111 research outputs found
Microstructure of horseshoe nails using neutron diffraction
Neutron diffraction allows non-destructive testing of the bulk microstructure of
mechanical components. The microstructures of horseshoe nails made through three different
processes have been explored as a function of position along the nail. Despite all nails being
made of similar plain low carbon steel and being process annealed after manufacture, the
microstructures are far from the same. Nails made from strip, using a cold forging stamping
process, show narrower diffraction peaks indicating a narrower distribution of lattice
parameters and also show diffraction peak intensity ratios closer to those expected for
unstrained steel. Thus the distribution of the orientation of grains in these nails is closer to
that of undistorted steel compared to nails made through the other two processes considered â
one a drawing from wire, the other a combination of rolling and cold forging. The blades of
the drawn nails showed little preferred orientation but the converse was true in the heads.
Differing patterns of preferred orientation suggest that the various manufacturing approaches
result in substantially different mechanical advantages for the three types of nails, a result in
accord with mechanical testing
Exact location of dopants below the Si(001):H surface from scanning tunnelling microscopy and density functional theory
Control of dopants in silicon remains the most important approach to
tailoring the properties of electronic materials for integrated circuits, with
Group V impurities the most important n-type dopants. At the same time, silicon
is finding new applications in coherent quantum devices, thanks to the
magnetically quiet environment it provides for the impurity orbitals. The
ionization energies and the shape of the dopant orbitals depend on the surfaces
and interfaces with which they interact. The location of the dopant and local
environment effects will therefore determine the functionality of both future
quantum information processors and next-generation semiconductor devices. Here
we match observed dopant wavefunctions from low-temperature scanning tunnelling
microscopy (STM) to images simulated from first-principles density functional
theory (DFT) calculations. By this combination of experiment and theory we
precisely determine the substitutional sites of neutral As dopants between 5
and 15A below the Si(001):H surface. In the process we gain a full
understanding of the interaction of the donor-electron state with the surface,
and hence of the transition between the bulk dopant (with its delocalised
hydrogenic orbital) and the previously studied dopants in the surface layer.Comment: 12 pages; accepted for publication in Phys. Rev.
Spin-gap opening accompanied by a strong magnetoelastic response in the S=1 magnetic dimer system Ba3BiRu2O9
Neutron diffraction, magnetization, resistivity, and heat capacity
measurements on the 6H-perovskite Ba3BiRu2O9 reveal simultaneous magnetic and
structural dimerization driven by strong magnetoelastic coupling. An
isostructural but strongly displacive first-order transition on cooling through
T*=176 K is associated with a change in the nature of direct Ru-Ru bonds within
Ru2O9 face-sharing octahedra. Above T*, Ba3BiRu2O9 is an S=1 magnetic dimer
system with intradimer exchange interactions J0/kB=320 K and interdimer
exchange interactions J'/kB=-160 K. Below T*, a spin-gapped state emerges with
\Delta\approx220 K. Ab initio calculations confirm antiferromagnetic exchange
within dimers, but the transition is not accompanied by long range-magnetic
order.Comment: 5 pages, 5 figures, accepted by Physical Review
Microstructure and texture analysis of ÎŽ-hydride precipitation in Zircaloy-4 materials by electron microscopy and neutron diffraction
This work presents a detailed microstructure and texture study of various hydrided Zircaloy-4 materials by neutron diffraction and microscopy. The results show that the precipitated ÎŽ-ZrH1.66 generally follows the ÎŽ (111) //α (0001) and ÎŽ[]//α[] orientation relationship with the α-Zr matrix. The ÎŽ-hydride displays a weak texture that is determined by the texture of the α-Zr matrix, and this dependence essentially originates from the observed orientation correlation between α-Zr and ÎŽ-hydride. Neutron diffraction line profile analysis and high-resolution transmission electron microscopy observations reveal a significant number of dislocations present in the ÎŽ-hydride, with an estimated average density one order of magnitude higher than that in the α-Zr matrix, which contributes to the accommodation of the substantial misfit strains associated with hydride precipitation in the α-Zr matrix. The present observations provide an insight into the behaviour of ÎŽ-hydride precipitation in zirconium alloys and may help with understanding the induced embrittling effect of hydrides.Fil: Wang, Zhiyang. University of Wollongong; Australia. Australian Nuclear Science and Technology Organisation; AustraliaFil: Garbe, Ulf. Australian Nuclear Science and Technology Organisation; AustraliaFil: Li, Huijun. University of Wollongong; AustraliaFil: Wang, Yanbo. University of Sydney; AustraliaFil: Studer, Andrew J.. Australian Nuclear Science and Technology Organisation; AustraliaFil: Sun, Guangai. Institute of Nuclear Physics and Chemistry, CAEP; ChinaFil: Harrison, Robert P.. Australian Nuclear Science and Technology Organisation, Institute of Materials Engineering; AustraliaFil: Liao, Xiaozhou. University of Sydney; AustraliaFil: Vicente Alvarez, Miguel Angel. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Ărea de EnergĂa Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Santisteban, Javier Roberto. ComisiĂłn Nacional de EnergĂa AtĂłmica. Gerencia del Ărea de EnergĂa Nuclear. Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; ArgentinaFil: Kong, Charlie. University of New South Wales; Australi
