A. Koblischka-Veneva

Application of electron backscatter diffraction to bulk high-Tc superconductors

We have successfully obtained electron backscatter diffraction (EBSD) Kikuchi patterns on various bulk high-Tc superconductors (polycrystalline KClO3-doped and undoped YBa2Cu3O7−δ (YBCO), single crystalline YBCO and NdBa2Cu3O7−y) and on YBCO and NdBCO thin films. We have established a sample polishing procedure to obtain intense Kikuchi patterns without an additional carbon coating of the ceramic superconductors. We present Kikuchi patterns, pole figures and orientation maps of the samples. On the polycrystalline KClO3-doped YBCO samples we find two major orientations (001) and (100) normal to the sample surface, while the undoped sample does not exhibit any orientation maxima, which is ascribed to the effect of a liquid phase due to the KClO3-additive during the preparation process. Furthermore, we discuss the future possibilities for the application of the EBSD technique for growing larger, bulk melt-textured samples for applications.

Interactions of Y2BaCuO5 particles and the YBCO matrix within melt-textured YBCO samples studied by means of electron backscatter diffraction

By means of automated electron backscatter diffraction (EBSD) analysis, we studied the local orientations of embedded Y2BaCuO5(211) particles within melt-textured YBa2Cu3Ox (YBCO) samples. On both components, we obtained high-quality Kikuchi patterns, thus allowing the automated mapping of the crystal orientations and a two-phase analysis of the samples. Investigations were performed on a variety of melt-textured YBCO samples. In melt-textured YBCO with (001) orientation, we find that the embedded 211 particles do not have any preferred orientation. The EBSD maps also reveal that at certain orientations of the 211 particles the YBCO growth is not altered. From the obtained EBSD mappings, we can conclude that the formation of small 211 particles will not disturb the YBCO matrix growth, whereas the presence of large 211 particles causes severe changes in the YBCO growth, leading to the formation of subgrains. The EBSD results are presented in the form of local orientation maps and local pole figures.

Crystallographic Orientation Analyses of Magnetite Thin Films Using Electron Backscatter Diffraction (EBSD)

The crystallographic orientation of magnetite (Fe3O4) thin films was measured using electron backscatter diffraction (EBSD). Misorientation boundaries appear in maps of angular misorientation data. The distribution of misorientation angles changes after annealing the samples in air at 250degC. Most small-angle misorientations (<5deg) are removed after one minute of annealing, whereas larger misorientations (as high as 60deg) continue to persist

Misorientations in [001] magnetite thin films studied by electron backscatter diffraction and magnetic force microscopy

Magnetite thin films grown on [001] oriented MgO substrates are analyzed by means of electron backscatter diffraction (EBSD) analysis and magnetic force microscopy in applied fields. The EBSD technique enables the crystallographic orientation of individual grains to be determined with a high spatial resolution up to 20nm on such ceramic samples. A high image quality of the recorded Kikuchi patterns was achieved enabling multiphase scans and high spatial resolution measurements. Upon annealing in air, the magnetic properties of the magnetite thin films were found to change considerably. Using the EBSD analysis, we find that misoriented grains remaining after the annealing step form small islands with a size of about 100nm. The size and distribution of these islands correspond well to the observations of antiferromagnetic pinning centers within the magnetic domain structures carried out by magnetic force microscopy on the same samples.

Magneto-optical and microstructural investigations on KClO3-doped YBCO HTSC

Abstract The influence of KClO 3 addition on the magnetic properties and microstructure of YBCO HTSC materials with nominal composition (A): Y 1 Ba 2− x K x Cu 3 O y , (B): Y 1−0.2 x Ba 2−0.2 x K x Cu 3 O y , (C): Y 1 Ba 2 Cu 3.5− x K x O y ( x =0–0.75) were investigated. Magneto-optic imaging of flux distributions was employed to study the grain connectivity in the doped and undoped samples in a direct way. The obtained flux patterns taken at various temperatures reveal that KClO 3 -doped samples ( x =0.30) exhibit flux distributions being close to those being observed in melt-textured superconductors. This demonstrates that the grain connectivity in the doped samples is considerably improved as compared to pure ones, which is an important issue for the fabrication of coated conductors of YBCO.

