Electron paramagnetic resonance (EPR) investigations of BaTiO3  +  0.04 BaO  +  x/2 Fe2O3 (0.007  ⩽  x  ⩽  0.05) ceramics and BaTi0.98Fe0.02O3 single crystals were performed to study the incorporation of Fe ions in the hexagonal 6H-BaTiO3 lattice and their defect properties. The samples were characterized by x-ray diffraction and wavelength-dispersive x-ray electron probe microanalysis. EPR spectra were recorded both in X- and Q-bands at room temperature. Angle-dependent single crystal EPR investigations and simulations of the ceramic powder EPR spectra revealed three different centers, which can be attributed to Fe3+ ions incorporated on crystallographically different Ti sites. Only one of them was already known before. Two spectra with axial symmetry belong to isolated Fe3+ ions incorporated at Ti(1) sites (exclusively corner-sharing oxygen octahedra) and Ti(2) sites (face-sharing octahedra). The difference of their spectral parameters arises from the different trigonal distortions of the two types of octahedra. The third spectrum has orthorhombic symmetry and is caused by Fe3+ centers associated with a nearest-neighbor charge-compensating oxygen vacancy. A model for the location of this associate is proposed.

We have investigated recrystallization of amorphous Yttrium Iron Garnet (YIG) by annealing in oxygen atmosphere. Our findings show that well below the melting temperature the material transforms into a fully epitaxial layer with exceptional quality, both structural and magnetic. In ferromagnetic resonance (FMR) ultra low damping and extremely narrow linewidth can be observed. For a 56 nm thick layer a damping constant of α=(6.63±1.50)·10^-5 is found and the linewidth at 9.6 GHz is as small as 1.30±0.05 Oe which are the lowest values for PLD grown thin films reported so far. Even for a 20 nm thick layer a damping constant of α=(7.51±1.40)·10^-5 is found which is the lowest value for ultrathin films published so far. The FMR linewidth in this case is 3.49±0.10 Oe at 9.6 GHz. Our results not only present a method of depositing thin film YIG of unprecedented quality but also open up new options for the fabrication of thin film complex oxides or even other crystalline materials.

We report on Sn-contained nanocrystals formed in Si and SiGe matrixes via Sn precipitation upon annealing of thin metastable Si1−x−yGexSny layers grown by molecular beam epitaxy. The nanocrystals exhibit a cubic lattice, which is coherent with the matrix. The density of the nanocrystals decreases with the annealing temperature revealing a kinetic formation pathway. New optical spectral features below the Si band gap are observed in photoluminescence spectra of the samples with nanocrystals. The origin of these new spectral features is discussed.

We report on novel defect-free SiSn/Si heterostructures grown pseudomorphically on Si(001) substrates using temperature-modulated molecular beam epitaxy. This approach results in a sustainable epitaxial growth for SiSn/Si multilayers. Transmission electron microscopy and electron diffraction manifest that SiSn layers possess a diamond lattice structure. X-ray diffraction reveals up to 9.5 at% Sn in the crystal lattice of SiSn layers.

Self-assembled nanostructures have attracted much interest in the last time because of promising properties for possible device applications. Beside CVD and MBE liquid phase epitaxy (LPE) established as an advantageous growth technique due to the vicinity to the thermodynamic equilibrium which affords very regular structures. Beside the ex-situ analysis [e.g. 1, 2] the in-situ investigations are essential to get a more precise understanding of the growth process.

We report on the in situ observation during liquid phase epitaxy (LPE) of Stranski-Krastanow grown SiGe/Si(001) islands with X-ray diffraction methods. Therefore, we developed a growth chamber combined with pre-processed samples which afford LPE under N-2 atmosphere (instead of H-2 which is normally used for LPE) at a synchrotron beamline. The island evolution is probed with X-ray diffraction methods from the backside of a thin silicon substrate which floats on the melt. The way towards LPE in situ X-ray diffraction experiments will be described. Our results show the development of X-ray diffraction signals in dependence of the current growth state. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

A series of glass ceramics was prepared and the structure–property relationships evaluated. The base composition of the series was comprised of fluorozirconate (FZ) and fluorochlorozirconate (FCZ) glass ceramics. Thermal processing of as-made FCZ-based glass ceramics produced sharp peaks in X-ray diffraction patterns, which was attributed to BaCl2 nanocrystals formed in the material; this was not observed in the FZ glass. Up-conversion fluorescence experiments were carried out for both the FZ and FCZ samples doped with erbium. The fact that an increase in the up-conversion efficiency was not observed indicates that erbium ions were not embedded in the BaCl2 nanocrystals. A comparison is made between this series and a similar series that was doped with neodymium.

