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46 items found (0 items not approved), displaying 11 to 20.[First/Prev] 1, 2, 3, 4, 5 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I12-JEEP: Joint Engineering, Environmental and Processing	Transition from high-entropy to Cu-based (TiZrNbNi)1−xCux metallic glasses Ramir Ristić , Ignacio A. Figueroa , Andrea Lachova , Stefan Michalik , Vesna Mikšić Trontl , Petar Pervan , Krešo Zadro , Damir Pajić , Emil Babić Journal Of Applied Physics 126 DOI: 10.1063/1.5119373 Diamond Proposal Number(s): [21642] Show Abstract ▼ Abstract: A study of a transition from conventional multicomponent alloys to high-entropy alloys (HEAs) is important both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of conventional alloys. We report the main result of such a study performed on (TiZrNbNi)1−xCux metallic glasses (MG) over a broad concentration range x ≤ 0.52 encompassing both high entropy-MGs and Cu-based MGs. A comprehensive study of the composition, homogeneity, thermal stability, atomic structure, electronic structure, and magnetic susceptibility of 11 alloys has been performed. Thermal analysis revealed a rather weak variation of thermal parameters and glass forming ability with x. The study of the atomic structure showed a linear variation of average interatomic distances and atomic volumes close to those predicted by Vegard’s law. The coordination numbers and atomic packing fractions were constant throughout the explored concentration range. The electronic density of states (DOS) showed a split-band structure with DOS close to the Fermi level dominated with d-states of Ti, Zr, and Nb. Accordingly, magnetic susceptibility decreased linearly with x and extrapolated to that of Cu. Thus, the studied alloys show ideal solution behavior similar to that of binary Cu-Ti, Zr, and Hf MGs. The results are compared with those for (TiZrNbCu)1−xNix MGs and (CrMnFeCo)1−xNix alloys and their impact on understanding the transition from high-entropy-MGs to conventional MGs with the same composition is briefly discussed.	Oct 2019
I11-High Resolution Powder Diffraction	The structure and thermoelectric properties of tungsten bronze Ba6Ti2Nb8O30 Dongting Jiang , Dursun Ekren , Feridoon Azough , Sarah Day , Kan Chen , Amit Mahajan , Demie M. Kepaptsoglou , Quentin M. Ramasse , Michael J. Reece , Robert Freer Journal Of Applied Physics 126 DOI: 10.1063/1.5119962 Open Access Show Abstract ▼ Abstract: Tungsten bronze (TB) structured materials have attracted attention as possible thermoelectrics because of their complex crystal structure. In this work, a new thermoelectric ceramic with a tetragonal tungsten bronze (TB) structure, Ba6Ti2Nb8O30 (BTN), was prepared by the conventional mixed oxide route with some samples processed by Spark Plasma Sintering (SPS). The addition of MnO enabled the fabrication of high density BTN ceramics at a low sintering temperature of 1580 K in air and by SPS. All samples were annealed in a reducing atmosphere after sintering. X-ray diffraction showed that Ba6Ti2Nb8O30 crystallizes with tetragonal symmetry (P4bm space group). High angle annular dark field-electron energy loss spectroscopy analysis confirmed the proposed crystal structure and provided exact elemental distributions in the lattice, showing higher concentrations of Ti in the 2b lattice sites compared to the 8d lattice sites. XPS showed the presence of two spin-orbit double peaks at 207.7 eV in the reduced BTN samples, confirming the presence of Nb4+ ions. By the use of a sintering aid and optimization of the processing parameters, the ceramics achieved a high power factor of 280 μW/m K2 at 873 K. The BTN ceramics showed phonon-glass-type thermal conduction behavior with a low thermal conductivity of 1.7–1.65 W/m K at 300–873 K. A thermoelectric figure of merit (ZT) of 0.14 was achieved at 873 K. This ZT value is comparable with results for many TB thermoelectrics. However, BTN has the advantage of much easier processing.	Sep 2019
I11-High Resolution Powder Diffraction	Mapping the structural transitions controlled by the trilinear coupling in Ca3-xSrxTi2O7 Marie Kratochvilova , Fei-Ting Huang , Maria-Teresa Fernandez Diaz , Milan Klicpera , Sarah Day , Stephen P. Thompson , Yoon-Seok Oh , Bin Gao , Sang-Wook Cheong , Je-Geun Park Journal Of Applied Physics 125 DOI: 10.1063/1.5089723 Diamond Proposal Number(s): [16074] Show Abstract ▼ Abstract: We present the results of the high-temperature neutron and x-ray diffraction experiments on the Ca3–xSrxTi2O7 (x = 0.5, 0.8, 0.85, 0.9) compounds. The ferro- to paraelectric transition in these hybrid improper ferroelectric materials arises from the so-called trilinear coupling. Depending on the strontium content, various structures and phase transitions, different from theoretical predictions, emerge. The in situ x-ray powder diffraction indicates a direct ferro- to paraelectric transition between the orthorhombic A21am and the tetragonal undistorted I4/mmm phase for x ≤ 0.6. We identified a reduction in the trilinear coupling robustness by increasing the Sr-doping level to lead to the emergence of the intermediate tetragonal P42/mnm phase and the gradual suppression of the orthorhombic phase. The observed character of the structure transitions and the Ca3–xSrxTi2O7 phase diagram are discussed in the framework of theoretical models of other related hybrid improper ferroelectric systems.	Jun 2019
