Crystal Structure and SHG Characterization of γ-BiSeO3Cl

-BiSeO₃Cl crystals were grown and characterized by x-ray microanalysis and second harmonic generation. The structure of -BiSeO₃Cl was determined by single-crystal x-ray diffraction: sp. gr. Pna2₁, a = 11.707(4) Å, b = 7.047(5) Å, c = 5.315(1) Å, Z = 4, R ₁ = 0.564, wR ₂ = 0.1272. The structures and second-order nonlinear responses of - and -BiSeO₃Cl are discussed in comparison with those of MTeO₃X (M = Bi, rare earth; X = Cl, Br, I) oxyhalides.     

Crystal Structure during Film Formation

For evaporation-deposited Ti films, face-centred cubic structure was observed at the initial stage of film growth, then transited to the hexagonal close-packed structure during film growing (less than 50 nm thick). While. for ion-beam sputter-deposited films. the structure of films always kept the fcc structure during all stages of film formation. The structure of film at initial growth stages relates with the substrate. It is discussed that different film processes and different growth stages provide different thermodynamic condition of film formation and result in the different crystal structures of films during the film formation     

Nuclear Structure and Galactic γ-Ray Activity

The observation of galactic γ lines following the decay of radioactive nuclei provides a direct link between nuclear physics experiments in earth-based laboratories and astrophysical observations with space-based observatories. Two examples are presented to illustrate this interplay: the measurement of the lifetime of ⁴⁴Ti to allow an improved determination of the ⁴⁴Ti mass of the supernova remnant Cassiopeia A from the observed γ ray activity and the measurements of excited states in ²⁴Si to determine the reaction rate of ²³Al(p, γ)²⁴Si which might be important for a reduced production of ²²Na in novae.     

Measurements of γ/γ' Lattice Misfit and γ' Volume Fraction for a Ru-containing Nickel-based Single Crystal Superalloy

A conventional X-ray diffractometer has been used to determine the γ/γ lattice misfit and γ volume fraction for a Ru-containing nickel-based single crystal superalloy at room temperature.The rocking curve was used to characterize the distribution of subgrains.The diffraction peaks obtained by ω-2θ scan were used to determine the γ/γ lattice misfit and γ volume fraction.A three peaks fitting model was proposed.The peak fitting results are in good agreement with the model.The X-ray diffraction results indicate that the nickel-based single crystal superalloy was not a perfect monocrystalline material,which is comprised of many subgrains;and each subgrain also consists of large numbers of mosaic structures.In addition,two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement.The experimental results show that the γ/γ lattice misfit and γ volume fraction will be various at the different regions of its dendritic microstructure.The average γ/γ lattice misfit and γ volume fraction of the experimental alloy are approximately-0.2% and 70%,respectively.Furthermore,the γ volume fraction calculated by atom microprobe(AP) data is also basically consistent with the experimental results.     

Structure of low temperature phase γ-LaSc3(BO3)4 crystal

We reported the investigating results of the phase transition and phase structure for LaSc₃(BO₃)₄ crystal. LaSc₃(BO₃)₄ crystal exist three phases: high temperature phase α-LaSc₃(BO₃)₄ with space group C2/c, medium temperature phase β-LaSc₃(BO₃)₄ with space group R32 and low temperature phase γ-LaSc₃(BO₃)₄ with space group Cc. Title compound γ-LaSc₃(BO₃)₄ crystallizes in the monoclinic with space group Cc, and the unit cell dimensions, a=7.740(3) Å, b=9.864(2) Å, c=12.066(5) Å, β=105.48(5)°C, V=887.8(6) Å³, Z=4, D_C=3.81 g/cm³, λ(MoKα)=0.71067 Å, F(000)=944, final R=0.040, R_W=0.054 for 1840 observed reflection with I≥3σ>(I).     

Corrosion Penetration and Crystal Structure of AA5022 in HCl Solution and Rare Earth Elements

Al-alloy (AA5022) corrosion penetration (CP) and crystal structure were investigated after running static immersion corrosion tests in 1 mol/L HCl solution and different concentrations of rare earth elements (La3+), (Ce3+) and their combination, at different temperatures. X-ray diffraction (XRD) was used to examine the surface structure before and after immersion, and secondary electron detector (SED) was operated to study surface morphology. In 1 mol/L HCI solution the corrosion penetration increased with increasing temperature and immersion time. The increase of La3+ concentrations up to 1000×10-6 g/L led to the decrease in the corrosion penetration, and the decrease in Ce3+ concentrations up to 50×10-6 g/L decreases the corrosion penetration of the alloy. Mix3 (combination of La3+ and Ce3+) dramatically reduced the corrosion penetration. This suggests that a synergistic effect exists between La3+ and Ce3+. The reaction kinetics both in absence and presence of La3+ and Ce3+ and their combination woul     

