The effect of alloying Pd on the local lattice distortion (LLD) in the Ni and FeCoNiCr host matrixes is quantified by integrating local structure characterization and theoretical calculations. The local structure measurements reveal that the mean LLD in the FeCoNiCrPd high-entropy alloy (HEA) is twice as high as the Ni80Pd20 binary alloy though the FeCoNiCr base alloy has a negligible mean LLD. Density functional theory calculations unveil that the unexpected high mean LLD in FeCoNiCrPd is related to the high fluctuation of LLD in the FeCoNiCr matrix. These observations suggest a synergetic effect of chemical complexity on HEAs' mean LLD.

In order to study chemical complexity-induced lattice distortion in high-entropy alloys, the static Debye–Waller (D-W) factor of NiCoFeMnCr solid solution alloy is measured with low temperature neutron diffraction, ambient X-ray diffraction, and total scattering methods. The static atomic displacement parameter of the multi-element component alloy at 0 K is 0.035–0.041 Å, which is obvious larger than that of element Ni (∼ 0 Å). The atomic pair distance between individual atoms in the alloy investigated with extended X-ray absorption fine structure (EXAFS) measurements indicates that Mn has a slightly larger bond distance (∼0.4%) with neighbor atoms than that of others.

Severe lattice distortion is presumptively considered as a core effect of high-entropy alloys, but quantitative measurements are still missing. Here, we demonstrate that the lattice distortion in high-entropy alloys can be quantitatively analyzed based on pair distribution function obtained from synchrotron X-ray diffraction. By applying this method to equiatomic NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys, we found that the local lattice distortion in the NiCoCr (0.23%) and FeCoNiCrMn (0.24%) alloys are comparablewhile negligible in the FeCoNiCr alloy (0.04%). The origin of local lattice distortion in the NiCoCr and FeCoNiCrMn concentrated alloys was discussed. Published by Elsevier Ltd.

A major challenge for future nuclear reactors is to design nuclear materials that can sustain extremely prolonged radiation damage. Local lattice distortion, considered as a core effect of high-entropy alloys (HEAs), can suppress the growth of radiation defects to control radiation performance. However, local lattice distortion in HEAs is rarely quantitatively measured. Here we employed total scattering technique to study the local structure of the face-centered cubic (fcc) equiatomic FeCoNiCr MEA, and FeCoNiCrMn and FeCoNiCrPd HEAs before and after ion irradiation. Their local lattice distortions were quantitatively evaluated based on the difference of lattice constant between the local structure and the average structure. We revealed that the mean local lattice distortion in the pristine samples varies in the following order: FeCoNiCr < FeCoNiCrMn < FeCoNiCrPd. Density functional theory (DFT) calculations further unveiled that the fluctuation of local distortions in FeCoNiCr and FeCoNiCrMn is less than 5%, whereas the highest bond-length fluctuation in FeCoNiCrPd can approach to 8%. Under irradiation the mean local lattice distortion in FeCoNiCr and FeCoNiCrMn evolves differently from FeCoNiCrPd by showing a relaxation behavior at low dose. And the impact of local lattice distortion on dislocation loops after a prolonged ion-irradiation was investigated by transmission electron microscope (TEM) and the underlying mechanism was discussed.

Multielement solid solution alloys are intrinsically disordered on the atomic scale, and many of their advanced properties originate from the local structural characteristics. The local structure of a NiCoCr solid solution alloy is measured with x-ray or neutron total scattering and extended x-ray absorption fine structure (EXAFS) techniques. The atomic pair distribution function analysis does not exhibit an observable structural distortion. However, an EXAFS analysis suggests that the Cr atoms are favorably bonded with Ni and Co in the solid solution alloys. This short-range order (SRO) may make an important contribution to the low values of the electrical and thermal conductivities of the Cr-alloyed solid solutions. In addition, an EXAFS analysis of Ni ion irradiated samples reveals that the degree of SRO in NiCoCr alloys is enhanced after irradiation.

Finite element simulations are carried out to follow the evolution of residual stresses in Ti-7Al (alpha-hcp) alloy, as developed under an applied stress gradient. A model built upon phenomenological mesoscopic field dislocation mechanics is employed to simulate the deformation behavior. Model predictions are validated with results generated from high energy X-ray diffraction experiments using synchrotron radiation. These experiments provide for important simulation input, viz. grain positions and orientations, and strain rate sensitivities of the prismatic and basal slip systems of Ti-7Al. X-ray diffraction data obtained from individual grains enabled calculation of strain rate sensitivities of the prismatic and basal slip systems and the values are estimated as similar to 0.04 and similar to 0.02 respectively. Residual stresses at the length scale of individual grains and subgrains are successfully predicted and validated against experimental data. A key achievement of the present work is the measurement and simulation of residual stress gradients within individual grains. Conclusions from this work are that grains deform mainly via prismatic slip, and accurate characterization of rate-sensitivity is needed to model the development of grain-level residual stresses. (C) 2017 Elsevier Ltd. All rights reserved.

The atomic-level tunability that results from alloying multiple transition metals with d electrons in concentrated solid solution alloys (CSAs), including high-entropy alloys (HEAs), has produced remarkable properties for advanced energy applications, in particular, damage resistance in high-radiation environments. The key to understanding CSAs radiation performance is quantitatively characterizing their complex local physical and chemical environments. In this study, the local structure of a FeCoNiCrPd HEA is quantitatively analyzed with X-ray total scattering and extended X-ray absorption fine structure methods. Compared to FeCoNiCr and FeCoNiCrMn, FeCoNiCrPd with a quasi-random alloy structure has a strong local lattice distortion, which effectively pins radiation-induced defects. Distinct from a relaxation behavior in FeCoNiCr and FeCoNiCrMn, ion irradiation further enhanced the local lattice distortion in FeCoNiCrPd due to a preference for forming Pd-Pd atomic pairs.

