Phase transition kinetics of superionic HO ice phases revealed by Megahertz X-ray free-electron laser-heating experiments.

HO transforms to two forms of superionic (SI) ice at high pressures and temperatures, which contain highly mobile protons within a solid oxygen sublattice. Yet the stability field of both phases remains debated. Here, we present the results of an ultrafast X-ray heating study utilizing MHz pulse trains produced by the European X-ray Free Electron Laser to create high temperature states of HO, which were probed using X-ray diffraction during dynamic cooling.

Crystal chemistry and compressibility of FeMgAlSiO and FeMgSiO silicate perovskites at pressures up to 95 GPa.

Silicate perovskite, with the mineral name bridgmanite, is the most abundant mineral in the Earth's lower mantle. We investigated crystal structures and equations of state of two perovskite-type Fe-rich phases, FeMgSiO and FeMgAlSiO, at high pressures, employing single-crystal X-ray diffraction and synchrotron Mössbauer spectroscopy. We solved their crystal structures at high pressures and found that the FeMgSiO phase adopts a novel monoclinic double-perovskite structure with the space group of at pressures above 12 GPa, whereas the FeMgAlSiO phase adopts an orthorhombic perovskite structure with the space group of at pressures above 8 GPa.

Reducibility of Al-Modified CoO: Influence of Aluminum Distribution.

The reduction of Co-based oxides doped with Al ions has been studied using in situ XRD and TPR techniques. Al-modified CoO oxides with the Al mole fraction Al/(Co + Al) = 1/6; 1/7.5 were prepared via coprecipitation, with further calcination at 500 and 850 °C.

A MHz X-ray diffraction set-up for dynamic compression experiments in the diamond anvil cell.

An experimental platform for dynamic diamond anvil cell (dDAC) research has been developed at the High Energy Density (HED) Instrument at the European X-ray Free Electron Laser (European XFEL). Advantage was taken of the high repetition rate of the European XFEL (up to 4.5 MHz) to collect pulse-resolved MHz X-ray diffraction data from samples as they are dynamically compressed at intermediate strain rates (≤10 s), where up to 352 diffraction images can be collected from a single pulse train.

Revealing the Complex Nature of Bonding in the Binary High-Pressure Compound FeO_{2}.

Extreme pressures and temperatures are known to drastically affect the chemistry of iron oxides, resulting in numerous compounds forming homologous series nFeOmFe_{2}O_{3} and the appearance of FeO_{2}. Here, based on the results of in situ single-crystal x-ray diffraction, Mössbauer spectroscopy, x-ray absorption spectroscopy, and density-functional theory+dynamical mean-field theory calculations, we demonstrate that iron in high-pressure cubic FeO_{2} and isostructural FeO_{2}H_{0.5} is ferric (Fe^{3+}), and oxygen has a formal valence less than 2.

Nitro-sonium nitrate (NONO ) structure solution using single-crystal X-ray diffraction in a diamond anvil cell.

At high pressures, autoionization - along with polymerization and metallization - is one of the responses of simple molecular systems to a rise in electron density. Nitro-sonium nitrate (NONO ), known for this property, has attracted a large interest in recent decades and was reported to be synthesized at high pressure and high temperature from a variety of nitro-gen-oxygen precursors, such as NO, NO and N-O mixtures. However, its structure has not been determined unambiguously.

Polymorphism of feldspars above 10 GPa.

Feldspars are rock-forming minerals that make up most of the Earth's crust. Along the mantle geotherm, feldspars are stable at pressures up to 3 GPa and may persist metastably at higher pressures under cold conditions. Previous structural studies of feldspars are limited to ~10 GPa, and have shown that the dominant mechanism of pressure-induced deformation is the tilting of AlO and SiO tetrahedra in a tetrahedral framework.

The crystal structures of Fe-bearing MgCO - and -carbonates at 98 GPa from single-crystal X-ray diffraction using synchrotron radiation.

