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1.
Microstructure, dynamics, and diffusion mechanism in liquid MgO have been studied by molecular dynamics simulation. Models consisting of 2000 atoms were constructed under a wide range of pressure and at a temperature of 3800 K. The local structure is analyzed through the coordination number distribution and topology statistics of coordination units (basic structural units) MgO x (x=2, 3, 4, 5, 6, 7). As regards the structural dynamics, the nearest-neighbor atomic exchange among coordination units, spatially heterogeneous dynamics, clustering, and structural stability (lifetime of basic structural units) are investigated in detail. Investigation of structural dynamics allows us to gain insight into various important atomic (molecular) properties and to clarify the diffusion mechanism in liquid MgO under high pressure. 相似文献
2.
E. L. Barsukova L. I. Postnova V. I. Levchenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2012,6(3):442-445
ZnSe1 ? x S x (1 ?? x ?? 0) crystals are grown from the vapor of binary components in a closed horizontal system. The ZnSe1 ? x S x crystals doped with chromium and cobalt are prepared by post-growth diffusion. Their absorption spectra are studied depending on the composition of the solid solution and the doping level. The diffusion coefficients of chromium and cobalt at the temperature 1040°C and their dependence on composition are determined. 相似文献
3.
《Solid State Ionics》1986,21(3):225-229
The diffusion coefficient of the O2− ions in yttria-stabilized zirconia (1−x)ZrO2·xYO1.5 has been investigated as a function of the concentration of Y3+ ion over a range x = 0.131–0.261 by using quasielastic light scattering. The diffusion coefficients were deduced from the analysis of the temperature dependence of the scattering intensity at 3 GHz. It is concluded that the diffusion coefficient reaches its maximum value at x = 0.165. The composition dependence of the scattering intensity suggests that the concentration of the moving carrier decreases as the Y3+ content increases in spite of an increase of the oxygen vacancies. 相似文献
4.
The microscopic bonding behavior of amorphous Cux(As2Se3)1?x (x = 0.00, 0.01, 0.05, 0.10 and 0.20) is studied from the point of view of the viscosity. The model used in this analysis describes the temperature dependence of the viscosity in terms of the mean bond strength E0, the mean coordination number Z0, and their fluctuations ΔE, ΔZ of the structural units that form the melt. The model reproduces quite well the temperature dependence of the viscosity of Cux(As2Se3)1?x observed experimentally. According to the theory, the fragility of the system increases as the fluctuation of the total bond strength increases. It is shown that the viscous flow is accompanied by the cooperative movements of the structural units and occurs by breaking selectively the weaker parts of the bonds between the structural units. This notion is related to the concept of Cooperatively Rearranging Region (CRR) in the theory of Adam–Gibbs. By analyzing the model, the fluctuation of the total bond strength in Cu–As–Se system is evaluated quantitatively, and the composition dependence of the fragility is discussed in terms of bond strength and the coordination number between the structural units. The analysis suggests that in the Cux(As2Se3)1?x system, there must be a strong composition dependence in the bond strength and a weak composition dependence in the fragility and coordination number fluctuation. 相似文献
5.
The absorption near the fundamental edge of Cd1-xMnxSe was measured in the composition range 0<x<0.3 at room and liquid nitrogen temperature with the electric field of the radiation parallel and perpendicular to the hexagonal axis. An exponential dependence of the absorption coefficient versus photon energy was found, and a linear dependence of energy gap E0 on composition was obtained. The room temperature reflectivity measurements in the energy range 2.5–5.2eV, for two polarization of light were performed, and a linear dependence of the interband transitions energies vs. alloy composition was found. 相似文献
6.
J.W. Osenbach W.R. Bitler V.S. Stubican 《Journal of Physics and Chemistry of Solids》1981,42(7):599-603
The theoretical model developed by Lidiard was extended to describe the relationship between the chemical and tracer diffusion coefficients of aliovalent ions in an ionic lattice.It is shown that the relationship between the chemical diffusion coefficient, D, and the tracer diffusion coefficient, D1, is D = 2D1 if the migration of dimers is the principal mechanism of transport and for the migration of trimers D = 3D1 if the concentration of impurity ion is relatively small. These relationships are valid regardless of the charge of the aliovalent or lattice ions.The chemical diffusion coefficients of Cr3+ in Cr-doped MgO were determined for three different temperatures, 1656, 1717 and 1768K, and for the concentration region 2.5×10?2?2.8×10?1 mole% Cr2O3. Using previously determined values for the tracer diffusion coefficient of 51Cr in Cr-doped MgO it was found that for the temperature and concentration region investigated D = (2.00±0.17)D1 which indicates that diffusion proceeds primarily by the migration of dimers. 相似文献
7.