X-ray absorption near-edge structures (XANES) at Si and C K-edge as well as X-ray excited optical luminescence (XEOL) have been used to investigate the electronic structures and optical properties of SiC microcrystals (SiCmcs) and SiC nanowires (SiCnws). SiCnws synthesized via thermal evaporation, have a SiC (β-phase)-core-SiO2-shell morphology. We found that the XANES for SiCmcs, a 6H-SiC (α-phase) structure, shows reasonable agreement with density functional theory (DFT) calculations. As for SiCnws, we observed both SiO2 and SiC features at the Si K-edge. It is interesting to note that upon X-ray excitation, SiCmcs emit bright light at the wavelength of 600 nm (2.07 eV), although bulk α-SiC has an indirect band-gap of 3.02 eV. SiCnws, on the other hand, exhibit luminescence at 460 nm with a shoulder at 600 nm. The analysis of these data and its implications are presented.

The electronic structure and optical properties of biaxial ZnO-ZnS heterostructure nanoribbons (NRs) have been investigated using x-ray absorption near-edge structures (XANES) and x-ray excited optical luminescence (XEOL). The XANES were recorded in total electron yield and wavelength-selected photoluminescence yield across the K- and L(3,2)-edges of zinc and sulfur and the K-edge of oxygen. The XEOL from the NRs exhibit a very weak band-gap emission at 392 nm and two intense defect emissions at 491 and 531 nm. The synchrotron x-ray pulse ( approximately 100 ps, 153 ns repetition rate) was used to track the optical decay dynamics from ZnO-ZnS NR, which can be described by two lifetimes (7.6 and 55 ns). Comparison with similar measurements for ZnO and ZnS nanowires reveals that the luminescence from ZnO-ZnS NRs was dominated by the ZnO component of the NR as the ZnS component contributes little. The implication of this observation is discussed.

We have studied X-ray absorption fine structures (XAFS) of Pt nanoparticles (PtNPs) which were deposited on silicon nanowires (SiNWs). SiNWs were fabricated via an electroless chemical etching method and served as the template for the immobilization of PtNPs. PtNPs electrolessly reduced from their ionic solution by HF-treated SiNWs were found to deposit on the tips of the SiNWs. The electronic structures of Pt were studied using X-ray absorption near-edge structures (XANES) at Pt L3,2-edge. For comparison, we also examined the Pt L3,2-edge and the Au L3-edge XANES of Pt-Au bimetallic nanoparticles co-deposited on SiNWs. We found that the PtNPs showed slightly increased whiteline intensity compared to that of Pt foil. When Au was deposited together with Pt, the resonance peaks of the NPs were slightly, but systematically shifted due to the formation of Pt-Au alloy.

The interaction between SnO2 and substrate in SnO2 nanoparicles (NPs)-carbon nanotubes (CNTs) composite has been studied by X-ray absorption near-edge structures (XANES) at Sn M-5,M-4, O K-edge and C K-edge. SnO2 NPS in the composite have a rutile crystal structure with abundant surface states. The variation in resonance features of the XANES strongly supports that the crystalline SnO2 NPs interact with CNTs through synergic bonding involving charge redistribution between C 2p-derived states and the valence and conduction bands in SnO2 NPs via interaction at the interface facilitated by oxidation treatment of the CNT prior to composite formation. Raman and ultraviolet photoelectron spectroscopy (UPS) results support the synergic bonding interaction. Such interaction is expected not only to immobilize SnO2 NPs on CNT but also to improve the conductivity of SnO2 NPs.

X-ray excited optical luminescence (XEOL) and x-ray absorption near-edge structure in total electron, x-ray fluorescence, and photoluminescence yields at Sn M5,4-, O K-, and Sn K-edges have been used to study the luminescence from SnO2 nanoribbons. The effect of the surface on the luminescence from SnO2 nanoribbons was studied by preferential excitation of the ions in the near-surface region and at the normal lattice positions, respectively. No noticeable change of luminescence from SnO2 nanoribbons was observed if the Sn ions in the near-surface region were excited selectively, while the luminescence intensity changes markedly when Sn or O ions at the normal lattice positions were excited across the corresponding edges. Based on the experimental results, we show that the luminescence from SnO2 nanoribbons is dominated by energy transfer from the excitation of the whole SnO2 lattice to the surface states. Surface site specificity is not observable due to its low concentration and weak absorption coefficient although the surface plays an important role in the emission as a luminescence center. The energy transfer and site specificity of the XEOL or the lack of the site specificity from a single-phase sample is discussed.

X‐ray excited optical luminescence (XEOL) is a well established technique to study nano structured light emitting materials. XEOL bares the essential features necessary for the study of advanced nano structured materials like element specifity, good quantum efficiency, and easy approach for time resolution. Being sensitive to the geometry of the material on a nano‐scale, luminescence gives insight into the phenomenologic correlation of structural, optical, and electronic properties. Besides structural aspects we study the time behavior of nanostructured ZnO (Eu) in a pump‐probe like experiment, using the time structure of synchrotron radiation.

We present an experimental technique using the time structure of synchrotron radiation to study time resolved X-ray excited optical luminescence. In particular we are taking advantage of the bunched distribution of electrons in a synchrotron storage ring, giving short x-ray pulses (10-10(2) picoseconds) which are separated by non-radiating gaps on the nano- to tens of nanosecond scale - sufficiently wide to study a broad range of optical decay channels observed in advanced nanostructured materials.