Novel experimental setup for megahertz X-ray diffraction in a diamond anvil cell at the High Energy Density (HED) instrument of the European X-ray Free-Electron Laser (EuXFEL).

The high-precision X-ray diffraction setup for work with diamond anvil cells (DACs) in interaction chamber 2 (IC2) of the High Energy Density instrument of the European X-ray Free-Electron Laser is described. This includes beamline optics, sample positioning and detector systems located in the multipurpose vacuum chamber. Concepts for pump-probe X-ray diffraction experiments in the DAC are described and their implementation demonstrated during the First User Community Assisted Commissioning experiment. X-ray heating and diffraction of Bi under pressure, obtained using 20 fs X-ray pulses at 17.8 keV and 2.2 MHz repetition, is illustrated through splitting of diffraction peaks, and interpreted employing finite element modeling of the sample chamber in the DAC.

The phase diagram of Ti-6Al-4V at high-pressures and high-temperatures.

We report results from a series of diamond-anvil-cell synchrotron x-ray diffraction and large-volume-press experiments, and calculations, to investigate the phase diagram of commercial polycrystalline high-strength Ti-6Al-4V alloy in pressure-temperature space. Up to ∼30 GPa and 886 K, Ti-6Al-4V is found to be stable in the hexagonal-close-packed, orαphase. The effect of temperature on the volume expansion and compressibility ofα-Ti-6Al-4V is modest. The martensiticα→ω(hexagonal) transition occurs at ∼30 GPa, with both phases coexisting until at ∼38-40 GPa the transition to theωphase is completed. Between 300 K and 844 K theα→ωtransition appears to be independent of temperature.ω-Ti-6Al-4V is stable to ∼91 GPa and 844 K, the highest combined pressure and temperature reached in these experiments. Pressure-volume-temperature equations-of-state for theαandωphases of Ti-6Al-4V are generated and found to be similar to pure Ti. A pronounced hysteresis is observed in theω-Ti-6Al-4V on decompression, with the hexagonal structure reverting back to theαphase at pressures below ∼9 GPa at room temperature, and at a higher pressure at elevated temperatures. Based on our data, we estimate the Ti-6Al-4Vα-ß-ωtriple point to occur at ∼900 K and 30 GPa, in good agreement with our calculations.

Subnanosecond phase transition dynamics in laser-shocked iron.

Iron is one of the most studied chemical elements due to its sociotechnological and planetary importance; hence, understanding its structural transition dynamics is of vital interest. By combining a short pulse optical laser and an ultrashort free electron laser pulse, we have observed the subnanosecond structural dynamics of iron from high-quality x-ray diffraction data measured at 50-ps intervals up to 2500 ps. We unequivocally identify a three-wave structure during the initial compression and a two-wave structure during the decaying shock, involving all of the known structural types of iron (α-, γ-, and ε-phase). In the final stage, negative lattice pressures are generated by the propagation of rarefaction waves, leading to the formation of expanded phases and the recovery of γ-phase. Our observations demonstrate the unique capability of measuring the atomistic evolution during the entire lattice compression and release processes at unprecedented time and strain rate.

Effects of a finger exercise program on hand function in automobile workers with hand osteoarthritis: A randomized controlled trial.

Hand osteoarthritis reduces a person's ability to perform work activities and return to their occupation. We investigated the effects of a finger exercise program on hand grip strength, pain, physical function, and stiffness in automobile manufacturing workers with hand osteoarthritis. This randomized controlled trial was conducted on 29 subjects. Fifteen experimental subjects received a finger exercise program with paraffin baths, while 14 control subjects received only paraffin baths. Hand grip strength, pain, physical function, and stiffness were assessed at baseline and 8 weeks later. In the experimental group, hand grip strength (P < 0.001) and Australian/Canadian osteoarthritis hand index (AUSCAN) scores (pain, P < 0.001; stiffness, P < 0.001; physical function, P < 0.001) were significantly improved by 3.52 ± 2.03, 21.6 ± 8.3 (pain), 16.8 ± 10.21 (stiffness), and 13.86 ± 4.54 (physical function) compared with preintervention values. In the control group, hand grip strength (P = 0.004) and AUSCAN scores (pain, P < 0.001; stiffness, P = 0.019; physical function, P < 0.001) were significantly improved by 0.57 ± 0.62, 7.85 ± 5.46 (pain) 11.42 ± 7.18 (stiffness), and 10.28 ± 14.41 (physical function) compared with preintervention values. Significant differences between groups were found for postintervention hand grip strength (P = 0.015) and AUSCAN index subscale scores (pain, P < 0.001; physical function, P = 0.020). A combined finger exercise and paraffin bath program is effective in reducing pain, improving physical function, and increasing hand grip strength in workers with hand osteoarthritis.

Single crystal toroidal diamond anvils for high pressure experiments beyond 5 megabar.

Static compression experiments over 4 Mbar are rare, yet critical for developing accurate fundamental physics and chemistry models, relevant to a range of topics including modeling planetary interiors. Here we show that focused ion beam crafted toroidal single-crystal diamond anvils with ~9.0 µm culets are capable of producing pressures over 5 Mbar. The toroidal surface prevents gasket outflow and provides a means to stabilize the central culet. We have reached a maximum pressure of ~6.15 Mbar using Re as in situ pressure marker, a pressure regime typically accessed only by double-stage diamond anvils and dynamic compression platforms. Optimizing single-crystal diamond anvil design is key for extending the pressure range over which studies can be performed in the diamond anvil cell.

Anomalous elastic properties across the γ to α volume collapse in cerium.

