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We investigated the metastable phase diagram of an ionic salt aqueous solution, LiCl:6D₂O, at high pressure and low temperature by neutron diffraction measurements and computer simulations. We show that the presence of salt triggers a stepwise transformation, under annealing at high pressure, to a new very high-density amorphous form. The transition occurs abruptly at 120 K and 2 GPa, is reversible, and is characterized by a sizeable enthalpy release. Simulations suggest that the polyamorphic transition is linked to a local structural reorganization of water molecules around the Li ions.

High‐pressure method combining diamond anvil cell with picosecond ultrasonics technique is demonstrated to be a very suitable tool to measure the acoustic properties of iron up to 152 GPa. Such innovative approach allows to measure directly the longitudinal sound velocity under pressure of hundreds of GPa in laboratory, overcoming most of the drawbacks of traditional techniques. The very high accuracy, comparable to piezoacoustics technique, allows to observe the kink in elastic properties at the body‐centered cubic–hexagonal close packed transition and to show with a good confidence that the Birch's law still stands up to 1.5 Mbar and ambient temperature. The linear extrapolation of the measured sound velocities versus densities of hcp iron is out of the preliminary reference Earth model, arguing for alloying effects or anharmonic high‐temperature effects. A comparison between our measurements and shock wave experiments allowed us to quantify temperature corrections at constant pressure in ~−0.35 and ~−0.30 m s−1/K at 100 and 150 GPa, respectively. More in general, the here‐presented technique allows detailed elastic and viscoelastic studies under extreme thermodynamic conditions on a wide variety of systems as liquids, crystalline, or polycrystalline solids, metallic or not, with very broad applications in Earth and planetary science.

The acoustic velocity, refractive index, and equation of state of liquid ammonia dihydrate under high pressure and high temperature J. Chem. Phys. 137, 104504 (2012) Ultrafast acoustics measurements on liquid mercury have been performed at high pressure and temperature in a diamond anvil cell using picosecond acoustic interferometry. We extract the density of mercury from adiabatic sound velocities using a numerical iterative procedure. We also report the pressure and temperature dependence of the thermal expansion, isothermal and adiabatic compressibility, bulk modulus, and pressure derivative of the latter up to 7 GPa and 520 K. We finally show that the sound velocity follows a scaling law as a function of density in the overall measured metallic state.

We report a comprehensive study of the noncentrosymmetric superconductor Mo 3 P. Its bulk superconductivity, with T c = 5.5 K, was characterized via electrical resistivity, magnetization, and heat-capacity measurements, while its microscopic electronic properties were investigated by means of muon-spin rotation/relaxation (µSR) and nuclear magnetic resonance (NMR) techniques. In the normal state, NMR relaxation data indicate an almost ideal metallic behavior, confirmed by band-structure calculations, which suggest a relatively high electron density of states, dominated by the Mo 4d-orbitals. The low-temperature superfluid density, determined via transverse-field µSR and electronic specific heat, suggest a fully-gapped superconducting state in Mo 3 P, with ∆ 0 = 0.83 meV, the same as the BCS gap value in the weak-coupling case, and a zero-temperature magnetic penetration depth λ 0 = 126 nm. The absence of spontaneous magnetic fields below the onset of superconductivity, as determined from zero-field µSR measurements, indicates a preserved time-reversal symmetry in the superconducting state of Mo 3 P and, hence, spin-singlet pairing. Superconductivity and spin-orbit coupling in non-centrosymmetric materials:A review, Rep. Prog. Phys. 80, 036501 (2017).

This paper presents details of instrumental development to extend synchrotron X-ray microtomography techniques to in situ studies under static compression (high pressure), shear stress or the both conditions at simultaneous high temperatures. To achieve this, a new rotating tomography Paris-Edinburgh cell has been developed. This ultra-compact portable device easily and successfully adapted to various multi-modal synchrotron experimental set-up at ESRF, SOLEIL and DIAMOND is explained in detail. An in-depth description of proof of concept first experiments performed on a high resolution imaging beamline is then given, which illustrate the efficiency of the set-up and the data quality that can be obtained. ARTICLE HISTORY

Oxygen is the only elemental molecule which carries an electronic magnetic moment. As a consequence, the different solid phases encountered on cooling show various degrees of magnetic order, and similar behavior is expected under compression. Here we present neutron diffraction data which reveal the magnetic ordering under high pressure in the delta ("orange") phase, i.e., in the range 6-8 GPa and 20-240 K. We show that delta-O2 contains in total three different magnetic structures, all of them being antiferromagnetic and differing in the stacking sequence of O2 sheets along the c axis. This structural diversity can be explained by the quasi-two-dimensional nature of delta-O2 and the strong orientation dependence of the magnetic exchange interaction between O2 molecules. The results show that delta-O2 is a room temperature antiferromagnet.

We report the vibrational spectrum of recovered ice VII measured by inelastic incoherent neutron scattering and compare this to similar data of its fully hydrogen-ordered form, ice VIII, under exactly the same conditions (15 K, 1 bar). The spectra of the two phases have their principal features at similar energies, in both the translational and librational bands, with a substantial disorder-related broadening in ice VII. In particular, we find no evidence for a peak at 49 meV in ice VII which earlier was associated with the possible existence of two kinds of hydrogen bonds. Additional Raman measurements in ice VII and ice VIII show that the O-H stretching frequencies in the two phases are almost identical. Therefore, the presence of split molecular-optic bands in ice phases, including ordinary ice Ih, is likely related to an incomplete description of the phonon dispersion rather than to a fundamentally new feature in the nature of the hydrogen bond.