Abstract. A (001) SrTiO₃ wafer has been investigated in situ at room temperature under application of a static electric field of varying polarity by fluorescence x-ray absorption near edge structure (XANES) analysis at the Sr-K and Ti-K absorption edges. The XANES spectra show a clear shift of the Ti-K absorption edge energy. The shift is attributed to a change of the Ti valence state in a volume invoked by diffusion of the oxygen ions and vacancies. No shift was observed for the Sr-K absorption edge energy. Theoretical calculations support these findings.

Abstract. The volume, shape and microstructure of solids can be influenced by magnetic fields. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu₂ compounds (R = rareearth). RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magnetoic anisotropy: the strong rare-earth single ion anisotropy. Due to the pseudo-hexagonal symmetry of RCu₂, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= GiantMagnetoStrain). The variant's fraction remains unchanged when ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb_0.5Dy_0.5Cu₂. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu₂ was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. The existence of this structural irreversibility shows the potential to construct field controlled actuators or switches.

Abstract. A YNi₂B₂C single crystal containing traces of foreign phases was inspected by means of neutron and X-ray diffraction as well as scanning electron microscopy and X-ray spectroscopy methods. The diffraction patterns obtained from the experiments look similar to those expected for a superstructure. Nevertheless, they can be interpreted as crystallographically oriented precipitations of YB₂C₂ and Ni₂B within the YNi₂B₂C crystal, formed during the cooling process. The orientation relation between the lattices was obtained from experimental neutron and X-ray data. Structure refinements of the collected X-ray data were performed by separation of the intensity data of the individual phases. Scanning electron microscopy images of the inclusions found on a polished cross section of the crystal are presented; their chemical composition was determined using wavelength-dispersive X-ray analysis.

Abstract. Thin SrTiO₃/La_0.7Sr_0.3MnO₃ (STO/LSMO) films of 30 nm thickness were epitaxially grown on a (001) Pb(Mg_1/3Nb_2/3)O₃-28 mol % PbTiO₃ piezoelectric single-crystalline plate and investigated by means of wide-angle X-ray scattering in situ under the influence of a direct current electric field with strength E up to ±18 kV/cm. The strain s in the films could by tuned dynamically due to a dominant converse piezoelectric effect of the substrate. The coefficient of coupling between electric field-induced strain alteration of the substrate and the buffer film (LSMO) is approximately 0.75, whereas for the substrate and top films (STO) it is about 0.35 related to a normalized strain alteration of the substrate of 1.

Abstract. Mechanical properties of LiB₃O₅ single crystal plates with different orientation as well as of glass with the same composition have been investigated. The nano- (H) and microhardness (H_M), the reduced Young’s modulus (E_r) and the crack behaviour of the samples were studied. Both hardness and Young’s modulus of glass appeared smaller in comparison to corresponding single crystal data (H ~ 7 - 8 GPa, H_M ~ 6 GPa, E_r ~ 70 - 80 GPa for glass and H ~ 10 - 15 GPa, H_M ~ 6 - 11 GPa, E_r ~ 93 - 155 GPa for single crystal). H, E_r, and the plane of crack propagation proved orientation-dependent. Cracks in the glass sample were not observed up to 0.49 N microindentation load, whereas for the single crystal the cracks appeared already at 0.098 N. In single crystals the observed cleavage planes {211} and/or {412} are oriented nearly parallel to planes of B-O rings.

Abstract. Nanohardness (H) and microhardness (H_M) of sodium borosilicate glasses with and without nanopores have been studied. From nanoindentation measurements along with hardness H also Young's modulus E has been derived. While both H and H_M varied between ~10 GPa and ~7 GPa for the bulk glass, values for nanoporous specimens were an order of magnitude lower at about 0.5 GPa. Young's moduli were found ~82 GPa and ~5 GPa for bulk and porous glass, respectively. Cracks and pile-ups have been observed, respectively, arising from microindents and nanoindents in bulk glass whereas none of them could be detected in nanoporous material. Molecular structure of both glasses studied by X-ray diffraction is similar.

Abstract. The capabilities of an Si(511) channel-cut monochromator used with an X-ray tube with copper anode are presented. By passing this Si(511) channel-cut crystal, X-rays get both monochromatic and linearly polarized. The monochromaticity of the resulting beam is proved by angular dispersive measurements. Elastic scattering was used to characterize the degree of linear polarization.

Abstract. Oriented thin films of perovskite-related Sr_n+1Ti_nO_3n+1 Ruddlesden-Popper phases (n = 1, 2, 3) were grown on (001) single-crystalline SrTiO₃ substrates. Preparation of the films was carried out by wet chemical deposition from metalorganic Sr-Ti solutions (rich in Sr) and subsequent conversion into the crystalline state by thermal treatment in air atmosphere at a maximum temperature of 700 °C. Solutions were prepared by a modified Pechini method. The films were investigated by wide-angle X-ray scattering and high-resolution transmission electron microscopy. The phase content of powders prepared from the dried solutions and annealed under similar conditions differed from that present in the films, i.e. only polycrystalline SrTiO₃ was detected together with oxides of Ti and Sr.

