B. Couzinet

Toward fully fledged high-pressure macromolecular crystallography

Pressure allows one to explore the energy landscape and the various conformations of macromolecules. This might be one of the most interesting prospects of combining macromolecular crystallography (MX) with pressure perturbation. This paper presents innovations in high-pressure macromolecular crystallography (HPMX). A new-generation diamond anvil cell extends the technical feasibility of HPMX experiments up to about 2.5 GPa (depending on the sample). Thanks to the large useful aperture (82

Optically monitored high-pressure gas loading apparatus for diamond anvil cells

We describe a high-pressure system built to load rare gases (He, Ar, Ne) in various types of diamond anvil cells, at room temperature. These gases are used as pressure transmitting media to obtain the best hydrostatic compression conditions in high-pressure experiments. Optical windows allow control of the loading process. The loading success rate is close to 100% and the initial pressures in the diamond anvil cell are in between 0.2 and 1 GPa. This system can easily be adapted for loading of various gaseous samples, including gas mixtures, which generally cannot be loaded by cryogenic methods.

High pressure x-ray absorption spectroscopy at lower energy in the dispersive mode: application to Ce and FePO4

X-ray absorption spectroscopy (XAS) using a diamond anvil cell has been extended to lower energies (below 6 keV) thanks to smaller diamond anvils and to a new acquisition set-up on the energy dispersive x-ray absorption beamline of LURE. The valence change of Ce with pressure is followed at the LIII edge of cerium up to 8 GPa together with the bond length variation during the same experiment. The pressure induced coordination change around the Fe atom in FePO4 is determined at the Fe K edge through the pre-edge feature behaviour, the XANES modification and the Fe–O bond length increase.

Ti K Pre‐Edge in SrTiO3 under Pressure: Experiments and Full‐Potential First‐Principles Calculations

Strontium titanate exhibits two phase transitions at 5 GPa and 14 GPa. We use X‐ray absorption Ti K pre‐edge structure as a probe of the local atomic structure of SrTiO3 under pressure. The pre‐edge is characterized by four main features labeled A, B, C1 and C2. Above 5 GPa, the intensity of peak B is decreased while that of the double feature C1‐C2 is increased. By increasing the pressure above 14 GPa, peak A shifts towards lower energy and of peak C1 towards higher energy. While the first phase transformation is known to be a transition from the cubic phase to a tetragonal one, the second phase transformation leads to a crystal structure not yet identified. To analyze these spectral modifications, full‐potential first principles simulations of Ti K pre‐edge are performed. The calculations provide a good agreement with experiments and permits the identification of the four features in terms of orbital hybridization. Trial crystal structures are proposed in order to account for the pre‐edge modifications ...

X-ray absorption spectroscopy on titanate perovskites at the Ti K edge

The Ti K edge X-ray absorption has been measured under high pressure at room temperature for ATiO3 perovskites (A = Ca, Sr, Ba and Pb). The pre-edge features have been used to determine the local distortion around the Ti atom as a function of applied features. The ferroelectric local instability decreases when pressure is increased (PbTiO3) and eventually vanishes at high pressure (BaTiO3). The antiferrodistorsive instability remains unchanged under pressure for CaTiO3 and appears above 5 GPa for SrTiO3. Moreover, it is shown that at room pressure SrTiO3 was locally ferroelectric. A new phase appears for SrTiO3 above 14 GPa with a strong deformation of the oxygen octahedron.

New diamond anvil cell for optical and transport measurements under high magnetic fields up to 60 T

We present here a new diamond anvil cell designed to combine high hydrostatic pressure up to 10 GPa, non-destructive, pulsed magnetic fields up to 60 T and low temperature as low as 2 K. Both optical and transport measurements are now achievable. Magneto-photoluminescence set-up under pressure is described in great detail. We report photoluminescence experiments on oriented ruby single crystals exhibiting direct observation of the intrinsic Zeeman splitting of excited states under pressure.

High Pressure XAS at the Ti K Edge on Titanate Perovskites

X‐ray absorption measurements have been performed on BaTiO3 and SrTiO3 at the Ti K edge under pressure. For BaTiO3, the phase transformation to the cubic phase is observed at 2 GPa. In this structure the Ti atoms remain off centre with respect to the oxygen octahedron up to 10 GPa. Above this pressure the Ti atoms are at the centre of the octahedron. For SrTiO3, a first transformation is observed above 5 GPa with a modification of the pre‐edge features. A second one is observed close to 14 GPa with a complete change of the absorption spectrum.

Magnetism under Pressure with Synchrotron Radiation

The magnetic properties of materials depend strongly on the distance between ions and on the volume available for each magnetic ion. In this article, we introduce a birds eye view of the various possible effects of pressure on the magnetic state and the consequences of these effects on the fundamental understanding of the magnetism in condensed matter and on the physics and chemistry of minerals in the interior of the Earth and planets. We will give basic information about the ex- perimental possibilities offered by synchrotron-radiation-based techniques in order to explore the magnetic state of matter at high pressure, their interest and feasi- bility. Finally, we will present some experimental highlights where x-ray techniques using synchrotron radiation have been successfully applied to show and explain the magnetic state of matter at high density.