I09-Surface and Interface Structural Analysis	Cooperative effects of strain and electron correlation in epitaxial VO2 and NbO2 Wei-Cheng Lee , Matthew Wahila , Shantanu Mukherjee , Christopher N. Singh , Tyler Eustance , Anna Regoutz , Hanjong Paik , Jos E. Boschker , Fanny Rodolakis , Tien-Lin Lee , Darrell G. Schlom , Louis F. J. Piper Journal Of Applied Physics 125 DOI: 10.1063/1.5052636 Diamond Proposal Number(s): [20647, 21430] Show Abstract ▼ Abstract: We investigate the electronic structure of epitaxial VO 2 2 films in the rutile phase using density functional theory combined with the slave-spin method (DFT + SS). In DFT + SS, multi-orbital Hubbard interactions are added to a DFT-fit tight-binding model, and slave spins are used to treat electron correlations. We find that while stretching the system along the rutile c c -axis results in a band structure favoring anisotropic orbital fillings, electron correlations favor equal filling of the t 2g t2g orbitals. These two distinct effects cooperatively induce an orbital-dependent redistribution of the electron occupations and spectral weights, driving strained VO 2 2 toward an orbital selective Mott transition (OSMT). The simulated single-particle spectral functions are directly compared to V L-edge resonant X-ray photoemission spectroscopy of epitaxial 10 nm VO 2 2 /TiO 2 2 (001) and (100) strain orientations. Excellent agreement is observed between the simulations and experimental data regarding the strain-induced evolution of the lower Hubbard band. Simulations of rutile NbO 2 2 under similar strain conditions are performed, and we predict that an OSMT will not occur in rutile NbO 2 2 . Our prediction is supported by the high-temperature hard x-ray photoelectron spectroscopy measurement on relaxed NbO 2 2 (110) thin films with no trace of the lower Hubbard band. Our results indicate that electron correlations in VO 2 2 are important and can be modulated even in the rutile phase before the Peierls instability sets in.	Feb 2019
B18-Core EXAFS	Extended X-ray absorption fine structure study of the Er bonding in AlNO:Er x films with x ≤ 3.6% M. Katsikini , V. Kachkanov , P. Boulet , P. R. Edwards , K. P. O'Donnell , V. Brien Journal Of Applied Physics 124 DOI: 10.1063/1.5036614 Diamond Proposal Number(s): [9370] Show Abstract ▼ Abstract: The structural properties of Er-doped AlNO epilayers grown by radio frequency magnetron sputtering were studied by Extended X-ray Absorption Fine Structure spectra recorded at the Er L3 edge. The analysis revealed that Er substitutes for Al in all the studied samples, and the increase in the Er concentration from 0.5 to 3.6 at. % is not accompanied by the formation of ErN, Er2O3, or Er clusters. Simultaneously recorded X-ray Absorption Near Edge Structure spectra verify that the bonding configuration of Er is similar in all studied samples. The Er-N distance is constant at 2.18–2.19 Å, i.e., approximately 15% larger than the Al-N bond length, revealing that the introduction of Er in the cation sublattice causes a considerable local distortion. The Debye-Waller factor, which measures the static disorder of the second nearest shell of Al neighbors, has a local minimum for the sample containing 1% Er that coincides with the highest photoluminescence efficiency of the sample set.	Aug 2018
	Simulations of x-ray speckle-based dark-field and phase-contrast imaging with a polychromatic beam Marie-Christine Zdora , Pierre Thibault , Franz Pfeiffer , Irene Zanette Journal Of Applied Physics 118 (11) DOI: 10.1063/1.4931145 Open Access Show Abstract ▼ Abstract: Following the first experimental demonstration of x-ray speckle-based multimodal imaging using a polychromatic beam [I. Zanette et al ., Phys. Rev. Lett. 112(25), 253903 (2014)], we present a simulation study on the effects of a polychromatic x-ray spectrum on the performance of this technique. We observe that the contrast of the near-field speckles is only mildly influenced by the bandwidth of the energy spectrum. Moreover, using a homogeneous object with simple geometry, we characterize the beam hardening artifacts in the reconstructed transmission and refraction angle images, and we describe how the beam hardening also affects the dark-field signal provided by speckle tracking. This study is particularly important for further implementations and developments of coherent speckle-based techniques at laboratory x-ray sources.	Sep 2015
I10-Beamline for Advanced Dichroism - scattering	X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100) W. Q. Liu , M. Y. Song , N. J. Maltby , S. P. Li , J. G. Lin , M. G. Samant , S. S. P. Parkin , P. Bencok , P. Steadman , A Dobrynin , Y. B. Xu , R. Zhang Journal Of Applied Physics 117 DOI: 10.1063/1.4916296 Show Abstract ▼ Abstract: The spin and orbital magnetic moments of the Fe3O4 epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ B/f.u., which is ∼70% of that for the bulk-like Fe3O4. A significant unquenched orbital moment up to 0.54 ± 0.05 μ B/f.u. was observed, which could come from the symmetry breaking at the Fe3O4/MgO interface. Such sizable orbital moment will add capacities to the Fe3O4-based spintronics devices in the magnetization reversal by the electric field.	May 2015