Investigation of Ge-Si Atomic Interdiffusion in Ge Nano-dots Multilayer Structure by Double Crystal X-ray Diffraction

The fluctuations of the strained layer in a superlattice or quantum well can broaden the width of satellite peaks in double crystal X-ray diffraction （DCXRD） pattern. It is found that the width of the 0^th peak is directly proportional to the fluctuation of the strained layer if the other related facts are ignored. By this method, the Ge-Si atomic interdiffusion in Ge nano-dots and wetting layers has been investigated by DCXRD. It is found that thermal annealing can activate Ge-Si atomic interdiffusion and the interdiffusion in the nano-dots area is much stronger than that in the wetting layer area. Therefore the fluctuation of the Ge layer decreases and the distribution of Ge atoms becomes homogeneous in the horizontal Ge （GeSi actually） layer, which make the width of the 0^th peak narrow after annealing.     

Effect of Crystal Structure on the Electrical Properties of CaTi1 – xFexO3 – δ

The electrical conductivity of CaTi_{1 – x} Fe _x O_{3 –} (x= 0–0.5) was measured as a function of temperature and oxygen partial pressure. At 1000°C, the highest conductivity was observed at x= 0.2. The crystal structure of the materials with x= 0, 0.2, 0.25, and 0.3 was studied by x-ray powder diffraction and refined by the full-profile analysis method. The results were used to elucidate the mechanisms of the high-temperature (1000°C) formation, ordering, and transport of oxygen vacancies in CaTiO₃upon substitution of Fe³⁺for Ti⁴⁺. The composition dependences of ionic conductivity calculated for CaTi_{1 – x} Fe _x O_{3 –} agree well with experiment.     

Several Theoretical Perspectives of Ferrite-Based Materials—Part 2: Close Packing Model for Crystal Structure

The model for crystal structure involving close packing of equivalent spheres is simple and intuitive. It is a handy tool and is familiar to material scientists. In this work, the usefulness of this model is expanded. An intuitive presentation of the structure of ferrites is developed from the close spherical packing model instead of from group theory. It is demonstrated here that the model is versatile by revealing information about structure not previously presented with this model.     

Crystal and Electronic Structure of High-Temperature Superconductive Layered Cuprates in Temperature Interval 100–300 K

For two HTSC materials, Y_1?x Ca _x Ba₂Cu₃ O _6.7 and Tl_0.8Hg_0.2Ba₂Ca₂Cu₃ O _8.15, their crystal structure has been studied earlier in the temperature interval 100–300 K. It is shown that for both compounds, the height of CuO₅ pyramids has a minimum in temperature interval from ～ 150 to ～ 250 K. The electronic structure is calculated using first principles based on the obtained data of crystal structure. It is revealed that a decrease in the CuO₅ pyramid height leads to the appearance of the electronic state density peak with an energy of 0.3–0.4 eV under Fermi level. Localized states of barium and apical oxygen make the main contribution to this peak. By reduction the temperature below ～ 150 K, these localized electronic states disappear, and under continuous cooling, the superconductivity appears.     

Combustion Synthesis, Powder Characteristics and Crystal Structure of Phases in Ce–Pr–O System

The combustion method has been employed to produce homogeneous, single phased mixed rare-earth oxides in Ce1 – xPrxO2–y system for x ranging from 0 to 0.7. A cubic fluorite structure is formed for the compositions 0 x 0.7, while for x > 0.7 mixed phases are obtained. The mixed oxides are formed at the furnace temperature of 500 °C in a short duration of 10 min. In view of the importance of these powders in catalysis, crystallite size, surface area and porosity measurements have been carried out. The crystallite size of the powders increases with x while the surface area decreases. As the temperature is increased to 850 °C, the surface area decreases and the effect is much pronounced in cerium rich oxides. The powders on calcination above 900 °C in air results in the demixing of Ce and Pr to give two fluorite phases.     

Crystal plasticity-based finite element analysis of deformation and fracture of polycrystalline lamellar γ-Tial + α2-Ti3al alloys

Deformation behavior of fully-lamellar polycrystalline -TiAl + ₂-Ti₃Al alloys has been analyzed using a finite element method. A three-dimensional rate-dependent, finite-strain, crystal-plasticity based materials constitutive model is used to represent the deformation behavior of the bulk material. The constitutive behavior of -TiAl/-TiAl lamellar interfaces and lamellae-colony boundaries, on the other hand, are modeled using a cohesive-zone formulation. The interface/boundary potentials used in this formulation are determined through the use of atomistic simulations of the interface/boundary decohesion. The constitutive relations for both the -TiAl + ₂-Ti₃Al bulk material and the lamellar interfaces and colony boundaries are implemented in the commercial finite element program Abaqus/Standard within which the material state is integrated using an Euler-backward implicit formulation. The results obtained show that plastic flow localizes into deformation bands even at an overall strain level of only 0.5% and that incompatibilities in plastic flow between the adjacent colonies can give rise to high levels of the hydrostatic stress and, in turn, to intercolony fracture. Furthermore, it is found that when lamellar interfaces are admitted into colonies, fracture is delayed and the materials fail in a more gradual manner.     

