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The atomic structure and phase separation of amorphous Si-B-C-N ceramic powder samples obtained by thermolysis of boron-modified polysilazanes were investigated using X-ray and neutron diffraction in the wide-angle and small-angle scattering regimes. The short-range order of the Si-B-C-N ceramics corresponds to that of Si-C-N ceramics consisting of two separated amorphous phases: an amorphous graphite-like phase and amorphous Si 3+(1/4)x N 4-x C x (x ) 0-4). The evaluation of the total pair correlation functions revealed that the boron atoms are bonded to nitrogen with B-N bond lengths typical for h-BN. These units are incorporated in the graphite-like phase not statistically, but within regions of BN-rings which are less extended than the regions formed by C-rings. X-ray diffraction phase analysis and small-angle scattering showed that the addition of up to 10 at. % of boron to Si-C-N ceramics significantly influences the high-temperature behavior of the ceramics: coarsening of the separated amorphous phases, the crystallization of Si 3 N 4 and its decomposition are retarded, and evolution of a nanocrystalline SiC phase is observed.

Ferromagnetic, pure ZnO films were grown on Al2O3 substrates at various nitrogen pressures (0.01–1.0 mbar) and investigated with x-ray diffraction (XRD) and x-ray absorption spectroscopy. According to XRD data, the crystalline films were composed of crystallites of approximately 50 nm in size, oriented with respect to the substrates, and the lattice spacings show slight deviations with respect to single-crystalline ZnO of wurtzite structure. The parameters determined by XRD agree with those determined by extended x-ray absorption fine structure, except for the sample grown at the lowest N2 pressure of 0.01 mbar, which was attributed to deviations from the ZnO single crystals. The results for the ZnO films grown at 0.1 to 1.0 mbar partial N2 pressure indicate wurtzite unit cells compressed along the c axis. The x-ray absorption near-edge structure (XANES) spectra exhibited a strong dependence on the x-ray polarization and on nitrogen partial pressure, which was explained by the increase in the concentration of defects with nitrogen partial pressure and by interface or grain boundary effects. First-principles calculations using multiple-scattering formalism suggested that the XANES spectra changes were because of increasing Zn vacancy concentration with increasing nitrogen pressure. The results indicated that Zn vacancy defects play a significant role in the ferromagnetism of these films.

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We report small angle neutron scattering of spontaneous and magnetic field aligned components of the helical spin polarization in MnSi for temperatures T down to 0.35 K, at pressures p up to 21 kbar, and magnetic field B up to 0.7 T. The parameter range of our study spans the first order transition between helical order and partial magnetic order at p{c}=14.6 kbar, which coincides with the onset of an extended regime of non-Fermi liquid resistivity. Our study suggests that MnSi above p{c} is not dominated by the remnants of the first order transition at p{c}, but that an unidentified mechanism favors stabilization of a new ground state other than helical order.

Amorphous Si-C-N ceramics were produced over a wide range of compositions by thermolysis of structurally different polysilazanes. The structure of the as-thermolyzed amorphous ceramics and of ceramic samples after additional heat treatments was investigated by diffraction experiments in the wide-angle and the small-angle scattering regimes. Adopting contrast variation by combination of X-rays and neutrons and isotopic substitution, the observed correlations were assigned to individual atomic pairs. The atomic distances found in the ceramics correspond well with the distances in graphite and R-Si 3 N 4 . Using the concentration contrast method it could be shown quantitatively that the amorphous Si-C-N ceramics consist of an amorphous graphite-like phase and of amorphous Si 3+(1/4)x N 4-x C x (x ) 0-4). The partial pair correlation functions of the two phases could be evaluated. The size of the phase-separated regions, of the order of 10 Å in the as-thermolyzed ceramics, as determined from small-angle scattering, increases upon annealing up to some 10 Å. The partial structure factor of the amorphous carbon phase was simulated by a model. The simulation shows that the atomic arrangement of the amorphous carbon phase in Si-C-N ceramics in the layers is similar to that of glassy carbon, but the order between the layers is less pronounced. With increasing temperature the arrangement of the layers approaches the order in glassy carbon. A sputter-deposited Si-C-N ceramic shows similar short-range order, but no phase separation on a medium-range scale, as compared with precursor-derived ceramics.

A comparison between the resonant scattering curve obtained by anomalous small-angle X-ray scattering at the X-ray absorption edge of Ni and the complementary small-angle neutron scattering curve from an Al 89 Ni 6 La 5 alloy sample is reported. The sample does not comply with the two-phase approximation. The two resulting scattering curves are approximately proportional to each other in this particular case. The anomalous small-angle X-ray scattering resonant curve at the Ni absorption edge equals the Ni-Ni partial structure factor and, owing to the favourable neutron scattering lengths of Ni, La and Al, the neutron scattering curve is also proportional to that partial structure factor.