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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.

In the present-day conditions under which the nuclear power industry is developed, a need arises to diversify the designs of new nuclear power plant units, which should differ from the previously constructed ones by featuring flexibility to the customer requirements and by using safety systems based on fully passive safety assurance principles. In 2022, specialists of Experimental and Design Organization (OKB) Gidropress commenced activities on elaborating the draft design of a new integral pressurized water-cooled reactor plant VVER-I with natural circulation of coolant for a basic thermal capacity of 250 MW. The design incorporates passive safety systems able to provide reliable heat removal from the core under the conditions of a long-term NPP blackout and without the operator's participation. The article presents the results obtained from thermal and fluid dynamic computations of the new reactor plant carried out using the KORSAR/GP code that has been certified for safety analyses. A reactor plant thermal-hydraulic model, which can be used for computations of stationary normal operation conditions and, subsequently, also for simulating the accident scenarios evolvement dynamics, has been developed and tested. Computations carried out using the system code have confirmed a correct choice of the reactor's main geometric parameters and the steam generator's heat-transfer surface for operation at the nominal power. Based on the computation results for optimizing the design, it is proposed to use a jacketed steam generator, which will make it possible to exclude stray coolant leaks in bypass of the heat-transfer surface. It is shown that the newly developed reactor plant has a significant potential for increasing the thermal power capacity up to 400 MW without introducing fundamental changes in the design. The study results can be used in designing new VVER reactors with natural coolant circulation, and also in the development of passive safety systems. [ABSTRACT FROM AUTHOR]

A new cationic palladium complex [Pd(η5-C5H5)(PPh2Cy)2]BF4 (I) is prepared by the reaction of [Pd(acac)(PCyPh2)2]BF4 with cyclopentadiene in the presence of BF3·OEt2. The structure of complex I is determined by XRD. Results of the DFT studies at the BP86-D3/def2-TZVP level of theory along with QTAIM and NOCV methods suggest that the hapticity of the cyclopentadienyl ligand in I adopts an intermediate type of coordination between η3 and η5. Compound I demonstrates a catalytic activity in the reaction of 1,3-butadiene telomerization with methanol with a catalyst turnover number up to 43100 (mol·BD)/(mol·Pd) for 6 h and a 76% selectivity to telomeres. [ABSTRACT FROM AUTHOR]

Subtle anomalies in how the structure of metallic osmium evolves with pressure are detected using powder X-ray diffraction measurements at ultra-high static pressures; the anomaly at 440 gigapascals is attributed to an electronic transition caused by pressure-induced interactions between core electrons. Osmium at extreme pressures The platinum group element osmium is one of the most incompressible of all metals and little is known about its response to extreme compression because the required pressure regime is so difficult to reach. Leonid Dubrovinsky et al. now report powder X-ray diffraction observations of osmium at unprecedentedly high static pressures attained using the state-of-the-art micro-ball nanodiamond anvil cell technique. They detect subtle anomalies in how the structure of the metal evolves at pressures above 770 gigapascals (7.7 megabars). Advanced calculations attribute the anomalies to a type of electronic transition previously unknown for the platinum group and similar metals and caused by pressure-induced interactions between core electrons. The core-level crossing or CLC transition involves pressure-induced interactions between core electrons, leading to observable changes of the material properties. The ability to perform experiments at static pressures that affect the core electrons of even the most incompressible of elements opens up new avenues in the search for new states of matter under extreme conditions. Metallic osmium (Os) is one of the most exceptional elemental materials, having, at ambient pressure, the highest known density and one of the highest cohesive energies and melting temperatures.sup.1. It is also very incompressible.sup.2,3,4, but its high-pressure behaviour is not well understood because it has been studied.sup.2,3,4,5,6 so far only at pressures below 75 gigapascals. Here we report powder X-ray diffraction measurements on Os at multi-megabar pressures using both conventional and double-stage diamond anvil cells.sup.7, with accurate pressure determination ensured by first obtaining self-consistent equations of state of gold, platinum, and tungsten in static experiments up to 500 gigapascals. These measurements allow us to show that Os retains its hexagonal close-packed structure upon compression to over 770 gigapascals. But although its molar volume monotonically decreases with pressure, the unit cell parameter ratio of Os exhibits anomalies at approximately 150 gigapascals and 440 gigapascals. Dynamical mean-field theory calculations suggest that the former anomaly is a signature of the topological change of the Fermi surface for valence electrons. However, the anomaly at 440 gigapascals might be related to an electronic transition associated with pressure-induced interactions between core electrons. The ability to affect the core electrons under static high-pressure experimental conditions, even for incompressible metals such as Os, opens up opportunities to search for new states of matter under extreme compression., Author(s): L. Dubrovinsky [sup.1] , N. Dubrovinskaia [sup.2] , E. Bykova [sup.1] [sup.2] , M. Bykov [sup.2] , V. Prakapenka [sup.3] , C. Prescher [sup.3] , K. Glazyrin [sup.4] , [...]

Laser heating in a diamond anvil cell (DAC) is a common method for studying material behavior at high-pressure and high-temperature conditions. It has been previously proven that during continuous wave (CW) laser heating of a sample, carbon of the diamond anvils is mobilized, and its diffusion into the sample can lead to undesirable chemical reactions, which, if not detected, may cause misinterpretations of the results of the experiment. Minimizing the heating time with the use of a pulsed laser (PL) is thought to reduce the risk of possible carbon contamination of the sample; however, this has not been proven experimentally. Here, we report the results of our comparative study of the effect of pulsed and continuous wave (CW) laser heating on the mobilization of carbon and its chemical interaction with iron in a diamond anvil cell. Using X-ray absorption near edge structure spectroscopy, Synchrotron Mössbauer Source spectroscopy, and Synchrotron X-ray diffraction, we examined iron samples that were laser heated in DACs in various pressure transmitting media (neon, argon, and potassium chloride). According to our results, the use of the PL heating does not prevent the sample from carbon contamination. A reaction between carbon and iron happens within a few seconds even at moderate temperatures. We found that one analytical technique was generally insufficient to fully characterize the phase composition of the laser-heated samples. [ABSTRACT FROM AUTHOR]