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High-resolution thermal-expansion and specific-heat measurements were performed on single crystalline BaFe2(As1-xPx)2 (0 < x < 0.33, x = 1). The observation of clear anomalies allows to establish the thermodynamic phase diagram which features a small coexistence region of SDW and superconductivity with a steep rise of Tc on the underdoped side. Samples that undergo the tetragonal-orthorhombic structural transition are detwinned in situ, and the response of the sample length to the magneto-structural and superconducting transitions is studied for all three crystallographic directions. It is shown that a reduction of the magnetic order by superconductivity is reflected in all lattice parameters. On the overdoped side, superconductivity affects the lattice parameters in much the same way as the SDW on the underdoped side, suggesting an intimate relation between the two types of order. Moreover, the uniaxial pressure derivatives of Tc are calculated using the Ehrenfest relation and are found to be large and anisotropic. A correspondence between substitution and uniaxial pressure is established, i.e., uniaxial pressure along the b-axis (c-axis) corresponds to a decrease (increase) of the P content. By studying the electronic contribution to the thermal expansion we find evidence for a maximum of the electronic density of states at optimal doping.

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Besides promising applications for electronic nanostructures or nonlinear optical devices nanocrystalline Au may be used as efficient catalysis material (e.g. chemisorption of CO or hydrocarbons). The catalytic reaction is often very sensitive to the structure and size of the metal crystallites and their crystallographic orientation Both conditions may be controlled by growing the nanocrystals in a single crystalline non-metallic matrix. Here, Au nanocrystals were generated inside rutile TiO2 by implantation of 260 keV Au ions. The growth in a matrix allows to stabilize the precipitates structurally. Furthermore, no impurities were introduced because of mass separation during the process. However, the host crystal is damaged by the ion impact processes. This damage may be reduced by in situ or post-implantation annealing. Various x-ray scattering techniques were used for the structural characterization of the material: specular reflection for surface and near-surface studies, diffraction for determination of strain and crystal size, pole figure measurements to reveal the orientation relationship. In the as-implanted state randomly oriented crystals with a size of 5 … 7 nm as well as crystals oriented in a fibre texture with axis parallel to the rutile surface normal have been obtained. Annealing at 1000 K let the nanocrystals grow to 15 nm; simultaneously the amount of epitaxially oriented Au crystals increases. The orientation relationship is controlled by the crystallographic axis of the rutile matrix surface so that the ensemble of the Au nanocrystals fits to the crystal symmetry of the matrix: - the surface normal is the two-fold rutile [100] direction: surface normal - Au < 2 1 1 > || TiO2 < 1 0 0 > in the surface - Au < 1 1 0 > || TiO2 < 0 0 1 > and Au < 1 1 1 > || TiO2 < 0 1 0 >. In order to fulfil the two-fold matrix symmetry there are two groups of Au crystallites rotated by 180° each to other around the surface normal. - the surface normal is the four-fold rutile [001] direction: surface normal - Au || TiO2 In order to fulfil the four-fold matrix symmetry there are two groups of Au crystallites rotated by 90° each to other around the surface normal. Each of them is split into two sub-groups rotated by +9.7° and –9.7° around the surface normal from the “ideal” orientation: Au + 9.7° and –9.7° || TiO2 and Au + 9.7° and –9.7° || TiO2 .

Au-ions were implanted into TiO2 single crystals with doses ranging from 2x1016Au+/cm2 to 6x1016Au+/cm2 at RT and 1000 K. At RT implanted samples were then thermally annealed at temperatures of 550 K to 1550 K. The Au-atoms precipitate to nanocrystals already during implantation at RT with an average particle size of 1.5 nm. HRTEM investigations revealed that the Au-nanocrystals, embedded in amorphous TiO2 regions, have a broad size and range distribution varying from large sizes in the near surface region to smaller sizes at larger depths. In the annealing process a reorientation of the Au-nanocrystals is observed, with the main effect of a decrease of the (111) peak and an increase of the (200)-peak in the XRD spectra. After annealing at 1000 K the particle size of the highly textured Au-implant was evaluated to ~ 6 nm; this means that during annealing the particles grow, leading to a partially coherent orientation in the disordered TiO2-matrix. Au implantation at RT performed through a metal mask with holes resulted in a narrow size distribution (2-6 nm) of the Au-nanocrystals in the near surface region.