B16-Test Beamline Metrology Optics Theoretical Physics	Theoretical analysis of the background intensity distribution in X-ray Birefringence Imaging using synchrotron bending-magnet radiation John Sutter , Igor Dolbnya , Steve Collins , Kenneth D. M. Harris , Gregory Edwards-Gau , Benjamin Palmer Journal Of Applied Physics 117 (16), 164902 DOI: 10.1063/1.4918925 Diamond Proposal Number(s): [8323] Open Access Show Abstract ▼ Abstract: In the recently developed technique of X-ray Birefringence Imaging, molecular orientational order in anisotropic materials is studied by exploiting the birefringence of linearly polarized X-rays with energy close to an absorption edge of an element in the material. In the experimental setup, a vertically deflecting high-resolution double-crystal monochromator is used upstream from the sample to select the appropriate photon energy, and a horizontally deflecting X-ray polarization analyzer, consisting of a perfect single crystal with a Bragg reflection at Bragg angle of approximately 45°, is placed downstream from the sample to measure the resulting rotation of the X-ray polarization. However, if the experiment is performed on a synchrotron bending-magnet beamline, then the elliptical polarization of the X-rays out of the electron orbit plane affects the shape of the output beam. Also, because the monochromator introduces a correlation between vertical position and photon energy to the X-ray beam, the polarization analyzer does not select the entire beam, but instead selects a diagonal stripe, the slope of which depends on the Bragg angles of the monochromator and the polarization analyzer. In the present work, the final background intensity distribution is calculated analytically because the phase space sampling methods normally used in ray traces are too inefficient for this setup. X-ray Birefringence Imaging data measured at the Diamond Light Source beamline B16 agree well with the theory developed here.	Apr 2015
I15-Extreme Conditions	High-pressure structural and elastic properties of Tl2O3 O. Gomis , D. Santamaria-Perez , Javier Ruiz Fuertes , Juan Angel Sans Tresserras , R. Vilaplana , H. M. Ortiz , B. Garcia-Domene , Javi Manjon Herrera , Daniel Errandonea , P. Rodriguez-Hernandez , A. Munoz , M. Mollar Journal Of Applied Physics 116 (13), 133521-1 133521-9 DOI: 10.1063/1.4897241 Diamond Proposal Number(s): [6517] Show Abstract ▼ Abstract: The structural properties of Thallium (III) oxide (Tl2O3) have been studied both experimentally and theoretically under compression at room temperature. X-ray powder diffraction measurements up to 37.7 GPa have been complemented with ab initio total-energy calculations. The equation of state of Tl2O3 has been determined and compared to related compounds. It has been found experimentally that Tl2O3 remains in its initial cubic bixbyite-type structure up to 22.0 GPa. At this pressure, the onset of amorphization is observed, being the sample fully amorphous at 25.2 GPa. The sample retains the amorphous state after pressure release. To understand the pressure-induced amorphization process, we have studied theoretically the possible high-pressure phases of Tl2O3. Although a phase transition is predicted at 5.8 GPa to the orthorhombic Rh2O3-II-type structure and at 24.2 GPa to the orthorhombic a-Gd2S3-type structure, neither of these phases were observed experimentally, probably due to the hindrance of the pressure-driven phase transitions at room temperature. The theoretical study of the elastic behavior of the cubic bixbyite-type structure at high-pressure shows that amorphization above 22 GPa at room temperature might be caused by the mechanical instability of the cubic bixbyite-type structure which is theoretically predicted above 23.5 GPa.	Oct 2014
	Nanoscale structural heterogeneity in Ni-rich half-Heusler TiNiSn Jason E. Douglas , Philip Chater , Craig M. Brown , Tresa M. Pollock , Ram Seshadri Journal Of Applied Physics 116 DOI: 10.1063/1.4900497 Show Abstract ▼ Abstract: The structural implications of excess Ni in the TiNiSn half-Heusler compound are examined through a combination of synchrotron x-ray and neutron scattering studies, in conjunction with first principles density functional theory calculations on supercells. Despite the phase diagram suggesting that TiNiSn is a line compound with no solid solution, for small x in TiNi1+ x Sn there is indeed an appearance—from careful analysis of the scattering—of some solubility, with the excess Ni occupying the interstitial tetrahedral site in the half-Heusler structure. The analysis performed here would point to the excess Ni not being statistically distributed, but rather occurring as coherent nanoclusters. First principles calculations of energetics, carried out using supercells, support a scenario of Ni interstitials clustering, rather than a statistical distribution.	Oct 2014

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