Abstract. Single crystal X-ray diffraction (XRD), high-resolution electron holography and density functional calculations (DFT) are employed to investigate single-crystalline BaTiO₃ in the noncentrosymmetric tetragonal phase. From XRD and DFT the structure parameters, the electron density and corresponding properties, such as atomic charges and the dipole moment are determined. For this purpose the maximum-entropy method was utilized to get accurate electron densities in the case of XRD, whereas all-electron calculations were performed in the framework of DFT. A comparison of experimental results and density functional calculations yield a rather good agreement. The electron density distributions are used to determine the “natural” unit cell corresponding to the neutral boundary cells of the whole crystal and its dipole moment, providing the boundary conditions necessary for calculating the electrostatic potential within the unit cell through the Poisson equation. The electrostatic potential was then utilized to perform electron scattering simulations within the framework of the Multislice formalism, resembling unique features of experimentally recorded electron holograms. It is shown that the phase wedge in the scattered wave, which is due to the polarization field within the specimen, is essential for the image reconstruction. This essential feature has not been included in simulations before.

Caption. The upper right shows a scheme of the unit-cell of tetragonal BaTiO₃ [a = 3.9946(2) Å, c = 4.0388(5) Å], noncentrosymmetric space-group (99) P4mm, with tetragonal distortion pointing along c direction.
On the lower right ED difference maps ρ_dif = ρ_LDA-ρ_XRD of (010)-crystal plane at b = 0 Å (i. e., y = 0) (a) and b = 1.997 Å (y = 0.5) (b) are shown. The black contour lines characterizing constant positive differences are drawn at ρ =2ⁿ e/ų n ∈ {-2, -1, ..., 4}. The gray lines characterizing negative differences at the same values.

Abstract. The steel of Damascus blades, which were first encountered by the Crusaders when fighting against Muslims, had features not found in European steels - a characteristic wavy banding pattern known as damask, extraordinary mechanical properties, and an exceptionally sharp cutting edge. Here we use high-resolution transmission electron microscopy to examine a sample of Damascus sabre steel from the seventeenth century and find that it contains carbon nanotubes as well as cementite nanowires. This microstructure may offer insight into the beautiful banding pattern of the ultrahigh-carbon steel created from an ancient recipe that was lost long ago.

Caption. High-resolution transmission electron microscopy image of carbon nanotubes in a genuine Damascus sabre after dissolution in hydrochloric acid is shown at the upper right. Multiwalled tubes with the characteristic layer distance d = 0.34 nm, as indicated by the Fourier transforms (see inset). Scale bar: 5 nm. Below an ancient damascene blade is shown (picture by A. Dietsch).

Abstract. Reversible structural changes of near-electrode regions of an (001) SrTiO₃ (STO) single-crystal plate with perovskite-type of structure in an external electric field are described as the tunable and reversible formation of significant volume of domains containing Ruddlesden-Popper (RP) phases of composition SrO(SrTiO₃)_n with variable n. Compositional changes are discussed to be caused by electromigration of ion complexes in the static electric field, i.e. by solid state electrolysis of the perovskite STO. Electromigration is initiated by the electric field which then stabilizes the RP domains formed. The RP domains can be described as coherently intergrown with the surrounding perovskite matrix. The X-ray scattering behaviour of these intergrowths, compared with the perovskite STO, suggests the technical use of the phenomenon for adaptive X-ray optics.

Abstract. An (001) single-crystal plate PbMg_1/3Nb_2/3O₃-28 mol % PbTiO₃ was investigated by wide-angle X-ray scattering at room temperature in situ under the influence of an external static electric field E applied along the [001] direction of the specimen. Excluding an initial stage of the electric field processing, the induced strain s calculated from the change of interplanar spacing exhibited a symmetrical increase with |E| and an anhysteretic character of the s(E) dependence during unidirectional loops of the applied electric field. Causes of the observed s(E) behaviour are discussed.

Abstract. An incommensurately modulated structure of CeSi_1.82 as determined by single-crystal X-ray diffraction at room temperature is reported. The observed satellite reflections reduce the orthorhombic symmetry of the X-ray pattern to a monoclinic one. This suggests the description of the modulated structure in the monoclinic superspace group I2/b(αβ0)00. The modulation wave vector was determined to q = 0.410(1) ⋅ a* + 0.610(1) ⋅ b*. The refinement was done using harmonic modulation functions for the displacement and the occupation probability of the atoms, the quality parameters converged to R_obs = 3.33% (R_obs = 2.56% for the main reflections, R_obs = 8.88% for the 1st order satellite reflections and R_obs = 33.06% for the 2nd order satellite reflections). The origin of the observed satellite reflections is attributed to a modulation of the partly occupied Si site caused by composition changes within the crystal.