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1.
In this article, we provide a detailed mathematical analysis of the Helmholtz equation, in the context of dynamical wide-angle X-ray scattering by deformed crystals. We show that the dynamical theory of diffraction may be written without introducing a sophisticated dispersion theory, by using the following simple condition for wavevectors: |Kh|=|K0|=k. This choice gives simple way to describe the reciprocal space mapping phenomena in a dynamical approach and simulate the diffraction curves for strained crystals over many orders of reflection. Several theoretical approaches to obtaining the angular distribution of scattered intensity are discussed.  相似文献   

2.
Neodymium-substituted bismuth titanate (Bi3.25Nd0.75Ti3O12, BNT0.75) ceramics was prepared by chemical co-precipitation along with calcinations. The lattice instability has been investigated by variable-temperature Raman scattering and X-ray diffraction. The results showed that there was an orthorhombic to pseudo-tetragonal phase transition at about 695 K, in terms of the evolution of temperature dependence of Raman scattering frequencies. Some changes at about 695 K in the XRD lines, the lattice parameters (a, b, and c) as well as the orthorhombic distortion b/a have been detected in the high temperature X-ray diffraction, which confirmed the conclusion that the BNT0.75 ceramics undergoes a ferroelectric to paraelectric phase transition at about 695 K.  相似文献   

3.
The lattice parameters of Al3BC have been measured up to 5 GPa at ambient temperature using energy-dispersive X-ray powder diffraction with synchrotron radiation. A fit to the experimental p-V data using Birch-Murnaghan equation of state gives values of the Al3BC bulk modulus 116(4) GPa and its first pressure derivative 9(2). In the 1.6-4.8 GPa range at temperatures above 1700 K Al3BC undergoes incongruent melting that results in the formation of Al3BC3, AlB2 and liquid aluminum.  相似文献   

4.
The amount of InN included in InGaN films grown by MOCVD (metalorganic chemical vapor deposition) was estimated by X-ray diffraction measurement technology. The In compositions in our InGaN films are measured as 0.1–0.34 by X-ray 2θ scan using Vegard’s law. The inclusion of InN in InGaN layers was obtained as 0.0684–2.6396% by measuring the ratio of the integrated intensity of the InN (0002) peak to that of the InGaN (0002) peak in X-ray rocking curves. The theoretical diffraction intensities from InN and InGaN have been calculated according to the X-ray-diffraction theory. The values of the InN inclusion for all our samples were less than 3%, which indicated that the degree of phase separation of the samples was low. It was also found that the flow rate of N2 carrier gas and the operation pressure strongly affected the InN inclusion in InGaN. Received: 20 November 2000 / Accepted: 16 May 2001 / Published online: 27 June 2001  相似文献   

5.
We have performed a detailed X-ray diffraction study of O2 adsorbed on UCAR-ZYX and Le Carbon Lorraine vermicular exfoliated graphite between 15 and 50 K. At least four phases of physisorbed oxygen are found. The monolayer δ phase consists of a centered parallelogram lattice, with the molecular axes parallel to the graphite surface. The data are consistent with a triple point at 26 K. The melting transition at a coverage of one monolayer appears to be first order. At higher coverages the molecules undergo a lying-down to standing-up transition; the higher coverage ζ phase froms an approximately triangular lattice with the molecular axes perpendicular to the graphite surface. Satellite peaks around the (1, 0) Bragg peak indicate, however, that this cannot be a simple triangular lattice; possible explanations include successively incommensurate layers or a sinusoidal density modulation. For coverages in the two-layer region the ζ phase modulation peaks disappear at 37 K, and at 40 K the adsorbed oxygen appears to undergo a first order melting transition into a fluid phase. With increasing coverage, the 2D X-ray diffraction profiles and phase boundaries do not connect smoothly onto those of the 3D α and β phases. At low temperatures (T < 30 K) the ζ phase always coexists with bulk crystallites; for temperatures near the 2D melting transition the 3D peaks are not observable. These data, taken together with the heat capacity results, suggest a wetting transition with only the bilayer lamellar phase or bulk O2 being stable at low temperatures.  相似文献   

6.
High-resolution X-ray diffraction is used to obtain the strain profile of a wide range of epitaxial semiconductor samples. The samples are divided into five categories: Strained layers on a substrate, (partly) relaxed layers on a substrate, strained-layer superlattice structures, multiple relaxed layers and relaxed superlattice structures and ionimplanted samples. For each category a measurement strategy and analysis method is given. Representative examples for each category are shown.  相似文献   