Structure of nickel-doped α-FeOOH

Colloidal particles of nickel-doped-FeOOH prepared under varied conditions were characterized using transmission electron microscopy, X-ray diffraction thermogravimetry-differential thermal analysis, Fourier transform infrared analysis, inductively coupled plasma spectroscopy and nitrogen adsorption. The unit cell dimensions of the resulting-FeOOH slightly changed on doping with nickel. Both the total and surface hydroxyl ions decreased with increasing amounts of nickel. The nickel content in the surface layer determined by X-ray photoelectron spectroscopy was larger than the total nickel content determined by inductively coupled plasma spectroscopy. The results obtained indicate that the substitution of iron with nickel took place in the surface layer more than in the internal phase.     

Relationship between Growth, Structure and Superconductivity of Single Crystal YBa2Cu3O7-δ

We study the crystal growth of YBa ₂ Cu ₃ O _7- with additives, using ac susceptibility, X-ray diffraction and STM. One specific additive, BaF ₂ , dramatically improves both the crystal growth and the superconducting properties. A cluster growth model is proposed to describe the function of the additive. F _– reduces the Al contamination of Cu-O chains, and the orthorhombicity increases. On a nanometer scale, the roughness of the chains decreases markedly. Superconductivity is further enhanced using non-contaminating crucibles. Large single crystals with T _C = 93.7 K and T _C = 0.1K were grown in Y ₂ O ₃ or BaZrO ₃ crucibles using the BaF ₂ additive.     

Influence of Crystal Orientation on the Morphology of a Single Crystal Superalloy during Directional Solidification

The solid-liquid(S/L) intedecial morphology of a single crystal superalloy DD8 has been in-vestigated. The evolutive behavior of cellular morphology with tilted preferred crystallographic orientation near cell-dendrite transition was dynamically observed, and the efFect of crystallo-graphic orientation on primary dendritic arm spacing has been examined. The experimental results show that for planar and cellular morphology no any S/L interfacial anisotropy exists,but near cell-dendrite transition, the S/L intedecial anisotropy appears and gives rise to the cellular crystal fingers tilted from thermal flow direction to preferred crystallographic orientation.The crystal fingers with their preferred orientation parallel to DS growth direction are more stable than that with tilted orientation. For the tilted fingers, the sudece on the side facing DS growth direction is less stable than that on the reverse side, the different stability on the two sides will lead to forming unsymmetrical dendritical microstructure. With the increase of tilted angle of preferred crystallographic orientation, the primary dendrite arm spacing decreases.     

Mechanical properties of γ-aluminium oxynitride

Mechanical properties have been measured of three compositionally different types of -aluminium oxynitride (Alon). The compositions corresponded to 67.5, 73 and 77.5 mol% Al₂O₃. To characterize the Alons, lattice parameters, densities, grain sizes and optical properties were measured. The measurements for the mechanical properties comprise hardness at various indentation loads, elastic properties, fracture strength and fracture toughness (at room temperature and at 600 °C).     

Surface tension of γ-TiAl-based alloys

Within the Integrated Project IMPRESS, funded by the EU, a concerted action was taken to determine the thermophysical properties of a γ-TiAl-based alloys, suitable for casting of large turbine blades for aero-engines and stationary gas turbines. The challenge was to develop a castable alloy, free of grain refiners and susceptible to heat treatment. Owing to the high reactivity of this class of alloys, many difficulties were encountered to process the liquid phase in a crucible. This prevented also the measurements of specific heat, viscosity and electrical conductivity in the liquid phase. However, surface tension and density could be measured using container-less techniques. For the surface tension determination, both the oscillating droplet method by the electromagnetic levitation as well as a combined method using two methodologies in one test (i.e. the pendant drop and sessile drop) by an advanced experimental complex that has been designed for investigations of high temperature capillarity phenomena were applied. All the quantities have been obtained as a function of temperature, in some cases also in the undercooled liquid. In this article, we report a comparative discussion on the results obtained for the surface tension of Ti–Al–Nb and Ti–Al–Ta alloys, together with the corresponding theoretical values calculated by thermodynamic models.