Fluorozirconate-based glasses have been doped with samarium and bromine ions. Thermal processing initiates the formation of barium bromide nanocrystals in the glass. Samarium enters the glass matrix either in its divalent or in its trivalent state. Fluorescence measurements indicate that during the annealing process Sm2+ ions enter the nanocrystals leading to enhanced fluorescence efficiency and to changes in the fluorescence lifetime.

Optically active fluorozirconate-based (FZ) glass ceramics offer a broad range of applications. The functionality of the glass ceramic can be modified by appropriate doping and thermal processing performed after the glass production. For use in digital radiography, for example, the FZ glass has been doped with europium and chlorine ions [1, 2]. Thermal processing by annealing in the vicinity of the glass transition temperature produces barium chloride nano-crystals in the glass. The glass ceramic can act either as a scintillator (able to convert ionizing radiation to visible light) [1], or as a storage phosphor (able to convert the radiation into stable electron-hole pairs, which can be read out afterwards with a scanning laser beam in a so-called “photostimulated luminescence“ process) [2].

The elastic behavior of molecular beam epitaxy-grown SiGe/Si(111) nanowhiskers (NWs) has been studied by means of electron microscopy, x-ray scattering, and numerical linear elasticity theory. Highly brilliant synchrotron radiation was applied to map the diffusely scattered intensity near the asymmetric (115) reciprocal lattice point. The larger lattice parameter with respect to the Si matrix causes a lateral lattice expansion within embedded Ge layers. This enables a clear separation of scattering due to NWs and laterally confined areas aside. Finite element calculations prove a lateral lattice compression in the Si matrix close to the NW apex above buried threefold and single Ge layer stacks. This suggests an incorporation probability, which additionally depends on the radial position within heteroepitaxial NWs.

The forming and decomposition of Al84Ce6Ni10 and Al81Ce10Ni9 glasses produced by melt spinning under different melt temperatures and cooling rates was investigated by means of x-ray diffraction (XRD), electron microscopy (TEM and ESEM), electrical resistivity (ER) and calorimetric measurements during isothermal and continuous heating. The influence of the different production conditions on the relaxation, glass transition and crystallization are analysed. In the Al84Ce6Ni10 glasses the melt temperature and cooling rate do not have a strong influence on the glass forming, the transition to the supercooled liquid (SL) and the formation of a eutectic as the first crystalline structure. In the Al81Ce10Ni9 materials the different synthesis conditions produce fully or partial amorphous structure in the as-quenched state. The transformation to the crystalline structure without glass transition occurs with the formation of NC-fcc Al (nanocrystals) before a eutectic crystallization is dominant.

We report multi-layer ZnO nanosheets obtained by annealing Zn polyhedral particles in pure O-2. The structure comprises a cluster core with side faces terminated with 50-nm-thick multi-layer sheets. The nanosheets were found to be (0001)-oriented single-crystalline wurtzite ZnO. By studying the early growth stages, it appears that the sheets form through a ripening process of dendritic ZnO nanostructures, during which the single-crystalline nature and crystallographic orientation are conserved. The ripening is promoted by the rapid oxidation of the Zn polyhedral microcrystals. We also show that appropriate modification of the oxidation process leads to the formation of well-defined dendritic nanowires. The optical properties (photoluminescence and Raman) of these nanostructured materials are discussed.

Linear and nonlinear elastic effects occuring in a single crystal of the ternary alloy Ni40Ti50Cu10 were determined with a modified ultrasonic pulse echo-overlap technique at different temperatures. All linear elastic coefficients could be measured above and below the martensitic transformation supplementing the results of [A. Alippi (Ed.), Proceedings of the International Conference on Acoustics, Rome, 2001]. A large jump of the elastic stiffness c44 could be detected. First nonlinear elastic measurements were performed. No substantial increase of anharmonicity could be found. The maximum stress amplitude was held far below the yield stress of the material.

