Temperature dependence of the X-ray diffuse scattering intensity in V3Si in the temperature range from 8 to 300 K

Measurements of the diffuse X-ray scattering are performed from the (110) plane in V₃Si single crystal at different temperatures from 300 to 8 K. Contours of equal diffuse scattering intensity are drawn over the 440 node in the (001) and (111) sections. The temperature dependence and the anisotropy of the thermal diffuse scattering intensity distribution for this compound are analysed.     

Effects of structure instability of a V3Si single crystal from X-ray scattering data

Diffuse X-ray scattering from a V₃Si single crystal was studied at room temperature. It was demonstrated that the structure possesses instability regions associated with the formation of a new phase. The characteristic features of the q dependence of diffuse scattering are indicative of the presence of two-types of domains— those randomly distributed over the crystal and those forming a spatially periodic distribution.     

An inelastic X-ray scattering study on the collective dynamics in the ‘non-simple’ liquid metal Si

The dynamic structure factor S(Q,ω) of liquid silicon has been measured using inelastic X-ray scattering. The data show that distinct longitudinal collective modes exist in this ‘non-simple’ liquid metal similar as in the so-called ‘simple’ metallic fluids as, e.g. the liquid alkalis. However, the Si-modes are considerably more strongly damped and in S(Q,ω) the corresponding excitation peaks cease to exist for momentum transfers of about half the structure factor maximum position. The degree of positive dispersion, in the Q-ω-relation of the modes is, however, similar as in the liquid alkalis, indicating that the microscopic viscosity is similar in l-Si and that the stronger damping may rather be related to the higher thermal diffusivity. Additionally, it is found that the shape of the quasielastic line close to the structure factor maximum deviates considerably from the shape found in simple liquid metals. This observation is related to the onset of short time correlations between colliding particles on the sub picosecond scale which is in accord with findings from ab initio computer simulations under similar conditions.     

The structural response of BCC Fe lattice loaded in [110] direction

The structural response of BCC Fe lattice loaded in [110] direction has been investigated with MAEAM. The results show that, even if an orthorhombic path (b₂≠b₃) is applied, the deformation is spontaneous along the tetragonal path (b₂≡b₃) while b₁ is less than 0.3449nm in compressive region. In addition to the initial BCC phase, a BCT phase and the other BCC phase appear also at stress‐free states. The BCT phase with the local maximum internal energy of ‐4.227eV is unstable and would slip spontaneously into the appeared BCC phase with the same minimum internal energy of ‐4.280eV as the initial BCC phase. The stable region ranges from ‐43.87eV/nm³ to 44.06eV/nm³ in the theoretical strength or from ‐7.34% to 6.49% in the strain correspondingly. Furthermore, the relations B₁₁=B₂₂, B₁₃=B₂₃ and B₄₄=B₅₅ occur at the initial state. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Acoustic damping in Li2O–2B2O3 glass observed by inelastic X-ray and optical Brillouin scattering

The dynamic structure factor of lithium-diborate glass has been measured at several values of the momentum transfer Q using high resolution inelastic X-ray scattering. Much attention has been devoted to the low-Q-range, below the observed Ioffe–Regel crossover q_IR ≃ 2.1 nm⁻¹. We find that below q_IR, the linewidth of longitudinal acoustic waves increases with a high power of either Q, or of the frequency Ω, up to the crossover frequency Ω_IR ≃ 9 meV that nearly coincides with the center of the boson peak. This new finding strongly supports the view that resonance and hybridization of acoustic waves with a distribution of rather local low frequency modes forming the boson peak is responsible for the end of acoustic branches in strong covalent glasses. Further, we present high resolution Brillouin light-scattering data obtained at much lower frequencies on the same sample. These clearly rule out a simple Ω²-dependence of the acoustic damping over the entire frequency range.     

Diffuse X-ray scattering study of the temperature variation of elastic constants in indium arsenide

The elastic constants of indium arsenide have been determined in the temperature range from 80 to 750 K on n-type samples with a carrier concentration of about 8 · 10¹⁷ cm⁻³ by Wooster's method from the measurements of the thermal X-ray diffuse scattering intensities. An average decrease in the elastic constants with increasing temperature over the above mentioned temperature range is found to be about 8%.     

