Superconducting properties of very high quality NbN thin films grown by pulsed laser deposition

In this work, we study the effect of the various substrates on the growth and superconducting properties of NbN thin films grown by using pulsed laser ablation in a N2 + 1%H2 atmosphere on MgO, Al2O3 and Si substrates. Structural and superconducting analyses of the films demonstrate that using MgO and Al2O3 substrates can significantly improve the film properties compared to Si substrate. The X-ray diffraction data indicate that MgO and Al2O3 substrates produce highly oriented superconducting NbN films with large coherent domain size in the out-of plane direction on the order of layer thickness and with a superconducting transition temperature of 13.1 K and 15.2 K, respectively. On the other hand, the NbN film grown on the Si substrate exhibits random polycrystalline orientation. Together with the smallest coherent domain size it leads to the lower critical temperature of 8.3 K. Finally, by using a passivation surface layer we are able to improve superconducting properties of NbN thin film and we observe superconducting transition temperature 16.6 K, the one of the highest value reported so far for 50 nm thick NbN film on sapphire.

Combined texture and microstructure analysis of deformed crystals by high-energy X-ray diffraction

It is shown that high-energy X-ray diffraction allows a fast and accurate texture and microstructure analysis of crystals, which can help to set up optimal industrial procedures for materials manufacturing. This paper presents the experimental and theoretical aspects of quantitative texture analysis using high-energy synchrotron beams. Intensity corrections are less important in this approach than in classical laboratory methods; however, the most important correction, related to the Lorentz factor, can introduce relative fraction changes of up to about 40% compared to the uncorrected case. The resolution of the orientation density function also influences the results. For example, the usual 5° resolution leads to relative deviations of up to 30% in the fraction of some components. The method allowed detection of small changes taking place during the recovery and continuous recrystallization of a cold-rolled Al–TiB2 nanocomposite. Texture information was combined with the results of line profile analysis, evidencing the evolution of the average dislocation density and coherent domain size of the selected grain families. It was found that recovery, as described in terms of dislocation annihilation and coherent domain coarsening, takes place at similar rates in all components.

Microstructure and Residual Stress in T40 Titanium after Tensile Test

The goal work of this work is to describe the qualitative and quantitative behaviour of titanium T40 during tensile test. Material characteristics were determined using EBSD and X-ray techniques. Textures, twin boundary fractions, residual stresses and coherent domain size were determined. It was found that deformation mechanisms and microstructure characteristics are different in the samples stretched along rolling and transverse directions. For example the average grain size, as determined from EBSD measurements, is higher in the sample stretched along rolling direction. Also smaller coherent domains form and residual stress is more easily relaxed in this sample. A strong appearance of tensile twins was observed in the samples deformed along transverse direction. In the present paper a complex study of material characteristics and deformation mechanisms is presented. A special emphasis is done on residual stress characteristics determined in the samples stretched in two perpendicular directions.

Investigation Of Helium Implanted Fe–Cr Alloys By Means Of X–Ray Diffraction And Positron Annihilation Spectroscopy

X-ray diffraction (XRD) and positron annihilation spectroscopy (PAS) have been used for the characterization of the two binary alloys Fe-Cr with Cr content 2.36 and 8.39 wt%. The influence of ion implantation on these alloys was studied. Different implantation doses of helium, up to 0.5 C/cm2, were used to simulate neutron-induced damage in a sub-surface region. To characterize the damage, a lattice parameter, coherent domain size, residual stress and a crystallographic texture have been studied by grazing incidence X-ray diffraction (GIXRD). It was found out that these parameters showed a similar dependence on the implantation dose as the positron lifetime determined by positron annihilation spectroscopy.

Distribution of Dislocation Density in Tubes from Zr-Based Alloys by X-Ray Data

As applied to tubes from Zr-based alloys, the X-ray method was developed to determine the dislocation density distribution in a-Zr depending on the orientation of Burgers vector. The method consists in registration of X-ray line profiles by each successive position of the sample in the course of diffractometric texture measurement using reflections of two orders, the following determination of coherent domain size and lattice distortion by means of the Warren-Averbach method for each orientation of reflecting planes, separate calculation of the density of c- and a-dislocations with all possible orientations of Burgers vector and presentation of results in generalized pole figures. Obtained data testify that the dislocation density varies within very wide intervals of several orders of magnitude depending on the grain orientation both in as-rolled and annealed tubes. Features of the constructed dislocation distributions are closely related to the crystallographic texture of studied tubes.

Inhomogeneous Distribution of Dislocation Density as Manifestation of Multiscale Structure in Tubes from Zr - Based Alloys

An X-ray method was developed to determine the dislocation density in metal materials as a distribution depending on the orientation of Burgers vector. The method includes registration of X-ray line profiles by each successive position of the sample in the course of diffractometric texture measurement using reflections of two orders, the following determination of coherent domain size and lattice distortion by means of the Warren-Averbach method for each orientation of reflecting planes, separate calculation of the density of c- and a-dislocations with all possible orientations of Burgers vector and presentation of results in the generalized pole figures. The method was used to determine the dislocation density in tubes of Zr-based alloys for nuclear industry. Obtained data show, that the dislocation density varies within very wide interval of several orders of magnitude depending on the grain orientation both in as-rolled and annealed tubes. Features of the dislocation distribution in tubes are closely related to their crystallographic texture.

The dislocation model of strain anisotropy in whole powder-pattern fitting: the case of an Li–Mn cubic spinel

Anisotropic strain broadening in X-ray or neutron powder diffraction can cause severe difficulties in whole powder-pattern fitting and Rietveld structure refinement. Several phenomenological models have been proposed to deal with this problem. These, however, lack physically sound bases. In the present work the dislocation-based model of strain anisotropy is applied in the Fourier formalism of profile fitting. It is shown that the anisotropic contrast of dislocations can fully account for strain anisotropy. A few physically sound parameters, namely the average dislocation density, the average coherent domain size, the dislocation arrangement parameter and the dislocation contrast factors, enable a perfect profile fitting to the powder pattern of a cubic Li–Mn spinel obtained at the Daresbury synchrotron storage ring.