We present measurements of the critical behaviour of the EPR linewidths at frequencies 9.21 and 35.5 GHz. In the exchange critical region above Tc (4πx ? 1) the strong field dependence of the linewidths is observed, even when the field variation of susceptibility x is small. This phenomenon is explained by the spin diffusion effect on the linewidth. The spin diffusion coefficients D for CdCr2Se4 and CdCr2S4 are determined from the linewidths data. The temperature dependence D is found to be consistent with the predictions of the dynamical scaling theory. 相似文献
8.
《Journal of Physics and Chemistry of Solids》2007,68(5-6):1029-1034
Raman scattering has been employed to study the temperature and composition dependence of the vibrational modes for the glass-forming oxyhalide mixtures xLiCl–(1–x)TeO2 (x=0, 0.2, 0.3, 0.35, 0.5 and 0.67) in the glassy, supercooled and liquid state up to 600 °C. The analysis has shown that the network structure of the glass/melt is formed by mixing trigonal bipyramid and trigonal pyramid units. The change of LiCl content and/or temperature results to conversion of the trigonal bipyramid to trigonal pyramid units with a varying number of non-bridging chlorine and oxygen atoms. The fraction of the terminal oxygen atoms doubly bonded to tellurium versus temperature has been directly estimated from the Raman spectroscopic results with the aid of a structural model concerning the tellurite network systems. A well-resolved Boson peak (BP) dominates the low-frequency Raman spectra. The temperature dependence of the maximum of the BP has also been determined and discussed in the framework of its microscopic origin. 相似文献
9.
I.F. Mironyuk V.M. Gun’ko M.O. Povazhnyak V.M. Chelyadin J. Skubiszewska-Zi?ba 《Applied Surface Science》2006,252(12):4071-4082
Calcination of magnesium hydroxide, which was prepared from natural bischofite MgCl2·6H2O, leading to dehydration 2(MgOH) → MgOMg + H2O, is accompanied by transition of phase not only to MgO but also to MgOx at x < 1 (assigned to Mg4O3) at moderate temperatures. At higher temperatures, MgOx is completely transformed into MgO. Magnesium hydroxide and oxide heated at different temperatures were studied using the TEM, XRD, IR, PCS, TG-DTA, nitrogen and argon adsorption methods. The electronic structure of MgO and Mg4O3 was studied using the ab initio quantum chemical method with periodic conditions. According to TEM images, the morphology of particles changing from Mg(OH)2 laminae to aggregates of interpenetrated MgO cubelets and foils depend strongly on the calcination temperature. Significant changes in surface area are observed mainly at 325-470 °C on desorption of a major portion of eliminated water corresponding to 28.4 wt.% at its total amount of 30.9 wt.%. Pore size distribution (PSD) is sensitive to treatment conditions and the main PSD peaks shift towards larger pore size with elevating temperature. The characteristics of the surface hydroxyls as well as of the bulk MgO bonds depend on heating conditions, as noticeable changes are observed in the XRD patterns and the IR spectra of the samples undergoing the mentioned transformation of phase Mg(OH)2 → MgOx → MgO. 相似文献
10.
The densities and surface tensions of SexTe1?x melts have been determined from the melting points up to about 700°C. For Te-rich alloys a non linear behaviour has been found for the temperature dependence connected with a change in the coordination number. 相似文献
11.
M. P. Ivliev I. P. Raevskii L. A. Reznichenko S. I. Raevskaya V. P. Sakhnenko 《Physics of the Solid State》2003,45(10):1984-1989
The temperature dependence of dielectric constant ? for single crystals of Na1?xKxNbO3 (0.04?x?0.15) is studied for the first time. From the shape of the ?(T) anomalies corresponding to rotational phase transitions, the type of interaction between the order parameters and the polarization is determined. A phenomenological model is developed which adequately describes the experimentally observed sequence of high-temperature (T>300°C) phase transitions, the dielectric anomalies associated with these transitions, and the changes in the phase states under the action of external factors (pressure, electric field). 相似文献
12.