High-resolution inelastic X-ray scattering measurements of an Al72Pd20Mn8 alloy above the melting point

The dynamic structure factor S(Q, ω) of the melt of an icosahedral quasicrystal, Al₇₂Pd₂₀Mn₈, was measured at 1223 K near the melting point, T_m = 1140 K, for momentum transfers, Q, from 1.5 nm⁻¹ to 5.55 nm⁻¹ by means of inelastic X-ray scattering technique using synchrotron radiation at SPring-8. The composition of Al₇₂Pd₂₀Mn₈ is a special one in AlPdMn ternary alloys, since icosahedral AlPdMn quasicrystal is formed directly from the melt. The acoustic mode was observed in the low Q region, and a sound velocity was estimated to be 4170 ± 100 m/s.     

On Unstable Directions of Dislocations in the Intermetallic Compound V3Si

The angular dependence of the reciprocal elastic energy of a straight dislocation in the superconductor V₃Si has been computed for different temperatures and slip systems taking elastic anisotropy into account. Regions of instability have been found which depend on temperature. Crystallographic slip planes may be unstable against climb.     

X-ray mapping in heterocyclic design: V. Diffractometric study of the crystal structure of 2-hydroxy-3-trifluoracetylimidazo[1,2-a]pyridine hydrochloride at 180 K

The crystal structure of 2-hydroxy-3-trifluoracetylimidazo[1,2-a]pyridine hydrochloride C₉H₆F₃ClN₂O₂ is determined by X-ray diffraction at 180 K. The structure is solved by the direct method and refined by the least-squares procedure to R = 0.0296. The alternation of bond lengths in the six-membered fragment of the molecule is observed. One of the specific features of the crystal structure is the formation of a system of the N-H?Cl^? (N?Cl, 3.09 Å; N-H, 0.83 Å; H?Cl, 2.33 Å; and N-H?Cl, 153°) and O-H?Cl^? (O?Cl, 2.87 Å; O-H, 0.95 Å; H?Cl, 1.92 Å; and O-H?Cl, 178°) hydrogen bonds in which the chlorine atoms are related to the reference atom by different symmetry transformations.     

Study of the microdynamics of liquid lithium and lithium-hydrogen melt by inelastic neutron scattering

The frequency spectra of vibrations of Li atoms at temperatures of 22, 227, 397, and 557°C and the lithium-hydrogen melt (98 at % ⁷Li, 2 at % H) at 557°C have been obtained from the experimental neutron inelastic scattering data. On the basis of the frequency spectra, the temperature dependences of the mean-square displacement of Li atoms, the mean-square amplitudes of atomic vibrations, and the velocity autocorrelation function of atoms have been calculated. The speed of sound in liquid lithium has been estimated within the Debye model. The frequency spectra of lithium-hydrogen melt and solid lithium hydride are compared. A generalized frequency spectrum of vibrations of hydrogen atoms in lithium-hydrogen melt is obtained.     

Stress relaxation in the intermetallic phase V3Si at elevated temperatures

The plastic deformation behaviour of the intermetallic phase V₃Si (Cr₃Si-type) was investigated in stress relaxation experiments. The experiments revealed that V₃Si shows stress relaxation after dynamic deformation above 1550 K. The characteristic parameters of stress relaxation depend strongly on temperature, chemical composition (within the range of homogeneity) and deformation rate. The decrease of stress is governed by dislocation climb processes.     

Trimethylamine-N-oxide induced disproportionation of Re2(CO)10: Synthesis and X-ray crystal structure of [fac-Re(CO)3(ONMe3)3] [ReO4]

An attempted synthesis of [Re(CO₃) (-OH)]₄,1, by reacting Re₂(CO)₁₀ with an excess of NMe₃O in THF resulted instead in isolation of a disproportionation product, [fac-Re(CO)₃(ONMe₃)₃][ReO₄],2. The structure of2 was determined via X-ray crystallography: tri-clinic,P1^¯,a=9.499(5),b=9.841(2),c=13.448(2)Å,=109.92(2),=106.89(3), =93.15(4)°,D _calc=2.22 g^–3 andZ=2. Least-squares refinement based on 1606 observed (I>3(I)) reflections gave final values ofR=0.040 andR _w=0.047. The cation is a distorted octahedron that exhibits several structural manifestations of steric crowding among the bulky NMe₃O ligands.     

