Formation of uranium polyhydrides UH5–9 is predicted using the evolutionary algorithm USPEX and proved by high-pressure synthesis.

Particle size distributions in the range of 0.01–10 µm were measured in urban Shanghai in the summer of 2013 using a Wide‐range Particle Spectrometer (WPS). Size‐segregated aerosol samples were collected concurrently using a Micro‐Orifice Uniform Deposit Impactor (MOUDI), which aided our in‐depth understanding of the new particle formation (NPF) mechanism in the polluted Yangtze River Delta area. During the observations, 16 NPF events occurred at high temperatures (~34.7°C) on clear and sunny days. In the ammonium‐poor PM1.0 (particulate matter less than 1.0 µm), sulfate and ammonium accounted for 92% of the total water‐soluble inorganic species. Six aminiums were detected in these MOUDI samples, among which the group of diethylaminium and trimethylaminium (DEAH+ + TMAH+) was the most abundant. The very high level of aminiums (average concentration up to 86.4 ng m−3 in PM1.8), together with highly acidic aerosols, provided insight into the frequent NPF events. The high mass ratio of total aminiums to NH4+ (>0.2 for PM0.056) further highlighted the important role of amines in promoting NPF. The concentration of DEAH+ + TMAH+ in new particles below 180 nm was strongly correlated with aerosol phase acidity, indicating that acid‐base reactions dominated the aminium formation in NPF events. The unexpected enhancement of DEAH+ + TMAH+ on a nonevent day was attributed to the transportation of an SO2 plume. Our results reveal that the heterogeneous uptake of amines is dominated by the acid‐base reaction mechanism, which can effectively contribute to particle growth in NPF events.

The recent discovery of H 3 S and LaH 10 superconductors with record high superconducting transition temperatures T c at high pressure has fueled the search for room-temperature superconductivity in the compressed superhydrides. Here we introduce a new class of high T c hydrides with a novel structure and unusual properties. We predict the existence of an unprecedented hexagonal HfH 10 , with remarkably high value of T c (around 213-234 K) at 250 GPa. As concerns the novel structure, the H ions in HfH 10 are arranged in clusters to form a planar "pentagraphenelike" sublattice. The layered arrangement of these planar units is entirely different from the covalent sixfold cubic structure in H 3 S and clathratelike structure in LaH 10 . The Hf atom acts as a precompressor and electron donor to the hydrogen sublattice. This pentagraphenelike H 10 structure is also found in ZrH 10 , ScH 10 , and LuH 10 at high pressure, each material showing a high T c ranging from 134 to 220 K. Our study of dense superhydrides with pentagraphenelike layered structures opens the door to the exploration of a new class of high T c superconductors.

The structural studies of lithium amide (LiNH2) have been performed by synchrotron X-ray diffraction measurements and ab initio density functional theoretical calculations up to 28.0 GPa. It is revealed that LiNH2 undergoes a reversible pressure-induced phase transitions from tetragonal phase (I-4) into the monoclinic phase (P21), which starts from about 10.3 GPa and completes at about 15.0 GPa. This transition is accompanied by about 11% large volume collapse, and this volume collapse is much larger than other complex ternary hydrides. The experimental pressure–volume data for the two phases of LiNH2 are fitted by third-order Birch–Murnaghan equation of state, yielding B 0 of 37.2 (1.7) GPa for the tetragonal phase and 7.6 (4.9) GPa for the monoclinic phase with the pressure derivatives at 3.5. We also have calculated the total and partial density of states of the two phases in order to explore the mechanism of the volume reduction.

The chemical reaction products of molecular hydrogen (H 2 ) with selenium (Se) are studied by synchrotron x-ray diffraction (XRD) and Raman spectroscopy at high pressures. We find that a common H 2 Se is synthesized at 0.3 GPa using laser heating.

We studied the phase transition behavior of cubic BaZrO3 perovskite by in situ high pressure synchrotron X-ray diffraction experiments up to 46.4 GPa at room temperature. The phase transition from cubic phase to tetragonal phase was observed in BaZrO3 for the first time, which takes place at 17.2 GPa. A bulk modulus 189 (26) GPa for cubic BaZrO3 is derived from the pressure–volume data. Upon decompression, the high pressure phase transforms into the initial cubic phase. It is suggested that the unstable phonon mode caused by the rotation of oxygen octahedra plays a crucial role in the high pressure phase transition behavior of BaZrO3.

The high-pressure behavior of hydrazine has been investigated by in situ Raman spectroscopy and synchrotron X-ray diffraction experiments under pressure up to 46.5 and 33.0 GPa, respectively. It is found that the liquid hydrazine solidifies into phase I at about 1.2 GPa. The symmetry of phase I is confirmed to be space group P2 1 by the peak assignment, group theory analysis, and Rietveld refinement of XRD patterns. A solid−solid transition from phase I to phase II is observed in both Raman spectroscopy and XRD experiments at about 2.4 GPa, which is ascribed to the formation of new hydrogen bonds between hydrazine molecules. At 18.4 GPa, an isostructural transition from phase II to the final phase III is observed. The pressure-induced adjustment of bifurcated hydrogen bond is first researched and regarded as the origin of the isostructural transition. Above 20.6 GPa, a clear softening behavior occurs in the NH 2 symmetric stretching mode. The coupling of optical vibrations derived from enhancement of the hydrogen bond is proposed as a crucial role in this softening process.

Diatomic nitrogen is an archetypal molecular system known for its exceptional stability and complex behavior at high pressures and temperatures, including rich solid polymorphism, formation of energetic states, and an insulator-to-metal transformation coupled to a change in chemical bonding. However, the thermobaric conditions of the fluid molecular–polymer phase boundary and associated metallization have not been experimentally established. Here, by applying dynamic laser heating of compressed nitrogen and using fast optical spectroscopy to study electronic properties, we observe a transformation from insulating (molecular) to conducting dense fluid nitrogen at temperatures that decrease with pressure and establish that metallization, and presumably fluid polymerization, occurs above 125 GPa at 2500 K. Our observations create a better understanding of the interplay between molecular dissociation, melting, and metallization revealing features that are common in simple molecular systems.