7.
We have analyzed the mechanism of melting of layers adsorbed in cylindrical pores of porous materials. The goal was to understand the melting mechanism of simple fluids adsorbed in pores with heterogeneous wall surface. The studied system was a monolayer of methane molecules adsorbed in MCM-41 pore of diameter d = 4 nm. Both experimental (neutron scattering) and simulation (Monte Carlo) results proved extremely strong influence of the wall roughness on the melting mechanism. The most striking difference between melting on smooth and rough surfaces was in the temperatures of the transition. The transformation between solid-like and liquid-like monolayer phases adsorbed on a rough surface was observed in a very large temperature range and the solid like properties were observed even above the bulk methane melting temperature.  相似文献   

8.
Crystalline Au2O3 was obtained by hydrothermal synthesis at 3000 atm and its extended X-ray absorption fine-structure (EXAFS) at the Au L3-edge was measured at room temperature. A detailed full multiple scattering (MS) analysis using FEFF8 theory shows that only a small number of scattering paths contribute significantly to the EXAFS of Au2O3. Because of the complex unit cell (low local symmetry) of the Au2O3 structure, contributions of MS paths are almost negligible. The results indicate that FEFF8 theory provides a good reference for the analysis of Au-O phases.  相似文献   

9.
A displacive, 2nd order structural phase transition at T s = 395 K from space group I 2 m below T s to I 4/m c m above T s has been discovered in the two-dimensional spin dimer compound SrCu2(BO3)2. The temperature evolution of the structure in both phases has been studied by X-ray diffraction and Raman scattering, supplemented by differential scanning calorimetry and SQUID magnetometry. The implications of this transition and of the observed phonon anomalies in Raman scattering for spin-phonon and interlayer coupling in this quantum spin system will be discussed. Received 24 July 2000 and Received in final form 2 November 2000  相似文献   

10.
The fulleride salt C60-tetraphenylphosphonium bromide is investigated as a function of temperature by single crystal X-ray diffuse scattering and diffraction. At room temperature, the C60 orientational disorder is found to be more complex than previously expected. Moreover, a structural phase transition, due to the C60 orientational ordering, is evidenced around 120 K. Its relation with the stabilization of a static Jahn-Teller effect is discussed. Received 3 November 1999  相似文献   

11.
Sn-filled CoSb3 skutterudite compounds were synthesized by the induction melting process. Formation of a single δ-phase of the synthesized materials was confirmed by X-ray diffraction analysis. The temperature dependences of the Seebeck coefficient, electrical resistivity and thermal conductivity were examined in the temperature range of 300-700 K. Positive Seebeck and Hall coefficients confirmed p-type conductivity. Electrical resistivity increased with increasing temperature, which shows that the Sn-filled CoSb3 skutterudite is a degenerate semiconductor. The thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. The lowest thermal conductivity was achieved in the composition of Sn0.25Co8Sb24.  相似文献   

12.
In this paper we describe an approach for the formation of composite layers on the surface of refractory metals. We show that laser radiation on refractory metals (Ti, V, Zr, Mo, Hf, Ta, and W) immersed in liquid nitrogen can provide a chemical synthesis of nitride phases on the surface of metals. The metals were subjected to pulsed laser radiation with a wavelength of 1.06 μm. The power density ranged from 104 to 109 W cm−2. The synthesis of nitrides began with the formation of MexNy (x > y) phases with low contents of nitrogen. When the melting point was reached at the metal surface, the quantity of MeN phases increased sharply. Study of the melting zone showed that it contained a non-uniform distribution of nitride phases. The quantity of nitrides was a maximum on the surface and decreased with the increase of the depth of melting zone. Due to the high-cooling rates, titanium nitride crystallized in the form of columns. Maximum microhardness in the Ti surface layer was up to 20,000 MPa.  相似文献   

13.
Using small-angle X-ray scattering, the repeat distance vs. temperature is measured for a homologous series of multilamellar vesicles of lecithins with varying acyl chain length in excess water condition around the lipid main transition. A systematic chain length dependence is found which is in accordance with a bending rigidity renormalization and critical unbinding of the lamellae close to the transition, as previously suggested in H?nger et al. [Phys. Rev. Lett. 72, 3911 (1994)]. Received 13 January 1999 and Received in final form 6 September 1999  相似文献   

14.
Double-period [(Pt 1.7 nm/Fe 0.9 nm)5Fe(tFe2)]8 and [(Pt 1.8 nm/Fe 0.6 nm)5Fe(tFe2)]8 multilayers with different thickness tFe2 (between 0.23 and 4.32 nm) of the additional Fe layers, prepared by combinatorial sputter deposition, show differences in the mosaic spread and the vertical interfacial roughness when deposited on native or thermally oxidised Si wafers. Simulations of the wide-angle X-ray scattering intensities revealed the presence of interdiffusion in the (Pt/Fe)5 bilayers and systematic variations of the grain sizes, perpendicular to the film surface, as well as the rms variations of the two superlattice periods with the total film thickness. A comparison of ω-rocking scans shows an increase of the correlated vertical roughness of the (Pt/Fe)5 multilayers with the total multilayer thickness.  相似文献   