Growth of YBa2Cu3O7 films with [110] tilt of CuO planes to surface on SrTiO3 crystals

YBa₂Cu₃O₇ films with the CuO plane tilted to the surface have been grown on SrTiO₃ crystalline substrates by pulsed laser deposition. This tilt was obtained by rotating the film lattice with respect to the substrate surface around its [110] axis oriented parallel to the surface. The zero tilt of the CuO plane was implemented at the orientation of the SrTiO₃ crystal surface parallel to the (100) plane. The rotation angles were varied in the range from 0° to 70°. It is found that, being tilted at any angle, the CuO planes of the film remain parallel to one or several crystallographic planes of the (100)-type substrate. In the range of tilt angles from 0° to 49°, the film has a single-crystal structure. Above 49° the film is transformed into a three-domain texture and its surface roughness sharply increases.     

Ether cleavage of [2.2.2]cryptand: synthesis and X-ray crystal structure of [NH(CH2CH2I)3][I5]

Treatment of [2.2.2]cryptand1 in toluene with HI(g) has resulted in the formation of a twophase liquid clathrate solution from which the complex [NH(CH₂CH₂I)₃][I₅]2 has been isolated and crystallographically characterized. Crystal data for2: triclinic, space group $P\bar 1$ ,a=9.301(3) Å,b=10.419(3) Å,c=11.078(3) Å, α=90.20(2)^o, β=103.28(2)^o γ=96.50(2)^o,D _c =3.57g/cm³,Z=2,R _f =0.054,R _w =0.054. The salt is a product of an ether cleavage of the macrobicycle. The crystal structure of2 contains [NH(CH₂CH₂I)₃]⁺ ions and zigzag chains of [I₅]^? ions which self-assemble to form alternating layers, of cations and anions.     

Structural characterization of Si1 − x Gex ultrathin quantum wells in a Si matrix by high-resolution X-ray diffraction

The structural characteristics of silicon samples containing one and two Si_{1 ? x} Ge_x/Si quantum wells 1.8 to 15 nm thick were determined by high-resolution X-ray diffraction. A detailed analysis of X-ray rocking curves made it possible to reproduce the Ge-concentration profiles in the quantum wells. The diffusion of germanium (up to 20%) into interface layers was observed, with a consequent broadening of the quantum well interfaces.     

Study on the influence of isotope exchange of hydrogen with deuterium on the vibrational spectrum of lysozyme by inelastic neutron scattering

The influence of isotope exchange of hydrogen with deuterium on the lysozyme dynamics was studied by incoherent inelastic neutron scattering. The generalized vibrational densities of states G(ω) were constructed from experimental results for protonated and deuterated protein samples at 200, 280, and 311 K. The major isotope effect was observed in G(ω) in the frequency region higher than 100 cm^?1. At all temperatures, both the Debye mode and the region of G(ω), whose spectral dimension corresponds to the fracton mode, are observed in the low-frequency region of the densities of states of both protonated and deuterated lysozyme. The influence of the hydrogen isotope exchange on the low-frequency region of G(ω) is insignificant.     

X-ray Studies on the Liquid Crystalline Phases of the 4-[4-n-Heptyloxy-Benzylidene-Amino]4'-cyanobiphenyl

By means of X-ray diffraction studies of oriented and non-oriented samples the lattice parameters of the orthorhombic cell of the S_E phase as well as of the hexagonal cell of the S_B phase were determined. By packing considerations a bimolecular building unit with oppositely arranged cyano-groups was assumed in the case of the S_E phase. The S_B phase is characterized by an ABAB sequence of the smectic layers in which the molecules are hexagonal arranged. The increasing mobility of the molecules at increasing temperature offers the possibility for a part of the molecules to slide in a more stable dimerized form. In the N_R and S_A phase the existence of monomers as well as of dimers is assumed. In this way a conception of the phase transitions S_E → S_B → N_R → S_A is given on the base of a decrease by steps of the dipole-dipole repulsion.     

Influence of chemical composition on dislocation structure and its change by plastic deformation of V3Si single crystals

The dislocation structure and its change by plastic deformation of V₃Si single crystals has been studied by an etch technique. The solution hardening effect established elsewhere is interpreted in terms of the observed dependence of the dislocation density ϱ(r) and its increment with the plastic deformation on the chemical composition within the range of homogeneity.