Papers by Keyword: Diffuse Scattering

Abstract: The results of the experimental study of the critical X-ray scattering (CS) in PbZr_0.6Ti_0.4O₃ (PZT40) single-crystal are presented. Temperature evolution of the CS lineshape and intensity was analyzed. It is demonstrated that CS can be described in terms of the mean-field model. Temperature dependences of the peak intensity of the CS, proportional to the static susceptibility, and the correlation length of the «ferroelectric fluctuations» follow the Curie-Weiss law with the Curie temperature T_c=638 K. Obtained results confirm the second-order character of the phase transition in the PZT40.

Abstract: The new technique of atomic-scale X-ray Photon Correlation Spectroscopy (aXPCS) makesuse of a coherent X-ray beam to study the dynamics of various processes in condensed matter systems.Particularly atomistic migration mechanisms are still far from being understood in most of intermetallicalloys and in amorphous systems. Special emphasis must be given to the opportunity to measureatomistic diffusion at relatively low temperatures where such measurements were far out of reach withpreviously established methods. The importance of short-range order is demonstrated on the basis ofMonte Carlo simulations.

Abstract: We present a novel method to modulate influence of diffuse scattering in fluid cavity and reflection at boundary of pulse-echo ultrasound image. A simplified formation of ultrasound model is used to delineate it, and which is merged with modified dehaze model from principle of ultrasonic imaging, a legible fluid cavity in vascular or amniotic fluid of ultrasound image is obtained. Local and global characteristics of the image are utilized to adjust diffuse in different levels. Experimental results indicate that the proposed method is capable of producing ultrasound images that have better image quality and greater fidelity to the true tissue reflectivity.

Abstract: Results of the study of the structural and magnetic properties of periodic Fe/V heterostructures with periods D = 9.4nm and D = 6.3nm are present. The study has shown that ferromagnetic islands are formed on the interfaces of Fe and V. These islands have different magnetic properties as sub-layers of pure iron. Islands in the sample with the period D = 9.4 nm have anisotropic shape, which leads to the anisotropy of magnetic properties.

Abstract: Single crystals of Ni-25.6 at.% Pt and Ni-87.8 at.% Pt were investigated by diffuse x-ray scattering for states of thermal equilibrium (923 K and 603 K, respectively). The separated short-range order scattering showed local maxima at 100 positions. Effective pair interaction parameters, as determined by the inverse Monte Carlo method, show a strong composition dependence of the nearest-neighbor interaction parameter. First-principles calculations are consistent with this finding and reveal a large contribution due to lattice strain. Based on values of the ordering energy, NiPt₃ with L1₂ structure was considered as a plausible new intermetallic phase, with Monte Carlo simulations giving an order-disorder transition temperature of 650 K. A single crystal of Ni-75.2 at.% Pt, quenched from 1073 K and aged at 613 K, showed L1₂-type ordering, reaching a long-range order parameter of 0.50(4) after 800 h.

Abstract: We succeeded in synthesizing single crystals of a novel nickel sulfate Ni2-δSO5 by a hydrothermal method. A single-crystal X-ray diffraction revealed a tetragonal structure with lattice constants, a = 5.184 Å and c = 12.91 Å. In this structure, one-dimensional chains composed of face-shared NiO6 octahedra elongate along the a axis and the b axis alternately, constructing a ‘log-cabin’ type framework where neighbor chains lying orthogonally to each other are connected by SO4 tetrahedra. A detailed refinement of the structure suggested that the site occupancy of Ni is only 63%, corresponding to δ ≈ 2/3. Furthermore, X-ray oscillation photographs exhibit diffuse-scattering patterns probably arising from a short-range order of the Ni defects. Magnetic susceptibility revealed an antiferromagnetic transition accompanied by a weak ferromagnetism at 17 K.

Abstract: In this paper there are presented results of structure analyses of the Fe78Nb2B20 amorphous alloy after annealing. Basing on the initial analyses the “hypothetical” model structure was chosen as the combination of different kind of the Fe structure deformations: change of unit cell parameters (change of unit cell shape) and change of line broadening (change of crystallite size). The crystallite size (in meaning of the size of the ordered regions) for the amorphous state is in a range of 7 – 37 Å and for the crystalline state is about of 1100 Å. The comparison of the values of the unit cell parameters shows that the value of the basic – hypothetical unit cell in an amorphous state is bigger of 0.2 Å than in a crystalline state. After crystallisation there are detected Fe and Fe3B phases.

Abstract: Structured diffuse scattering has been observed in selected area electron diffraction patterns of PbZr1-xTixO3 (PZT). This scattering is most evident in the rhombohedral (Zr-rich) phase but has also been observed for a range of compositions including in the important morphotropic phase boundary (MPB) region as well as in the tetragonal (Ti-rich) phase. Monte Carlo computer simulation has been used to show that the scattering originates from the correlation between the displacements of cations in chains running along all four of the cubic <111>c directions. The transverse polarised nature of the scattering means that the ionic shifts are also directed along <111>c. The results are difficult to reconcile with current structural models for the low temperature phases of PZT. It is conjectured that these phases must still contain significant remnants of the disorder present in the high-temperature paraelectric cubic phase.

Abstract: Relaxation of diffuse-scattering intensities of various kinds of waves is a phenomenon of an especial interest since its study enables one to obtain the most detailed information on both the equilibrium short-range order (SRO) and the non-equilibrium SRO, and therefore, it is the most convenient instrument for investigating SRO kinetics. The SRO kinetics is studied by the use of available data of measurements of residual electrical resistivity for substitutional f.c.c.-Ni–Al solid solutions during their isothermal annealing. Within the framework of the first-order and (more realistic) second-order kinetics models, the maximum characteristic relaxation times and equilibrium magnitudes of the residual electrical resistivity for these solid solutions at different annealing (1273–1626 K) and quenching temperatures (≥ 1723 K) are evaluated, and the hypothetical values of similar quantities appropriate for the diffuse scattering of radiations are estimated too.

Abstract: Change in the R-phase transformation behavior with the increase of Fe/Co content in Ti-(50-x)Ni-xFe and Ti-(50-x)Ni-xCo alloys has been investigated through thermal property measurements and microscope observations in order to clarify the relation among the stability of the B2-type structure, premartensitic phenomena, and the R-phase transformation. It was found that with increasing Fe/Co content, the R-phase transformation behavior approaches a second-order like one. The transformation product formed very close to the second-order is composed of nanoscale domains, and its Debye temperature is low compared with the R-phase formed by obvious first-order transformation.