The Matter at Extremes Group (MEx) was created in July 2015 and composed of beamlines originating from the previous Dynamics and Extreme Conditions (DEC) and Electronic Structure and Magnetism (ESM) groups. Most of the beamlines are either devoted to studies of matter at extreme conditions of pressure and temperature (ID27 and the new ID15B are both fully dedicated to high pressure XRD), or run an important extreme conditions programme in parallel to other fields of research (ID18 - Nuclear Resonance, ID06 - Large Volume Press and Hard X-ray Microscope, ID24 - Energy Dispersive XAS and BM23 – EXAFS).

This chapter reflects the diversity of the science areas covered by the beamlines of the MEx group and also reports related research from the CRG beamlines BM30B and BM26A.

A major milestone of 2015 was the closure of the Phase I upgrade projects. UPBL11, completed in 2012, involved the upgrade of ID24 and the transfer and mild upgrade of BM29 to BM23. The performance of ID24 was boosted by an increase in acquisition speed of two orders of magnitude (readout time decreased from ~ 200 to 2 microseconds). The quality of EXAFS data acquired with a single (100 ps) X-ray bunch at the upgraded beamline witnessed a leap in quality, opening the way to new experiments to probe matter at the extremes of thermodynamic states (pressure, temperature, magnetic field) that can only be maintained for a very short time. New facilities for users include a micro-XAS station (BM23), an “in situ” laser heating facility for the diamond anvil cell (ID24), and a new IR spectrometer for synchronous XAS/DRIFTS structure-function studies of catalysts (ID24 and BM23). New reference papers for both beamlines appeared recently (BM23: O. Mathon et al., JSR 2015, ID24: S. Pascarelli et al., JSR 2016).

After 21 years of faithful and very productive operation, ID09A was closed in November 2015. The beamline will be upgraded and transferred to ID15B. As these highlights go into press, the hutch complex and its infrastructure are finished on schedule, and newly-designed optical components are being delivered. The new beamline will accept proposals for the upcoming round and user operation at ID15B should start after the summer shutdown. Unfortunately, only a small fraction of the exciting results published this year from work at ID09A made it into this chapter, and I would like to mention two that were left out. The first concerns a detailed and accurate single crystal XRD structural study of CrOCl in a diamond anvil cell (M. Bykhov, Sci. Rep. 2015). Contrary to the expectation that materials should approach high symmetry close-packed structures on increasing pressure, a number of elements possess extraordinary complex incommensurately modulated or self-hosting composite structures at high pressures. The significance of this work lies in showing for the first time this incommensurability as an intrinsic high-pressure effect. The second is devoted to a detailed study of the crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesised at pressures and temperatures corresponding to the top of the Earth’s D’’ layer (135 GPa and 2650 K) (M. Merlini, American Mineralogist 2015). These structures suggest that the mineralogy of the lower mantle and D’’ region may be more complex than previously estimated.

The Hard X-ray Microscope (HXRM) project at ID06, a collaboration between the Technical University of Denmark (DTU), Norwegian University of Science and Technology (NTNU) and Utrecht University, is entering its final installation phase and commissioning with beam is planned for the autumn of 2016. This microscope will enable 3D mapping of orientation and stresses down to 100 nm in spatial resolution. Proof of concept experiments (H. Simons et al., Nat. Commun 2015; see chapter Enabling Technologies) have continued with first experiments on multiferroics and 3D dislocation networks. Si refractive lens are now routinely used as condenser for line beams in HXRM experiments, with a first paper already published (H. Simons et al. Optics Communications 2016). This year, much time was devoted to the characterisation of Be and Al refractive lenses using grating interferometry (F. Koch et al. Proc. of SPIE 2015).

The large volume press (LVP) at ID06 has continued operation at 30% of the standard allocation time throughout 2015. The most significant results this year were related to studies of deformation under high pressure high temperature conditions (HP-HT), typically in the field of earth sciences. The main goal is to quantify rheological materials and to understand the deformation mechanisms of relevant minerals in order to build flow-laws at HP-HT that can be used in global geodynamic modelling. A first paper describing the HP-HT deformation apparatus has been published (J. Guignard, Rev. Sci. Instr. 2015), and provides examples of strain and stress measurements, stress partitioning, simple shear and texture analysis. Due to an increasing user demand for the LVP and to the reorganisation of the activities at ID06, starting from spring 2016, the beamtime for the LVP user programme has been increased to 40-50% which will allow increased user access and boost the visibility of this instrument. The deformation projects will be extended in 2016 towards high strain (>30%) and transition zone pressures.

The Nuclear Resonance Beamline, ID18, had a very busy year 2015. A review of its medium term scientific plans took place in November, linked to a discussion on further developments of the beamline within ESRF-EBS. In parallel to the preparation of this important event, several exciting articles were published. Although not included here, a surface science study by nuclear inelastic scattering (NIS) stands out. It deals with the investigation of phonons in ultrathin oxide films, and discusses the 2D to 3D transition in FeO on Pt(111) (N. Spiridis, Phys. Rev. Lett. 2015). This work addressed a long standing general quest in vibrational spectroscopy, and could be achieved due to special preparation of the sample and the nuclear resonance techniques.

Finally, the year 2015 has seen the usual dearth of high impact papers from the high pressure beamline ID27. Among the benchmarks, I would like to mention the first paper exploiting the new Soller slit system for collection of high quality XRD patterns at HP-HT on liquids (G. Weck, PRB 2015). Here, accurate measurements of the liquid hydrogen structure factor to 5 GPa show evidence of a crossover between two density evolutions. Another article worth mentioning deals with high pressure studies of nitrogen-hydrogen compounds (H. Wang, Sci. Rep. 2015) that appear particularly appealing as high energy density materials (HEDM), i.e. materials that release a large amount of energy at their, possibly explosive, decomposition to the most stable species. Results from these investigations open a way for the practical synthesis of these extremely high energetic materials as the formation of nitrogen-hydrogen compounds is favourable already at pressures above 2 GPa according to calculations.

S. Pascarelli