraction, optical absorption, Raman spectroscopy, resistivity and surface morphology. The CuInSe2-rich alloy films grown at high substrate temperature had chalcopyrite structure, while, the CuInS2-rich films grown at low substrate temperature exhibited sphalerite structure. Optical-gap energies were smaller than that of the bulk crystal by 0.1-0.2 eV for CuInS2-rich films. Raman spectra exhibited both CuInSe2-like and CuInS2-like A1 modes, and their relative changed systematically with alloy composition.  相似文献   

12.
The electrical conductivity (σ) of (EryU1−y)O2+x (y=0.06, 0.20) and (CeyU1−y)O2+x (y=0.05, 0.15, 0.25) has been measured as a function of oxygen partial pressure in the temperature range of 1100≤T/°C≤1300 by a d.c. 4-probe method. Both of the oxides exhibited Po2-regions where the electrical conductivity is independent of oxygen partial pressure, which indicates that doped Er and Ce exist as trivalent cations on uranium sites and fix the hole concentration by acting as electron acceptors, i.e. [h]=[Er′U] and [h]=[Ce′U], respectively. It is considered that strong oxidization tendency of uranium and reduction tendency of cerium simultaneously render the cerium ions exist exclusively as Ce3+ in the uranium dioxide. The electron-hole mobility of (EryU1−y)O2+x and (CeyU1−y)O2+x in the Po2 region where σ is constant has been calculated by the combination of the electrical conductivity and charge carrier concentration; the activation energy (EH) of each oxide has been obtained from the temperature dependence of the mobility. Small polaron hopping conduction mechanism was confirmed by small magnitude of the mobility (0.018-0.052 cm2 V−1 s−1) and the activation energy (0.12-0.22 eV).  相似文献   

13.
A series of SmCoAsO1−xFx (with x=0, 0.05, 0.1, and 0.2) samples have been prepared by solid state reactions. X-ray powder diffraction proved that all samples can be indexed as a tetragonal ZrCuSiAs-type structure. A clear shrinkage of the lattice constants a and c with increasing F content indicated that F has been doped into the lattice. The magnetic and transport properties of the samples have been investigated. Parent SmCoAsO compound exhibited complicated magnetism including antiferromagnetism, ferromagnetism, and ferrimagnetism. For the fluorine doped samples, the antiferromagnetic Néel temperatures were almost independent of the F content and metamagnetic transitions were observed below antiferromagnetic Néel temperatures. With increasing F content, high temperature (below 142 K) ferrimagnetic state gradually changed to ferromagnetic state. In the resistivity result, metallic conduction in the region of 2-300 K and Fermi liquid behavior at low temperatures were shown in all samples. Transport properties at applied magnetic fields showed anomalies at low temperatures.  相似文献   

14.
We have incorporated the translational rotational (TR) coupling effects in the framework of three body force shell model (TSM) to develop an extended TSM (ETSM). This ETSM has been applied to reveal the second order elastic constants (C11, C12 and C44) in the dilute regimes 0≤x≤0.50. Our theoretical results have reproduced well the observed variations of C11 (x=0.14, 0.43) and C12 (x=0.14, 0.43) with temperature. The anomalous elastic behaviour observed in C44 below 150 K for x=0.43 has been predicted well by ETSM results in the orientationally disordered (NH4I)x(KI)1−x mixed crystals. Our results for C12 are in good agreement with the experimental data available for x=0.14 and 0.43. Besides, the third and fourth order elastic constants and the results on cohesive and thermophysical properties are also discussed.  相似文献   

15.
X-ray diffraction experiments have been combined with Raman scattering and transmission electron microscopy data to analyze the result of rapid thermal annealing (RTA) applied to Zr films, 16 or 80 nm thick, sputtered on Si1−xGex epilayers (0≤x≤1). The C49 Zr(Si1−xGex)2 is the unique phase obtained after complete reaction. ZrSi1−xGex is formed as an intermediate phase. The C49 formation temperature Tf is lowered by the addition of Ge in the structure. Above a critical Ge composition close to x=0.33, a film microstructure change was observed. Films annealed at temperatures close to Tf are continuous and relaxed. Annealing at T>Tf leads to discontinuous films: surface roughening resulting from SiGe diffusion at film grain boundaries occurred. Grains are ultimately partially embedded in a SiGe matrix. A reduction in the lattice parameters as well as a shift of Raman lines are observed as T exceeds Tf. Both Ge non-stoichiometry and residual stress have been considered as possible origins for these changes. However, as Ge segregation has never been detected, even by using very efficient techniques, it is thought that the changes originate merely from residual stress. The C49 grains are expected to be strained under the SiGe matrix effect and shift of the Raman lines would indicate the stress is compressive. Some simple evaluations of the stress values indicate that it varies between −0.3 and −3.5 GPa for 0≤x≤1 which corresponds to a strain in the range (−0.11, −1.15%). X-ray and Raman determinations are in good agreement.  相似文献   

