Instrumental profile of MYTHEN detector in Debye-Scherrer geometry

The main aberrations affecting data collected with 1D position sensitive detectors in Debye-Scherrer capillary geometry are examined, and analytical corrections proposed. The equations are implemented in two of the most advanced software based on the Rietveld and Whole Powder Pattern Modelling methods, respectively, for structure and microstructure analysis. Application to MYTHEN, a fast single photon counting detector developed at the Swiss Light Source, is discussed in detai

Correlation between transport properties and lattice effects in the NdCoO3 based catalysts and sensor materials

This study presents correlations between the structural and transport properties of pure and doped neodymium cobaltate, a compound of great interest for its foreseen applications as catalyst, sensor and thermoelectric material. Neutron and x-ray powder diffraction data have been combined to carefully determine lattice constants and atomic positions and four probe direct current conductivity and thermoelectric power measurements allowed us to follow the thermal evolution of the transport properties of these compounds. The dramatic improvement of the room temperature conductivity of Nd0.8Ca0.2CoO3 with respect to the pure and the Na-doped compound is explained in terms of a different spin-state for the Co ions within this structure. The higher conductivity and the absence of anomalies in the thermal expansion makes the Ca-doped compound more attractive than the pure NdCoO3 in view of possible applications. The experimental data and the Co environment analysis here discussed, in particular bond lengths distortion and bending angles, are fully consistent with a spin state (low to intermediate) transition in NdCoO3Comment: 32 pages, 9 figure

New developments in structure analysis of powders using preferred orientation

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Colloidal semiconductor/magnetic heterostructures based on iron-oxide-functionalized brookite TiO2 nanorods

A flexible colloidal seeded-growth strategy has been developed to synthesize all-oxide semiconductor/magnetic hybrid nanocrystals (HNCs) in various topological arrangements, for which the dimensions of the constituent material domains can be controlled independently over a wide range. Our approach relies on driving preferential heterogeneous nucleation and growth of spinel cubic iron oxide (IO) domains onto brookite TiO2 nanorods (b-TiO2) with tailored geometric parameters, by means of time-programmed delivery of organometallic precursors into a suitable TiO2-loaded surfactant environment. The b-TiO2 seeds exhibit size-dependent accessibility towards IO under diffusion-controlled growth regime, which allows attainment of HNCs individually made of a single b-TiO2 section functionalized with either one or multiple nearly spherical IO domains. In spite of the dissimilarity of the respective crystal-phases, the two materials share large interfacial junctions without significant lattice strain being induced across the heterostructures. The synthetic achievements have been supported by a systematic morphological, compositional and structural characterization of the as-prepared HNCs, offering a mechanistic insight into the specific role of the seeds in the control of heterostructure formation in liquid media. In addition, the impact of the formed b-TiO2/IO heterojunctions on the magnetic properties of IO has also been assessed

Architectural Control of Seeded-Grown Magnetic−Semicondutor Iron Oxide−TiO2 Nanorod Heterostructures: The Role of Seeds in Topology Selection

A colloidal nonaqueous approach to semiconductor−magnetic hybrid nanocrystals (HNCs) with selectable heterodimer topologies and tunable geometric parameters is demonstrated. Brookite TiO2 nanorods, distinguished by a curved shape-tapered profile with richly faceted terminations, are exploited as substrate seeds onto which a single spherical domain of inverse spinel iron oxide can be epitaxially grown at either one apex or any location along their longitudinal sidewalls in a hot surfactant environment. The topologically controlled arrangement of the component material lattices, the crystallographic relationships holding between them, and strain distribution across individual heterostructures have been studied by combining X-ray diffraction and absorption techniques with high-resolution transmission electron microscopy investigations. Supported by such structural knowledge, the synthetic achievements are interpreted within the frame of various mechanistic models offering complementary views of HNC formation..

Topologically controlled growth of magnetic-metal-functionalized semiconductor oxide nanorods.

Colloidal semiconductor-magnetic hybrid nanocrystals with topologically controlled composition are fabricated by heterogeneous nucleation of spherical e-Co domains onto anatase TiO2 nanorods. The latter can be selectively decorated at either their tips or at multiple locations along their longitudinal sidewalls, forming lattice-matched heterointerfaces regardless of the metal deposition sites. The possibility of switching between either heterostructure growth modes arises from the facet-dependent chemical reactivity of the oxide seeds, which is governed mainly by selective adhesion of the surfactants rather than by small differences in misfit-induced interfacial strain at the relevant junction points

Colloidal Synthesis and Characterization of Tetrapod-Shaped Magnetic Nanocrystals

Tetrapod-shaped maghemite nanocrystals are synthesized by manipulating the decomposition of iron pentacarbonyl in a ternary surfactant mixture under mild thermal conditions. Adjustment of the reaction parameters allows for the systematic tuning of both the width and the length of the tetrapod arms, which grow preferentially along the 〈111〉 easy axis direction. Such degree of control leads to modulation of the magnetic behavior of the nanocrystals, which evolves systematically as their surface magnetization phase and shape anisotropy are progressively increased