15.
The thermodynamics and structure of the surface adsorbed phase in binary C15-C16 and C15-C17 n-alkane mixtures confined in graphite pores have been studied by differential scanning calorimetry and small-angle X-ray scattering. The previously observed selective adsorption of the longer alkane for chain length differences greater than five carbon atoms is verified but reduced for chain length differences less than or equal to two. With a difference in chain length of one carbon atom, Vegard's law is followed for the melting points of the adsorbed mixture and the (0 2) d-spacing is a continuous function of the mole fraction x. With a two-carbon atom difference, samples aged for 1 week have a lamellar structure for which the entities A1−xBx try to be commensurate with the substrate. The same samples aged for 1 month show a continuous parabolic x-dependence for both the melting points and the d-spacings. An explanation in terms of selective probability of adsorption is proposed based on crystallographic considerations.  相似文献   

16.
The structure and morphology of chromium disilicide (CrSi2) nanometric films grown on 〈1 0 0〉 silicon substrates both at room temperature (RT) and at 740 K by pulsed laser ablation are reported. A pure CrSi2 crystal target was ablated with a KrF excimer laser in vacuum (∼3 × 10−5 Pa). Morphological and structural properties of the deposited films were investigated using Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GID), X-ray reflectivity (XRR), scanning (SEM) and transmission electron microscopy (TEM). From RBS analysis, the films’ thickness resulted of ∼40 nm. This value is in agreement with the value obtained from XRR and TEM analysis (∼42 and ∼38 nm, respectively). The films’ composition, as inferred from Rutherford Universal Manipulation Program simulation of experimental spectra, is close to stoichiometric CrSi2. GID analysis showed that the film deposited at 740 K is composed only by the CrSi2 phase. The RT deposited sample is amorphous, while GID and TEM analyses evidenced that the film deposited at 740 K is poorly crystallised. The RT deposited film exhibited a metallic behaviour, while that one deposited at 740 K showed a semiconductor behaviour down to 227 K.  相似文献   

17.
We present a synchrotron X-ray diffraction study of pressure-induced changes in nanocrystalline anatase (with a crystallite size of 30-40 nm) to 35 GPa. The nanoanatase was observed to a pressure above 20 GPa. Direct transformation to the baddeleyite-TiO2 polymorph was seen at 18 GPa. A fit of the pressure versus volume data to a Birch-Murnaghan equation yielded the following parameters: zero-pressure volume, V0=136.15 Å3, bulk modulus, KT=243(3) GPa, and the pressure derivative of bulk modulus, K′=4 (fixed). The bulk modulus value obtained for the nanocrystalline anatase is about 35% larger than that of the macrocrystalline counterpart.  相似文献   

18.
In this work we present a structural analysis of La0.75Sr0.25MnO3/LaNiO3 (LSMO/LNO) superlattices, performed by X-ray diffraction spectroscopy and X-ray reflectivity. The samples were deposited by dc magnetron sputtering on single-crystalline (0 0 1) oriented SrTiO3. The strain relaxation and the roughness at the interfaces were estimated from the analysis of the X-ray patterns. The thickness of LSMO reference layers has been measured by means of low-angle X-ray reflectivity, finding a very good agreement with the nominal values.  相似文献   

19.
High-quality thin Fe films were deposited on MgO(001) and Al2O3(1120) substrates in the thickness range from 7 to 50 nm. The structural properties have been studied by out-of-plane and in-plane X-ray scattering experiments. From the out-of-plane measurements the electron density profile was determined together with interface and surface roughness parameters. Fe on Al2O3 grows along the [110]-direction with a structural coherence length comprising about the total film thick ness and a very small mosaicity. From in-plane scattering experiments a three-domain structure was observed. On MgO(001) substrates Fe grows in the [001]-direction, with the Fe [100]-axis parallel to the MgO [110]-axis. On both substrates, the Fe films exhibit a very small surface and interface roughness, indicative for a high quality of the sputtered samples.  相似文献   

20.
用掠入射X射线衍射法观察到钛酸铅多晶铁电薄膜表面层与体内的相变温度不同,表面层的结构参数也有异于体内;唯象地把多晶铁电薄膜抽象为一个表面层为细晶粒、低应变层,体内为粗晶粒、高应变层的两层结构,根据应力和晶粒尺寸效应对铁电相变的影响,解释了钛酸铅多晶铁电薄膜的相变特征 关键词:  相似文献   

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