The behavior of the f-electrons in the lanthanides and actinides governs important macroscopic properties but their pressure and temperature dependence is not fully explored. Cerium with nominally just one 4f electron offers a case study with its iso-structural volume collapse from the γ-phase to the α-phase ending in a critical point (p C, V C, T C), unique among the elements, whose mechanism remains controversial. Here, we present longitudinal (c L) and transverse sound speeds (c T) versus pressure from higher than room temperature to T C for the first time. While c L experiences a non-linear dip at the volume collapse, c T shows a step-like change. This produces very peculiar macroscopic properties: the minimum in the bulk modulus becomes more pronounced, the step-like increase of the shear modulus diminishes and the Poisson's ratio becomes negative-meaning that cerium becomes auxetic. At the critical point itself cerium lacks any compressive strength but offers resistance to shear.

Strength and Debye temperature measurements of cerium across the γ → α volume collapse: the lattice contribution.

The longitudinal and transverse sound speeds, cL and cT, of polycrystalline cerium were measured under pressure across the iso-structural γ-α phase transition at 0.75 GPa to beyond 3 GPa. In contrast to previous methods all quantities were directly obtained and no assumptions were made about the size of the volume collapse. Up to the transition our values for cL are in excellent agreement with previous ones, while our values for cT are significantly lower. We deduce values for the adiabatic bulk modulus BS, the shear modulus [Formula: see text], and the pressure dependent Debye temperature, ΘD(p). ΘD(p) is in good agreement with recent results derived from phonon dispersion measurements on single crystals. The ratio of the Debye temperature values bracketing the transition indicates a lattice contribution to the entropy change across the volume collapse, ΔSvib(γ â†’ α) ≈ (0.68 ± 0.06)kB, consistent with previous results obtained by neutron scattering, but significantly larger than other previously determined values.

X-ray emission spectroscopy of cerium across the γ-α volume collapse transition.

High-pressure x-ray emission measurements are used to provide crucial evidence in the longstanding debate over the nature of the isostructural (α, γ) volume collapse in elemental cerium. Extended local atomic model calculations show that the satellite of the Lγ emission line offers direct access to the total angular momentum observable (J(2)). This satellite experiences a 30% steplike decrease across the volume collapse, validating the Kondo model in conjunction with previous measurements. Direct comparisons are made with previous predictions by dynamical mean field theory. A general experimental methodology is demonstrated for analogous work on a wide range of strongly correlated f-electron systems.

Thermal signatures of the Kondo volume collapse in cerium.

X-ray diffraction measurements of cerium in the vicinity of the isostructural gamma-alpha transition have been performed with high precision and accuracy from room temperature to almost 800 K. The disputed location of the critical point has been found to occur at 1.5+/-0.1 GPa and 480+/-10 K. The data are well fit by the Kondo volume collapse model plus a quasiharmonic representation of the phonons. The resultant free energy is validated against data for the thermodynamic Grüneisen parameter and, beyond the dominant spin-fluctuation contribution, indicates a dramatic change in the lattice Grüneisen parameter across the transition.

Martensitic fcc-to-hcp transformation observed in xenon at high pressure.

Angle-resolved x-ray diffraction patterns of Xe to 127 GPa indicate that the fcc-to-hcp transition occurs martensitically between 3 and 70 GPa in diamond-anvil cells without an intermediate phase. These data also reveal that the transition occurs by the introduction of stacking disorder in the fcc lattice at low pressure, which grows into hcp domains with increasing pressure. The small energy difference between the hcp and the fcc structures may allow the two phases to coexist over a wide pressure range. Evidence of similar stacking disorder and incipient growth of an hcp phase are also observed in solid Kr.

Nonlinear carbon dioxide at high pressures and temperatures.

A nonlinear molecular carbon dioxide phase IV was discovered by laser heating CO2-III (Cmca) between 12 and 30 GPa, followed by quenching to 300 K. The Raman spectrum of quenched CO2-IV exhibits a triplet bending mode nu2(O = C = O) near 650 cm (-1), suggesting a broken inversion symmetry because of bending. The 650 cm (-1) bending modes soften with increasing pressure, indicating an enhanced intermolecular interaction among neighboring bent CO2 molecules. At 80 GPa, the low-frequency vibron collapses into high-frequency phonons, and CO2-IV becomes an extended amorphous solid.

New beta(fcc)-cobalt to 210 GPa

We report a new phase transition in cobalt from the magnetic varepsilon(hcp) to a beta(fcc) phase, likely nonmagnetic, at 105 GPa. It occurs martensitically in an extended pressure region between 105 and 150 GPa without any apparent volume change. The fcc phase of Co is in systematic accordance with the 4d and 5d counterparts. The pressure-volume isotherm of beta-Co resembles those of alpha(fcc)-Ni and varepsilon(hcp)-Fe within 1%. The phase diagram of cobalt suggests that the fcc stability increases with increasing occupancy of d-band electrons from Fe to Co to Ni.

Quartzlike carbon dioxide: An optically nonlinear extended solid at high pressures and temperatures

An extended-solid phase, carbon dioxide phase V (CO2-V), was synthesized in a diamond anvil cell by laser heating the molecular orthorhombic phase, carbon dioxide phase III, above 40 gigapascals and 1800 kelvin. This new material can be quenched to ambient temperature above 1 gigapascal. The vibration spectrum of CO2-V is similar to that of the quartz polymorph of silicon dioxide, indicating that it is an extended covalent solid with carbon-oxygen single bonds. This material is also optically nonlinear, generating the second harmonic of a neodymium-yttrium-lithium-fluoride laser at a wavelength of 527 nanometers with a conversion efficiency that is near 0.1 percent.