A method is presented for indexing the powder diffraction lines from incommensurate structures by a systematic search of reciprocal space, choosing a propagation vector length derived from a satellite reflection in the powder diagram. An interactive computer program gives a graphical display of the direction of the propagation vector which gives the best fit to the pattern.
We investigated the short-range order of D interstitials in cubic ( alpha '-phase) VD0.75 by neutron diffraction (room temperature measurements, powder sample). The VDx system is particularly favourable for neutron scattering experiments studying the short-range order of hydrogen interstitials in metals since the coherent scattering cross section of D exceeds the coherent cross section of V by a factor of approximately=300. This allows a data analysis that assumes that only the D atoms contribute to the coherent scattering intensity. The measured diffuse scattering intensity shows a nearly complete blocking of interstitial sites in the two nearest shells around a given D atom, and a reduced occupation probability for the sites in the third shell. The results indicate the existence of a strong short-range and repulsive interaction between the D atoms.
The additional screening charge around 3d-transition metal impurities in A1 which is localized inside the muffin-tin sphere around the impurity is calculated. From the results it is concluded that the greatest part of the charge perturbation due to the impurity is screened within a spherical region of radius TIIT. This result is in agreement with the assumption of strongly localized impurities usually applied in the theory of substitutional impurities in metals.Umladungseffekte, verbunden mit dem Einbau von 3d-Ubergangsmetallpunktdefekten in Al, werden diskutiert. Die Resultate zeigen, daB der groBte Teil der Ladungsstorung innerhalb einer Kugcl mit dem muffin-tin-Radius um den Punktdefekt abgeschirrnt wird. Dieses Resultat unterstiit,zt das Modell stark lokalisierter Punktdefekte, das ublicherweise zur Beschreibung der Eigenschaften von substitutionellen Punktdefekten in Metallen angewandt wird.
The charge density oscillations around 3d transition metal impurities in aluminium are discussed. Comparing the asymptotic and pre-asymptotic results, in the pre-asymptotic case a reduction of the amplitude of the charge density oscillations is found. This reduction reflects the energy dependence of the impurity scattering phase shifts.Es werden die Ladungsdichteoszillationen in der Umgebung von 3d-~bergangsmetallpunktdefekten in Aluminium diskutiert. Dabei werden asymptotische und nichtasymptotische Resultate fur die Ladungsdichteoszillationen miteinander verglichen. Die nichtasymptotischen Oszillationen zeigen eine Verringerung der Amplitude, verglichen mit den asymptotischeri Oszillationen. Diese Amplitudenverringerung ist eine Folge der Energieabhgngigkeit der Streuphasen der Punktdefekte.
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