Grain orientations and distribution of Y2Ba4CuUOx phase in melt-textured YBCO with addition of depleted uranium oxide studied by EBSD

The local grain orientations and the distribution of Y2Ba4CuUOx (U-2411) phase are measured within melt-textured YBCO samples by means of electron backscatter diffraction (EBSD). In this work, several samples with varying addition (0.1–0.8 wt%) of depleted uranium oxide (DU) were analysed by means of EBSD. The embedded U-2411 particles were found to have sizes around 200 nm, some large particles being present in the samples with a high DU concentration. Combined EBSD and EDX analysis enabled the identification of the Kikuchi patterns of the U-2411 phase, so that a true three-phase EBSD scan (YBCO, Y2BaCuO5 and U-2411) becomes possible.

Analysis of the microstructure of superconducting YBCO foams by means of AFM and EBSD

YBa2Cu3Oy (YBCO) foam samples show an open, porous foam structure, which may have benefits for many applications of high-Tc superconductors. As the basic material of these foams is a pseudo-single crystalline material with the directional growth initiated by a seed crystal similar to standard melt-textured samples, the texture of YBCO is a very important parameter. Therefore, we analysed the local texture and grain orientation of the individual struts forming the foam by means of atomic force microscopy (AFM) and electron backscatter diffraction (EBSD). Due to the processing route starting with Y2BaCuO5 (211), a two-phase analysis must be performed, so a high surface quality is necessary to enable an automated EBSD scan. Good quality Kikuchi patterns were obtained from both the YBCO and 211 phases. We found an inhomogeneous distribution of the residual 211 particles, which are mainly randomly oriented and have sizes ranging between 200 nm and 15 μm. In contrast to this, the YBCO matrix shows a dominating orientation with cracks with a typical distance of 1–10 μm. Furthermore, the analysis of strut cross-sections reveals that the entire strut is converted to the YBCO phase.

EBSD analysis of the microtexture of Ba-hexaferrite samples

The microtexture of differently prepared Ba-hexaferrite samples is investigated by means of electron backscatter diffraction (EBSD). Kikuchi patterns are obtained with a high image quality, enabling a spatial resolution of the EBSD maps of about 20 nm. The spatially highly resolved EBSD mappings provide additional information (individual grain orientation, misorientation angles, grain size distribution) as compared to the standard analysis techniques, which can contribute to an optimization of the growth process. Furthermore, as the crystallographic orientation of each grain is known, an exact analysis of the grain aspect ratio becomes possible which provides further insight to the microstructural dependence of the magnetic properties of ferrites.

Nanostripes in (Nd0.33Eu0.28Gd0.38)Ba2Cu3Ox superconductors

Nanostripes are observed in melt-textured, Gd-enriched light-rare-earth (LRE)-based ternary (Nd0.33Eu0.28Gd0.38)Ba2Cu3Ox (NEG-38) superconductors. Employing atomic force microscopy/scanning tunneling microscopy topographic scans together with electron backscatter diffraction (EBSD) analysis, the authors determine the direction of the nanostripes with respect to the twin structure. Details of the topography measurements and of the EBSD maps reveal that the nanostripes are composed of nanoclusters of the LRE-rich phase. The nanostripes in the NEG-38 samples have a periodicity of about 40–60nm, and in lateral direction between 300 and 500nm. The role of these nanostripes for flux pinning in these compounds is discussed.

Subgrain structures and superconductivity in RE–Ba–Cu–O bulk superconductors

Abstract We have studied the microstructures of subgrains in large single-domain RE–Ba–Cu–O (RE=Y, Nd, Sm) bulk superconductors through microscopic observation and microarea X-ray pole figure analyses. The misorientation angle of subgrains increases as the crystal growth proceeds, and thus more crystal defects such as dislocations are seen at the later stage of the growth. Electron backscatter diffraction technique was successfully utilized for characterizing the subgrain boundaries. Electric and magnetic measurements for several samples containing different subgrain geometries have been performed. The results of I – V and resistivity measurements indicated that subgrains act as weak-links especially in a high magnetic field region.