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The temperature dependence of the spontaneous strain in has been studied using triple-axis diffractometers of high momentum-space resolution for synchrotron radiation with energies above 100 keV. In the temperature range from 40 to 80 K the experimental data are in excellent agreement with a Landau theory taking into account the quantum mechanical zero-point fluctuations. At temperatures below 40 K a difference between experiment and theory of about 4% occurs which is considered as an indication for a novel phase in the quantum paraelectric regime. The difference between the fitted theory and the experimental data is nearly the same for all of the samples investigated; the biggest difference is observed in the fit parameter describing the theoretical saturation value of the spontaneous strain at zero temperature. In absolute numbers the measured spontaneous strain is strongly sample dependent, i.e. flux-grown, float-zone-grown and Verneuil-grown crystals show differences in the spontaneous strain of about 30% at 10 K. On the other hand, only small variations are observed in samples which were subjected to different heat treatments, which determine the number of oxygen vacancies.

Metal clusters were generated and stabilized in pore free, mechanically stable poly(amide imide) (PAI) polymer membranes in high dispersion and high concentration of typically 15wt-%. These membranes have been successfully tested for catalytic applications. Pure Pd-loaded and bimetallic Pd/Ag, Pd/Cu, Pd/Co, Pd/Pb PAI films were investigated by means of x-ray absorption spectroscopy, small and wide angle x-ray scattering and transmission electron microscopy to characterize the structure of the metal clusters in the protective polymer. The measurements consistently show a homogeneous distribution of metallic nanoclusters of 10–30 A size within the membranes. Also, a smaller amount of larger aggregates up to 300 A is observed in most of the films. The precise cluster size distribution critically depends on the solvents used as well as on other preparation parameters such as the stirring time of the metal precursor/polymer solution. In case of Pd/Ag and Pd/Pb bimetallic films no clear evidence for the formation of bimetallic clusters in the membrane, i.e. alloying of both metal components, is found. In Pd/Cu and Pd/Co membranes, chlorine from CuCl2 and CoCl2 precursors reacts with Pd which may influence the Pd catalytic behavior. Reduction and oxidation of the metal nanoclusters is quantitatively studied by means of x-ray absorption spectroscopy. Membrane properties are discussed with respect to catalytic applications.

The temperature dependence of the sharp and the broad component of the critical scattering above the cubic-to-tetragonal phase transition of ${\mathrm{SrTiO}}_{3}$ has been studied by means of high-resolution triple-crystal diffractometry using 100--200 keV synchrotron radiation in five samples differing with respect to growth technique and oxygen vacancy concentrations. Emphasis is on changes in the critical behavior, the critical temperature, and the strain fields at the transition from bulk to surface. The sharp component was observed only in surface near regions of highly perfect crystals and is coupled to the occurrence of a long-range strain gradient that was identified by an exponential increase of mosaicity, lattice parameter fluctuations, and Bragg-peak intensity when approaching the surface from the bulk of the sample. Vanishing of the sharp component was observed at the polished/etched surface of a platelet cut off the large perfect crystal after release of strain due to free bending of the platelet. The values of the critical temperature observed in the bulk of the different samples vary between $98.7l~{T}_{c}l~105.8 \mathrm{K}.$ In the surface near regions of a highly perfect float-zone grown crystal a variation of ${T}_{c}$ of about 0.5 K has been found. Concerning the broad component the critical exponent describing the temperature dependence of the inverse correlation length ${\ensuremath{\kappa}}_{b}$ varies between $0.73l~{\ensuremath{\nu}}_{b}l~1.19,$ the exponent for the susceptibility between $1.49l~{\ensuremath{\chi}}_{b}l~2.9,$ however, the ratio of the two exponents is almost sample independent and equal to ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}=2.1$ with a variance of 0.2, in good agreement with the theoretical value of 1.97 obtained by LeGouillou and Zinn-Justin [Phys. Rev. B 21, 3976 (1980)]. The occurrence of the sharp component did not affect significantly the critical exponents for the underlying broad component of the critical scattering. The exponents for the sharp component observed in surface near layers of about 100 $\ensuremath{\mu}\mathrm{m}$ thickness at the highly perfect float zone and flux grown crystals varied between $0.58l~{\ensuremath{\nu}}_{s}l~1.30,$ the values for the ratio varied between $3.3l~{\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}l~4.6.$ The average value of ${\ensuremath{\chi}}_{s}/{\ensuremath{\nu}}_{s}$ is 3.9 with a variance of 0.5, and is about twice the ratio ${\ensuremath{\chi}}_{b}/{\ensuremath{\nu}}_{b}$ for the broad component as suggested by Harris et al. [Phys. Rev. B 52, 14 420 (1995)].

Noble metal clusters were generated and stabilized in poly(amide imide) (PAI) polymers in high dispersion and high concentration of typically 15 wt %. The loaded polymers were prepared as pore-free, mechanically stable membranes, which have been successfully tested for catalytic activity in membrane reactors. Pure Pd- and Ag-loaded as well as bimetallic Pd/Ag, Pd/Cu, Pd/Co, and Pd/Pb PAI films were investigated by means of X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) to characterize the structure and morphology of the metal clusters in the protective polymer. The measurements consistently show a homogeneous distribution of metallic nanoclusters of 1−3 nm size with a smaller amount of larger aggregates up to 30 nm in some of the films. The precise cluster size and distribution critically depend on the solvents used (N-methyl-2-pyrrolidone, tetrahydrofuran) as well as on other preparation parameters such as the stirring time of the metal precursor...

Metal clusters were stabilized in poly(amide imide) (PAI) polymers in high dispersion and large amounts of metal loading of typically 15 wt-%. The loaded polymers are prepared as pore-free, mechanically stable membrane films. Pure Pd-loaded and bimetallic Pd/Ag, Pd/Cu PAI films were investigated by means of X-ray absorption spectroscopy (XAFS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) to characterize the structure of the metal clusters in the protective polymer. The reduction of nitrous oxide by Pd/Ag-loaded membranes in the membrane mode is demonstrated. Cluster sizes are calculated from the measured XAFS coordination numbers by use of an onion model which describes the clusters as spherical metal cores with uniform oxide surface layers. All measurements consistently show a homogeneous distribution of metallic nanoclusters of size 1-6 nm with a smaller amount of larger aggregates in most of the films. Indications of metal alloying in bimetallic films are generally weak. The precise cluster size distribution critically depends on the solvents used as well as on other preparation parameters. In Pd/Cu-loaded membranes which are judged to be amorphous from the XRD spectra. XAFS clearly demonstrates a reaction of Pd with chlorine from CuCl 2 precursors which may influence the Pd catalytic behavior. Reduction behavior of the metal nanoclusters at 300K is linked by means of the onion model to microscopic quantities.