26 research outputs found
X-Ray Diffuse Scattering Study on Ionic-Pair Displacement Correlations in Relaxor Lead Magnesium Niobate
Ionic-pair equal-time displacement correlations in relaxor lead magnesium
niobate, , have been investigated at room
temperature in terms of an x-ray diffuse scattering technique. Functions of the
distinct correlations have been determined quantitatively. The results show the
significantly strong rhombohedral-polar correlations regarding Pb-O, Mg/Nb-O,
and O-O' pairs. Their spatial distribution forms an ellipse or a sphere with
the radii of 30-80. This observation of local structure in the system
proves precursory presence of the polar microregions in the paraelectric state
which leads to the dielectric dispersion.Comment: 11 pages, 3 figure
Gas-induced segregation in Pt-Rh alloy nanoparticles observed by in-situ Bragg coherent diffraction imaging
Bimetallic catalysts can undergo segregation or redistribution of the metals
driven by oxidizing and reducing environments. Bragg coherent diffraction
imaging (BCDI) was used to relate displacement fields to compositional
distributions in crystalline Pt-Rh alloy nanoparticles. 3D images of internal
composition showed that the radial distribution of compositions reverses
partially between the surface shell and the core when gas flow changes between
O2 and H2. Our observation suggests that the elemental segregation of
nanoparticle catalysts should be highly active during heterogeneous catalysis
and can be a controlling factor in synthesis of electrocatalysts. In addition,
our study exemplifies applications of BCDI for in situ 3D imaging of internal
equilibrium compositions in other bimetallic alloy nanoparticles
The effect of interlayer interactions on the ferroelectric–paraelectric phase transition in multilayered thin films of vinylidene fluoride– trifluoroethylene copolymers
The interaction between ferroelectric polymer films with different transition temperatures is evident in the effect of layer thickness on the ferroelectric– paraelectric phase transition in multilayer films, as revealed by x-ray diffraction and dielectric measurements. The multilayer samples consisted of alternating Langmuir–Blodgett (LB) films of two different copolymers of vinylidene fluoride with trifluoroethylene, one with 80% vinylidene fluoride and a ferroelectric– paraelectric transition temperature on heating of 133 ± 4 °C and the other with 50% vinylidene fluoride and a transition temperature of 70 ± 4 °C. Samples with a repeat period of 20 LB layers (10 contiguous layers of each composition) exhibited two distinct phase transitions, indicative of minimal interaction between the two materials. Films with a repeat period of 2, or films made from an equal mixture of the two copolymers, exhibited composite behavior, with an intermediate transition temperature and suppression of the transitions associated with the individual compositions. Films with a repeat period of 10 exhibit cross-over behavior. These results imply that the ferroelectric interaction length along the (110) direction, which is perpendicular to the film plane, is approximately 11 nm
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Early stages in the high temperature cyclic oxidation of {beta}-NiAl: An x-ray reflectivity study
Early stages in the cyclic oxidation of {beta}-NiAl at 500{degrees}C, 600{degrees}C, 700{degrees}C and 800{degrees}C were investigated using the technique of x-ray reflectivity. By fitting the data to a model function, oxide layer thickness, roughness of the oxide-vapor interface, and the roughness of the oxide-substrate interface were obtained as a function of oxidation time and temperature of oxidation. The time dependence of the oxide thickness was observed to be logarithmic at lower temperatures (500{degrees}C and 600{degrees}C) while a conventional t{sup 0.5} kinetics was observed at the higher temperatures. Comparison of the roughness of the oxide-substrate interface with that of the oxide-vapor interface shows that for comparable oxide thicknesses and identical substrate conditions, the oxide-vapor interface was rougher than the oxide-substrate interface at all temperatures. This is consistent with the previously postulated growth mechanism (outward diffusion of cations) for oxide growth during the early stages of oxidation at these temperatures. Thus, x-ray reflectivity offers a convenient way of determining the oxide growth rates, and the roughness of the interfaces when the oxide layer is thin; this regime cannot be easily studied with the techniques that are currently used for oxidation studies
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In situ x-ray scattering study of incipient formation of porous silicon
The incipient formation of porous silicon at the solution/silicon interface was examined in situ using synchrotron x-ray scattering techniques. The measurements were performed in a transmission x-ray/electrochemistry cell with p{sup +} type silicon single crystals. The structure of pores near the interface is determined from x-ray reflectivity and diffuse-scattering measurements. We found an interfacial layer with tapered cylindrical pores, followed by a layer of uniform porosity with increased branching with depth. For our conditions, the porosity was around 50%, and the pore diameter was about 50 to 70 {Angstrom}