The crystal structure of MgCO-II has long been discussed in the literature where DFT-based model calculations predict a pressure-induced transition of the carbon atom from the to the type of bonding. We have now determined the crystal structure of iron-bearing MgCO-II based on single-crystal X-ray diffraction measurements using synchrotron radiation. We laser-heated a synthetic (MgFe)CO single crystal at 2500 K and 98 GPa and observed the formation of a monoclinic phase with composition (MgFe)CO in the space group 2/ that contains tetra-hedrally coordinated carbon, where CO tetra-hedra are linked by corner-sharing oxygen atoms to form three-membered CO ring anions.

Raman Spectroscopy Study on Chemical Transformations of Propane at High Temperatures and High Pressures.

This study is devoted to the detailed in situ Raman spectroscopy investigation of propane CH in laser-heated diamond anvil cells in the range of pressures from 3 to 22 GPa and temperatures from 900 to 3000 K. We show that propane, while being exposed to particular thermobaric conditions, could react, leading to the formation of hydrocarbons, both saturated and unsaturated as well as soot. Our results suggest that propane could be a precursor of heavy hydrocarbons and will produce more than just sooty material when subjected to extreme conditions.

Synthesis of magnesium-nitrogen salts of polynitrogen anions.

The synthesis of polynitrogen compounds is of fundamental importance due to their potential as environmentally-friendly high energy density materials. Attesting to the intrinsic difficulties related to their formation, only three polynitrogen ions, bulk stabilized as salts, are known. Here, magnesium and molecular nitrogen are compressed to about 50 GPa and laser-heated, producing two chemically simple salts of polynitrogen anions, MgN and MgN.

Boron Phosphorus Nitride at Extremes: PN Octahedra in the High-Pressure Polymorph β-BP N.

The high-pressure behavior of non-metal nitrides is of special interest for inorganic and theoretical chemistry as well as materials science, as these compounds feature intriguing elastic properties. The double nitride α-BP N was investigated by in situ single-crystal X-ray diffraction (XRD) upon cold compression to a maximum pressure of about 42 GPa, and its isothermal bulk modulus at ambient conditions was determined to be 146(6) GPa. At maximum pressure the sample was laser-heated, which resulted in the formation of an unprecedented high-pressure polymorph, β-BP N .

Fe-N system at high pressure reveals a compound featuring polymeric nitrogen chains.

Poly-nitrogen compounds have been considered as potential high energy density materials for a long time due to the large number of energetic N-N or N=N bonds. In most cases high nitrogen content and stability at ambient conditions are mutually exclusive, thereby making the synthesis of such materials challenging. One way to stabilize such compounds is the application of high pressure.

High-Pressure Synthesis of a Nitrogen-Rich Inclusion Compound ReN ⋅x N with Conjugated Polymeric Nitrogen Chains.

A nitrogen-rich compound, ReN ⋅x N , was synthesized by a direct reaction between rhenium and nitrogen at high pressure and high temperature in a laser-heated diamond anvil cell. Single-crystal X-ray diffraction revealed that the crystal structure, which is based on the ReN framework, has rectangular-shaped channels that accommodate nitrogen molecules. Thus, despite a very high synthesis pressure, exceeding 100 GPa, ReN ⋅x N is an inclusion compound.

Portable double-sided pulsed laser heating system for time-resolved geoscience and materials science applications.

A portable double-sided pulsed laser heating system for diamond anvil cells has been developed that is able to stably produce laser pulses as short as a few microseconds with repetition frequencies up to 100 kHz. In situ temperature determination is possible by collecting and fitting the thermal radiation spectrum for a specific wavelength range (particularly, between 650 nm and 850 nm) to the Planck radiation function. Surface temperature information can also be time-resolved by using a gated detector that is synchronized with the laser pulse modulation and space-resolved with the implementation of a multi-point thermal radiation collection technique.