Carbides / High pressures and temperatures / Synchrotron radiation / Analytical electron microscopy / Density functional theory (DFT) / X-ray diffraction / Powder diffraction structure analysis Abstract. A combined X-ray diffraction, EELS and DFT study of the reaction of rhenium with carbon at high-(P, T ) conditions up to P max ¼ 67 GPa and T max ¼ 3800 K is presented. A hexagonal rhenium carbide, ReC x , was identified as the stable phase at high-(P, T ) conditions. A composition of ReC 0:5 is proposed. No evidence for a cubic ReC polymorph with rocksalt structure, as suggested in the literature, or for any other phase was found at the P-T conditions explored. A preliminary P-T rhenium-carbon phase diagram has been derived and properties such as bulk moduli and elastic stiffness coefficients were obtained.

The electrochemical reaction behavior of a commercial Li-ion battery (LiFePO4-based cathode, graphite-based anode) has been measured via in situ neutron diffraction. A multivariate analysis was successfully applied to the neutron diffraction data set facilitating in the determination of Li bearing phases participating in the electrochemical reaction in both the anode and cathode as a function of state-of-charge (SOC). The analysis resulted in quantified phase fraction values for LiFePO4 and FePO4 cathode compounds as well as the identification of staging behavior of Li6, Li12, Li24, and graphite phases in the anode. An additional Li-graphite phase has also been tentatively identified during electrochemical cycling as LiC48 at conditions of ∼5% to 15% SOC.

State‐of‐the‐art neutron time‐of‐flight diffractometers at modern neutron sources allow sample throughput at rates of much less than one hour per sample. Automated sample changes with a high degree of reliability and flexibility are essential to assure safe operation and efficient use of available neutron flux. At the High‐Pressure Preferred Orientation (HIPPO) diffractometer, a previous sample changer measured over 2300 texture and 400 powder samples at ambient conditions to study the properties of crystalline materials at the Lujan neutron scattering facility at the Los Alamos Neutron Science Center. Experience gained during operation of the sample changer for over a decade showed room for improvement and led to a new design using current industrial robot technology. Here, the new HIPPO versatile six‐axis robotic sample changer for neutron powder diffraction experiments including texture measurements is presented.

We studied the phase-transition induced texture changes and strengthening mechanism for zirconium metal under quasi-hydrostatic compression and uni-axial deformation under confined high pressure using the deformation-DIA (D-DIA) apparatus. It is shown that the experimentally obtained texture for ω-phase Zr can be qualitatively described by combining a subset of orientation variants previously proposed in two different models. The determined flow stress for the high-pressure ω-phase is 0.5–1.2 GPa, more than three times higher than that of the α-phase. Using first-principles calculations, we investigated the mechanical and electronic properties of the two Zr polymorphs. We find that the observed strengthening can be attributed to the relatively strong directional bonding in the ω phase, which significantly increases its shear plastic resistance over the α-phase Zr. The present findings provide an alternate route for Zr metal strengthening by high-pressure phase transformation.

A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 °C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80° around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure - Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 °C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility.

An automated sample changer with an Eulerian cradle for neutron texture measurements is described. This device has been measuring over 2300 texture and almost 400 powder samples at ambient conditions since it became operational in 2002 for use in the high pressure-preferred orientation diffractometer at the LANSCE neutron scattering facility. Operation for almost a decade resulted in sustained enhancements of mechanics, electronics, and software which significantly improved reliability and resiliency. We also describe in this paper our platform independent computer program POD2K which we use to create publication quality pole figure plots for texture samples.

In situ deformation studies of polycrystalline materials using diffraction are an established method to understand elastic and plastic deformation of materials. Studies of active deformation mechanisms, the interplay of deformation with texture, and ultimately the development of predictive capabilities for deformation modeling are an active field of research. Parameters studied by diffraction are typically lattice strains and texture evolution, which coupled with the macroscopic flow curve allow for improved understanding of the micro-mechanics of deformation. We performed a study of the uniaxial deformation of Zircaloy-2 at 2 GPa at the 13-BM-D beamline at the Advanced Photon Source. The deformation-DIA apparatus generates a confining hydrostatic pressure using a cubic anvil setup. Two differential rams allow an increase (compressive load) or decrease (tensile load) of the uniaxial straining in the vertical direction, allowing studies of plastic deformation at high pressures. In this paper, we describe how macroscopic strains, hydrostatic pressure, and uniaxial strains are derived and present some brief results.

We investigated the formation of UCx from UO2+x and graphite in situ using neutron diffraction at high temperatures with particular focus on resolving the conflicting reports on the crystal structure of non-quenchable cubic UC2. The agents were UO2 nanopowder, which closely imitates nano grains observed in spent reactor fuels, and graphite powder. In situ neutron diffraction revealed the onset of the UO2 + 2C  UC + CO2 reaction at 1440˚C, with its completion at 1500˚C. Upon further heating, carbon diffuses into the uranium carbide forming C2 groups at the octahedral sites. This resulting high temperature cubic UC2 phase is similar to the NaCl-type structure as proposed by Bowman et al. Our novel experimental data provide insights into the mechanism and kinetics of formation of UC as well as characteristics of the high