Chalk River Laboratories

About: Chalk River Laboratories is a based out in . It is known for research contribution in the topics: Neutron diffraction & Neutron scattering. The organization has 2297 authors who have published 2700 publications receiving 73287 citations.

Spin-glass behavior in the S = 1 / 2 fcc ordered perovskite Sr 2 CaReO 6

Abstract: The ordered perovskite ${\mathrm{Sr}}_{2}{\mathrm{CaReO}}_{6}$ of monoclinic symmetry [space group ${P2}_{1}/n,a=5.7556(3)\AA{},b=5.8534(3)\AA{},c=8.1317(4)\AA{},\ensuremath{\beta}=90.276(5)\ifmmode^\circ\else\textdegree\fi{}$ at $T=4\mathrm{K}$] has been synthesized using standard solid-state chemistry techniques. The difference in the size and charge of the cations induces an ordering of the B site ${\mathrm{Ca}}^{2+}$ and ${\mathrm{Re}}^{6+}$ ions which leads to a distorted fcc lattice of spin-$\frac{1}{2}$ ${\mathrm{Re}}^{6+}$ ${(5d}^{1})$ moments. dc magnetic susceptibility measurements indicate a maximum at ${T}_{G}\ensuremath{\sim}14\mathrm{K}$ and an irreversibility in the field-cooled and zero-field-cooled data at \ensuremath{\sim}22 K that is believed to be caused by the geometric frustration inherent in the fcc structure. Neutron-scattering measurements confirm the absence of magnetic long-range order, and muon spin relaxation experiments indicate the presence of an abrupt spin freezing at ${T}_{G}.$ Specific heat measurements reveal a broad anomaly typical of spin glasses and no sharp feature. 65% of the spin entropy is released at low temperatures. The low-temperature data do not show the expected linear temperature dependence, but rather a ${T}^{3}$ relationship, as is observed, typically, for antiferromagnetic spin waves. The material is characterized as an unconventional, essentially disorder-free, spin glass.

Three-dimensional imaging of dislocation dynamics during the hydriding phase transformation

Abstract: Crystallographic imperfections significantly alter material properties and their response to external stimuli, including solute-induced phase transformations. Despite recent progress in imaging defects using electron and X-ray techniques, in situ three-dimensional imaging of defect dynamics remains challenging. Here, we use Bragg coherent diffractive imaging to image defects during the hydriding phase transformation of palladium nanocrystals. During constant-pressure experiments we observe that the phase transformation begins after dislocation nucleation close to the phase boundary in particles larger than 300 nm. The three-dimensional phase morphology suggests that the hydrogen-rich phase is more similar to a spherical cap on the hydrogen-poor phase than to the core–shell model commonly assumed. We substantiate this using three-dimensional phase field modelling, demonstrating how phase morphology affects the critical size for dislocation nucleation. Our results reveal how particle size and phase morphology affects transformations in the PdH system. Coherent diffractive imaging during hydriding of palladium nanocrystals reveals that phase nucleation begins after dislocation nucleation at the phase boundary for large particles. The hydrogen-rich phase resembles a spherical cap.

On the influence of crystal elastic moduli on computed lattice strains in AA-5182 following plastic straining

Abstract: Crystal lattice plane spacing is modified by the application of stress. The changes in spacing can be measured with neutron diffraction and used to determine the elastic strains in loaded crystals. Using finite element methods, elastic strains can be computed under loading that mimics the experiment. The quality of comparisons between the measured and computed strains depends strongly on accurate knowledge of parameters that quantify the single crystal elastic and plastic responses. For one aluminum alloy in particular, we have found that we can improve the match of lattice strains through careful choice of the single crystal elastic moduli. The parameters are selected on the basis of comparisons between the experimental results and a series of simulations in which the single crystal moduli were varied systematically. Good correspondence is obtained for a set of moduli with higher single crystal anisotropy than those of pure aluminum.