An introduction to polarisation phenomena observed at X-ray diffraction is given. Using an arrangement being analogous to optics of visible light, the polarisation state of the diffracted beam has been investigated using quarter wave plates. Depolarisation phenomena at the excitation of a noncoplanar many-beam geometry are shown for lithium fluoride samples. The results are explained in terms of incoherent diffraction, as known from light optics.

An Al25La50Ni25 and newly discovered Al38Dy50Ni12, Al38Dy50Co12 and Al41Dy47Ni6Co6 glasses prepared by melt-spinning were studied by means of electrical resistance (ER) and calorimetric measurements at constant and at linearly increasing temperatures as well as by X-ray diffraction (XRD) and microhardness studies after different heat treatments. Changes in short-range order during relaxation lead to prepeaks in XRD spectra, ER and hardness increases. The glass transitions are accompanied by endothermal heat effects and ER drops. In Al25La50Ni25, crystallisation sets in above 240 °C via the formation of metastable LaNi and AlLa3 phases which may transform into La(Ni, Al). The Al38Dy50Ni12 glass crystallises only above 400 °C; fine precipitates of Dy3Ni and probably DyAl appear before a Dy(Ni, Al) phase forms. The Co-containing materials possess still increased stability but are very brittle.

The decomposition of Al84Dy6Ni10 and Al84Dy8Ni6Co2 glasses prepared by melt spinning was investigated by means of X-ray diffraction (XRD), electrical resistivity (ER), calorimetric and microhardness measurements during isothermal, isochronal and continuous heating. Irreversible and reversible relaxation phenomena as well as glass transition occur before a primary crystallisation reaction in the ternary and a eutectic-type reaction in the quaternary alloy followed by the precipitation and transformation of intermetallic phases. Short- (SRO) and medium-range order (MRO) changes are responsible for pre-peaks in the structure factor observable even at room temperature. Glass transition (GT) is accompanied by resistivity drops. The first crystallisation products have a very fine morphology which raises the hardness of the alloys.

Series of experimental pinhole topographs are presented, which were taken by exciting a perfect, plane-parallel crystal plate in the three-beam case of diffraction. These images depict the energy flow inside the crystal. Therefore, modifications of the energy flow in the three-beam cases can be made visible directly. In this paper we investigate the effects of changing the coupling strength or the triplet phase between the two primary reflections. The experimental results are compared with simulations of the recorded intensity distributions and discussed with reference to the course of the dispersion surface.

Partially or fully amorphous Al89Dy11, Al84Dy11Co5 and Al84Dy6Co10 alloys were prepared by melt spinning. The amorphous to crystalline and subsequent transitions were studied with X-ray diffraction, electrical resistivity, thermal and microhardness measurements. The transformation kinetics were analysed in terms of the classical and the generalized Johnson–Mehl–Avrami–Kolmogorov models for nucleation and growth processes. In amorphous Al89Dy11, crystallization begins with α(fcc Al) formation closely followed by γ(Al3Dy), which transforms to α(Al3Dy). Addition of Co increases the stability of the amorphous states. The first crystallization process in the ternary alloys is eutectic-like; nanocrystals are present in Al84Dy6Co10. Annealing in the region of structural relaxation retards subsequent crystallization.

A new kind of topographic experiment is presented which makes it possible to depict the energy how in the three-beam case of diffraction in Laue-Laue geometry. The crystal is illuminated by a highly collimated x-ray beam which is reduced in both cross-section dimensions (pinhole topography).These experiments allow the investigation of the dynamical interaction of the three diffracted waves in three-beam interference and also allow the predictions of the theory to be rested. The results are discussed with reference to the dispersion surface and are compared with the images taken in the arrangement for conventional slit limited section topography.

Section topographs taken in three-beam diffraction geometry and in the neighbourhood of this geometric position are presented. The experiments were performed using polychromatic and monochromatic X-ray radiation. The interference of the two diffracted waves produces new contrast phenomena compared to the two-beam case. The contrast changes are discussed on the basis of the Bethe approximation by means of the effective structure factor and with regard to the dispersion surface of the three-beam case.