Collapse and reappearance of magnetic orderings in spin frustrated TbMnO3 induced by Fe substitution
We studied the temperature dependent magnetic phase evolution in spin frustrated TbMnO3 affected by Fe doping via powder neutron diffraction. With the introduction of Fe (10% and 20%), the long range incommensurate magnetic orderings collapse. When the Fe content is increased to 30%, a long-range antiferromagnetic ordering develops, while a spin reorientation transition is found near 35âK from a canted G-type antiferromagnetic ordering to a collinear G-type antiferromagnetic ordering. This work demonstrates the complex magnetic interactions existing in transition metal oxides, which helps to understand the frustrated spin states in other similar systems and design magnetic materials as well
Critical role of the coupling between the octahedral rotation and A-site ionic displacements in PbZrO3-based antiferroelectric materials investigated by in situ neutron diffraction
This in situ neutron-diffraction study on antiferroelectric (AFE) Pb0.99(Nb0.02Zr0.65Sn0.28Ti0.05)O3 polycrystalline materials describes systematic structural and associated preferred orientation changes as a function of
applied electric field and temperature. It is found that the pristine AFE phase can be poled into the metastable
ferroelectric (FE) phase at room temperature. At this stage, both AFE and FE phases consist of modes associated
with octahedral rotation and A-site ionic displacements. The temperature-induced phase transition indicates that
the octahedral rotation and ionic displacements are weakly coupled in the room-temperature FE phase and
decoupled in the high-temperature FE phase. However, both temperature and E-field-induced phase transitions
between the AFE and high-temperature FE phase demonstrate the critical role of coupling between octahedral
rotation and A-site ionic displacements in stabilizing the AFE structure, which provides not only experimental
evidence to support previous theoretical calculations, but also an insight into the design and development of AFE
materials. Moreover, the associated preferred orientation evolution in both AFE and FE phases is studied during
the phase transitions. It is found that the formation of the preferred orientation can be controlled to tune the
samplesâ FE and AFE properties.T.L., Y.L., and R.L.W. thank the Australian Research
Council (ARC DP160104780) for financial support in the form
of a joint ARC Discovery Project. Y.L. also acknowledges the
ARCâs support in the form of an ARC Future Fellowship.
The authors also thank the Australian Nuclear Science and
Technology Organisation for support in the form of beam time
High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs
Tetragonal CuMnAs was the first antiferromagnet where reorientation of the
N\'eel vector was reported to occur by an inverse spin galvanic effect. A
complicating factor in the formation of phase-pure tetragonal CuMnAs is the
formation of an orthorhombic phase with nearly the same stoichiometry.
Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to
maintain a single phase in traditional solid state synthesis reactions. Here we
show that subtle differences in diffraction patterns signal pervasive
inhomogeneity and phase separation, even in Cu-rich CuMnAs.
From calorimetry and magnetometry measurements, we identify two transitions
corresponding to the N\'eel temperature (T) and an antiferromagnet to weak
ferromagnet transition in CuMnAs and
CuMnAs. These transitions have clear crystallographic
signatures, directly observable in the lattice parameters upon in-situ heating
and cooling. The immiscibility and phase separation could arise from a
spinoidal decomposition that occurs at high temperatures, and the presence of a
ferromagnetic transition near room temperature warrants further investigation
of its effect on the electrical switching behavior.Comment: 10 pages, 9 figures, added author middle initia
Characterization of the Prokaryotic Sodium Channel NavSp Pore with a Microfluidic Bilayer Platform
This paper describes the use of a newly-developed micro-chip bilayer platform to examine the electrophysiological properties of the prokaryotic voltage-gated sodium channel pore (NavSp) from Silicibacter pomeroyi. The platform allows up to 6 bilayers to be analysed simultaneously. Proteoliposomes were incorporated into suspended lipid bilayers formed within the microfluidic bilayer chips. The chips provide access to bilayers from either side, enabling the fast and controlled titration of compounds. Dose-dependent modulation of the opening probability by the channel blocking drug nifedipine was measured and its IC50 determined
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