Antoni Bukaluk 《Czechoslovak Journal of Physics》1993,43(9-10):887-891
Studies of the interdiffusion in ion-plated Ni100- x P x /Ni100- y /P y thin films are described. The diffusion coefficients are evaluated from depth profiles obtained by using Auger electron spectroscopy (AES). The well-known Boltzmann-Matano method is applied for extraction of the diffusion coefficients from the depth profile data. The results show a strong composition dependence. 相似文献
13.
Microstructural properties of liquid and amorphous SiO2 nanoparticles have been investigated via molecular dynamics (MD) simulations with the interatomic potentials that have weak Coulomb interaction and Morse-type short-range interaction under non-periodic boundary conditions. Structural properties of spherical nanoparticles with different sizes of 2, 4 and 6 nm obtained at 3500 K have been studied through partial radial distribution functions (PRDFs), coordination number and bond-angle distributions, and compared with those observed in the bulk. The core and surface structures of liquid SiO2 nanoparticles have been studied in detail. We found significant size effects on structure of nanoparticles. Calculations also show that if the size is larger than 4 nm, liquid SiO2 nanoparticles at the temperature of 3500 K have a lightly distorted tetrahedral network structure with the mean coordination number ZSi-O≈4.0 and ZO-Si≈2.0 like those observed in the bulk. Moreover, temperature dependence of structural defects and SiOx stoichiometry in nanoparticles on cooling from the melt has been found and presented. 相似文献
14.
The short-range orders of liquid InxSn100−x binary alloys have been investigated along the liquidus based on the experimental results obtained using X-ray diffraction. The covalent bonding structures characterized by the shoulder on the high-Q side of the first peak of S(Q) for all the InxSn100−x melts are detected. With increasing Sn content, there is a rather continuous change of the local structure possibly related to the presence of nearly covalent bonds in the liquid alloy. The peculiar temperature dependence of the viscosity is assigned to the evolution of tetrahedral units. The observed correlation between liquid structures and peculiar viscosity behaviors provides new insight into nucleation phenomena from microscopic viewpoint. 相似文献
15.
The microscopic structure and dynamics of liquid TixAl1-x alloys together with pure liquid Ti and Al metals were investigated by means of molecular dynamics simulations. This work gives the structural properties, including pair-correlation function, bond-angle distribution function, HA and Voronoi indices, and their composition dependence. The dynamical properties have also been studied. The calculated pair-correlation function, bond-angle distribution function, and HA and Voronoi indices suggest that the stoichiometric composition Ti0.75Al0.25 exhibits a different local structure order compared with other concentrations, which help us understand the appearance of the minimum diffusion coefficient at this composition. These results indicate that the mobility of atoms strongly depends on their atomic local structure. 相似文献
16.
Zayani Jaafar Othman Adel Matoussi Filippo Fabbri Francesca Rossi Giancarlo Salviati 《Applied Physics A: Materials Science & Processing》2014,116(3):1501-1509
This paper reports structural, optical and cathodoluminescence characterizations of sintered Zn1?x Mg x O composite materials. The effects of MgO composition on these film properties have been analyzed. X-ray diffraction (XRD) confirms that all composites are polycrystalline with prominent hexagonal wurtzite structure along two preferred orientations (002) and (101) for the crystallite growth. Above doping content x = 10 %, the formation of the hexagonal ZnMgO alloy phase and the segregation of the cubic MgO phase start. From reflectance and absorption measurements, we determined the band gap energy which tends to increase from 3.287 to 3.827 eV as the doping content increases. This widening of the optical band gap is explained by the Burstein–Moss effect which causes a significant increase of electron concentration (2.89 × 1018?5.19 × 1020 cm?3). The luminescent properties of the Zn1?x Mg x O pellets are studied by cathodoluminescence (CL) at room and liquid nitrogen temperatures under different electron beam excitations. At room temperature, the CL spectra of the Zn1?x Mg x O composites exhibit a dominant broad yellow-green light band at 2.38 eV and two ultraviolet emission peaks at 3.24 and 3.45 eV corresponding to the luminescence of the hexagonal ZnO and ZnMgO structures, respectively. For the doped ZnO samples, it reveals also new red peaks at 1.72 and 1.77 eV assigned to impurities’ emissions. However, the CL spectra recorded at 77 K show the presence of excitonic emission peaks related to recombination of free exciton (X A), neutral donor-bound excitons (D0X) and their phonon replicas. The CL intensity and energy position of the green, red and ultraviolet emission peaks are found to depend strongly on the MgO doping content. The CL intensity of the UV and red emissions is more enhanced than the green light when the MgO content increases. CL imaging analysis shows that the repartition of the emitting centers in Zn1?x Mg x O composites is intimately connected to the film composition and surface morphology. 相似文献
17.
