Changes in the crystallization sequence upon sulfur addition in the Zr52.5Cu17.9Ni14.6Al10Ti5 bulk metallic glass-forming liquid revealed by in situ high-energy x-ray diffraction

Bulk metallic glasses (BMGs) surpass the strength of steels and possess the elasticity and formability of polymers. The key to obtain these properties is to conserve the amorphous structure of a metallic melt and avoid crystallization during processing. In this work, a change in the crystallization sequence in the widely used BMG Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105) upon the addition of sulfur (Zr51.45Cu17.54Ni14.31Al9.8Ti4.9S2; Vit105 S2) is revealed by in situ high-energy x-ray diffraction, both upon heating from the glassy state and upon cooling from the liquid state during electrostatic levitation. This methodology proves to be a powerful tool to elucidate the complete crystallization behavior of complex BMG-forming liquids. The experiments show that the addition of sulfur changes the crystallization sequence and phases in a different manner upon cooling from the liquid state than upon heating from the glassy state. The thermal stability at low temperatures upon heating is increased, as the supercooled liquid region is extended from 60 to 77 K and the glass transition temperature increases from 671 to 692 K. However, the thermal stability is decreased upon cooling, causing a reduced glass-forming ability

Microscopic structure and dynamics of glass forming Zr2Co melts and the impact of different late transition metals on the melt properties

We studied the short-range order and the atomic dynamics of stable and undercooled binary Zr2Co alloy melts as well as their density and viscosity. The containerless processing technique of electrostatic levitation was used to achieve deep undercooling and to avoid contaminations. Static structure factors are determined by combining this technique with neutron and high energy X-ray diffraction. Co self-diffusion coefficients are measured by quasielastic neutron scattering. Our results reveal that the short-range order of the Zr2Co melts closely resembles that previously observed for Zr64Ni36. We consider this as the origin of the very similar melt dynamics of these two alloys at same temperatures. On the other hand, the difference in the structure and dynamics when compared with those of Zr2Cu and Zr2Pd shows clearly that not only the atomic sizes, but also electronic properties or chemical bonding have an important influence on the melt properties of Zr-based glass forming melts

In situ Oxidation study of Pd-Rh Nanoparticles on MgAl2O4MgAl_2O_4(001)

Alloy nanoparticles on oxide supports are widely used as heterogeneous catalysts in reactions involving oxygen. Here we discuss the oxidation behavior of Pd–Rh alloy nanoparticles on MgAl2O4(001) supports with a particle diameter from 6–11 nm. As an In situ tool, we employed high energy grazing incidence X-ray diffraction at a photon energy of 85 keV. We find that physical vapor deposited Pd–Rh nanoparticles grow epitaxially on MgAl2O4(001) with a truncated octahedral shape over the whole concentration range. During our systematic oxidation experiments performed at 670 K in the pressure range from 10^−3 to 0.1 mbar, we observe for Rh containing nanoparticles the formation of two different Rh oxide phases, namely RhO2 and a spinel-like Rh3O4 phase. PdO formation is only observed for pure Pd nanoparticles. This oxidation induced segregation behavior is also reflected in the oxidation induced enlargement of the average nanoparticle lattice parameter towards to value for pure Pd. Our results have ramifications for the phase separation behavior of alloy nanocatalysts under varying reducing and oxidizing environments

Correction: Surface induced smectic order in ionic liquids – an X-ray reflectivity study of [C22C1im]+[NTf2]−[C_{22}C_{1}im]^{+}[NTf_{2}]^{−}

Surface induced smectic order was found for the ionic liquid 1-methyl-3-docosylimidazolium bis(trifluoromethlysulfonyl)imide by X-ray reflectivity and grazing incidence scattering experiments. Near the free liquid surface, an ordered structure of alternating layers composed of polar and non-polar moieties is observed. This leads to an oscillatory interfacial profile perpendicular to the liquid surface with a periodicity of 3.7 nm. Small angle X-ray scattering and polarized light microscopy measurements suggest that the observed surface structure is related to fluctuations into a metastable liquid crystalline SmA2 phase that was found by supercooling the bulk liquid. The observed surface ordering persists up to 157 °C, i.e. more than 88 K above the bulk melting temperature of 68.1 °C. Close to the bulk melting point, we find a thickness of the ordered layer of L = 30 nm. The dependency of L(τ) = Λ ln(τ/τ1) vs. reduced temperature τ follows a logarithmic growth law. In agreement with theory, the pre-factor Λ is governed by the correlation length of the isotropic bulk phase

Local structure of explosively welded titanium-stainless steel bimetal

Bimetals targeted for industrial applications are usually designed to combine the properties of two dissimilar metals, e.g. high strength, high hardness and low cost of steels with chemically resistive titanium. In this work the structure of one particular, but for industries very interesting, bimetallic system – Cr/Ni stainless steel clad with titanium has been studied. The material was prepared by explosion welding, a method capable of joining a wide variety of similar or dissimilar materials. Our analysis is based on X-ray micro-diffraction experimentation utilizing hard monochromatic X-rays focused down to micrometer size. In this way the bimetal in bulk form was analyzed and microstructural differences between the joined materials and their interface were determined.Web of Science106662762

Structure and Stability of Gd-doped CeO2\mathrm{CeO_2} Thin Films on Yttria-Stabilized Zirconia

25 nm thick Gd-doped ceria thin films were grown on Yttria-Stabilized Zirconia (YSZ) substrates with (110) and (111) orientation by pulsed laser deposition to study both their crystalline structure and interfacial stability. The films were characterized by high-energy grazing incidence x-ray diffraction, x-ray reflectivity and x-ray photoelectron spectroscopy before and after annealing to 1400 K under ultra-high vacuum (UHV) conditions. The films were found to be epitaxial to the YSZ substrates, exhibiting good crystalline quality without defects like twinning, and low surface roughness. Upon reduction due to the annealing in ultrahigh vacuum (UHV), both samples showed an increase in lattice parameter while maintaining their original crystalline quality. The x-ray reflectivity measurements gave evidence for interdiffusion after annealing by the presence of an additional interfacial layer with reduced electron density. X-ray photoelectron spectroscopy revealed an increase in the concentration of Ce$^3+$ and also yttrium at the surface upon annealing, indicating a slight reduction of the surface as well as diffusion of yttrium to the surface