16.
The effect of non-magnetic Zn impurity on superconductivity in electron-type pnictide superconductor LaFe0.925−yCo0.075ZnyAsO is studied systematically. The optimally doped LaFe0.925Co0.075AsO without Zn impurity exhibits superconductivity at Tcmid of 13.2 K, where Tcmid is defiend as the mid-point in the resistive transition. In the presence of Zn impurity, the superconducting transition temperature, Tcmid, is severely suppressed. The result is consistent with the theoretic prediction on the effect of non-magnetic impurity in the scenario of s± pairing, but it is in sharp contrast to the previous report on the effect of Zn impurity in the F-doped systems. The possible interpretation of the different effects of Zn impurity on superconductivity in different systems is discussed.  相似文献   

17.
Microstructure, phase transformation behavior and dielectric properties of BaTi1−x(Al1/2Nb1/2)xO3 (0.01≤x≤0.40) ceramics were investigated. A high level of (Al1/2Nb1/2)4+ substitution for Ti4+ ions was not conducive to the stability of the perovskite structure and resulted in the formation of BaAl2O4. As x was increased, lattice constants and unit cell volume decreased, reached a minimum at x=0.10 and then increased. The BaTi1−x(Al1/2Nb1/2)xO3 ceramics at room temperature experienced a transformation from ferroelectric to paraelectric phase with increasing (Al1/2Nb1/2)4+ concentration. Meanwhile, permittivity of the BaTi1−x(Al1/2Nb1/2)xO3 ceramics was markedly reduced, while Q value was slightly increased. Frequency dispersion of dielectric peak was obviously increased as x was increased from 0.01 to 0.10. It is of great interest that a dielectric abnormity represented by a broad dielectric peak at 200-400 K was observed for the composition with x=0.40.  相似文献   

18.
We investigate the oxidation of nanocrystalline aluminum surfaces using molecular dynamics (MD) simulations with the variable charge model that allows charge dynamically transfer among atoms. The interaction potential between atoms is described by the electrostatic plus (Es+) potential model, which is composed of an embedded atom method potential and an electrostatic term. The simulations were performed from 300 to 750 K on polycrystalline samples with a mean grain size of 5 nanometers. We mainly focused on the effect of the temperature parameter on the oxidation kinetic. The results show that, beyond a first linear regime, the kinetics follows a direct logarithmic law (governed by diffusion process) and tends to a limiting value corresponding to a thickness of ∼3 nm. We also characterized at 600 K the effects of an external applied strain on the microstructure and the chemical composition of oxide films formed at the surface. In particular, we obtained a partially crystalline oxide films for all temperatures and we noticed a strong correlation between the degree of crystallinity of the oxide film and the oxidation temperature.  相似文献   

19.
This paper presents a study of bulk samples synthesized of the Ag1−xCuxInSe2 semiconductor system. Structural, thermal and electrical properties, as a function of the nominal composition (Cu content) x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 were studied. The influence of x on parameters such as melting temperature, solid phase transition temperature, lattice parameters, bond lengths, crystallite size t (coherent domain), electrical resistivity, electrical mobility and majority carrier concentration was analyzed. The electrical parameters are analyzed at room temperature. In general, it is observed that the properties of the Ag1−xCuxInSe2 system for x≤0.4 are dominated by n-AgInSe2, while for x>0.4, these are in the domain of p-CuInSe2. The crystallite size t in the whole composition range (x) is of the order of the nanoparticles. Secondary phases (CuSe, Ag2Se and InSe) in small proportion were identified by XRD and DTA.  相似文献   

20.
The magnetic properties of four compounds in the series CaBaCo4−xyZnxAlyO7 (x=0,1,2, y=0,1) were investigated. Using AC-susceptibility and DC-magnetometry, magnetic transitions (Tfs) were found for all four compositions in the range 50-3 K. The data from the AC measurements proved to be frequency dependent: Tf increases with higher frequencies. An energy-loss in the magnetic coupling, indicated as contributions in the imaginary part of the magnetic susceptibility (χ″), was seen for every compound and its maximum appeared just below the maximum χ′. Modelling the data with Arrhenius-, Vogel-Fulcher-, and the power-law made it possible to relate the four compounds to spin-glass materials. The Casimir-du Pré relation was used to extract average relaxation times at Tf. The DC magnetisations clearly show differences between field-cooled and zero-field-cooled measurements. None of the compounds exhibit any metamagnetic properties up to 8 T. A new method is presented to calculate the saturation fields using DC data. Relaxation measurements on three compounds indicate that the systems relax very fast, in contrast to spin-glasses. Aging does not affect the fast relaxations. The compounds are interpreted as disordered anti-ferromagnets with spin-glass features.  相似文献   

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