A. Kaiser D. Banerjee C. Wiemann C.M. Schneider 《Journal of magnetism and magnetic materials》2009,321(9):1182-1187
Heusler alloys are considered as interesting ferromagnetic electrode materials for magnetic tunnel junctions, because of their high spin polarization. We, therefore, investigated the micromagnetic properties in a prototypical thin film system comprising two different Heusler phases Co2MnSi (CMS) and Co2FeSi (CFS) separated by a MgO barrier. The magnetic microstructure was investigated by X-ray photoemission electron microscopy (XPEEM). We find a strong influence of the Heusler phase formation process on the magnetic domain patterns. SiO2/V/CMS/MgO/CFS and SiO2/V/CFS/MgO/CMS trilayer structures exhibit a strikingly different magnetic behavior, which is due to pinhole coupling through the MgO barrier and a strong thickness dependence of the magnetic ordering in Co2MnSi. 相似文献
18.
《Solid State Ionics》1986,21(2):97-115
The relations between the orientational disorder of SiO4(PO4) tetrahedra and fast sodium diffusion in superionic NASICON have been studied by conductivity (complex impedance method), DSC, X-ray powder difraction and vibrational spectroscopy (IR and Raman). Sol-gel routes allow to obtain pure glassy NASICON (Na1+xZr2SixP3-xO12x≅2) in the 500−700°C temperature range. Tetragonal zirconia nucleates above 700°C and disappears at about 900°C when the isolated tetrahedra framework is formed: a high orientational static disorder of tetrahedra exists and the symmetry is rhombohedral at all studied temperatures (20−600 K). Thermal treatment above 1100°C induces a drastic decrease of the static orientational disorder and nucleation of monoclinic zirconia. The resulting compound exhibits a monoclinic symmetry at R.T. and three phase transitions, two diffuse at about 60 K and 520 K and the 423 K monoclinic-rhombohedral transition associated with the superionic conducting state. An increase in dynamic disorder (broad Rayleigh wing up to 500 cm-1 is simultaneously observed. The lower the static disorder at low temperature, the higher the dynamic orientational disorder and the phase transitions, and the lower the activation energy of conductivity at high temperature. 相似文献
19.
Optical absorption in MnIn2S4 single crystals has been studied. Direct and indirect optical transitions are found to occur at photon energies of 1.90?C2.16 eV in the temperature range of 80?C342 K. The temperature dependence of the band gap is determined; its temperature coefficients E gd and E gi are found to be ?4.84 × 10?4 and ?6.33 × 10?4 eV/K, respectively. The electron-phonon interaction is the main mechanism of the temperature shift of the intrinsic-absorption edge. MnIn2S4 single crystals exhibit anisotropy in polarized light at the absorption edge in the temperature range of 90?C190 K; the nature of this anisotropy is explained. 相似文献
20.
The polyamorphism of liquid silica (SiO2) at 3200?K and in a wide pressure range is investigated by molecular dynamics simulation. Results show that the structure of liquid SiO2 consists of five order-parameters that do not depend on compression. Three order parameters that relate to the short-range order are SiOx coordination units (x?=?4, 5, 6) and two order parameters that relate to the intermediate-range order are OSi2 and OSi3 linkages. The structure of liquid silica under compression can be described by the two-state model: low-density and high-density states. The low-density state is formed by clustering of OSi2 linkages (in the low-density state, the short-range order (SRO) is mainly characterized by SiO4 coordination units), conversely, clustering of OSi3 linkages will form high-density state (in the high-density state, the SRO is mainly characterized by SiO5 and SiO6 coordination units). Under compression, in the liquid silica co-exist two phases: low-density and high-density phases. The size of phase regions significantly depends on compression. 相似文献