Synthesis and Stability of High-Energy-Density Niobium Nitrides under High-Pressure Conditions.

High-energy-density materials (HEDMs) are crucial in various applications, from energy storage to defense technologies. Transition metal polynitrides are promising candidates for HEDMs. Using single-crystal synchrotron X-ray diffraction, we investigated the crystal structures of niobium nitride, specifically NbN and NbN, under high-pressure conditions of up to 86 GPa.

Single crystal diffraction study of Ba[HCO][HCO][HCO][HCO], a hydrous mixed sp/sp-carbonate.

We have synthesized the first hydrous sp-carbonate by laser-heating Ba[CO], CO and HO in a diamond anvil cell at 40(3) GPa. The crystal structure of Ba[HCO][HCO][HCO][HCO] was determined by synchrotron single crystal X-ray diffraction. The experiments were complemented by DFT-based calculations.

High-Pressure Synthesis of an Iron Carbonate, Fe[CO].

We synthesized an iron carbonate, Fe[CO], by reacting FeO with CO at high temperatures and pressures of approximately 33(3) GPa. The structure was solved by single-crystal X-ray diffraction. Full geometry optimizations based on density functional theory reproduced the crystal structure.

6-Fold-Coordinated Beryllium in Calcite-Type Be[CO].

The anhydrous beryllium carbonate Be[CO] with calcite-type crystal structure was obtained by a reaction of BeO with CO in a laser-heated diamond anvil cell at pressures between 30 GPa and 80 GPa and elevated temperatures. Its calcite-type crystal structure (3̅ with = 6) is characterized by 6-fold-coordinated beryllium atoms forming [BeO] octahedra and by trigonal-planar [CO] groups. The crystal structure was determined by synchrotron-based single-crystal X-ray diffraction and confirmed by density-functional-theory-based calculations in combination with experimental Raman spectroscopy.

Polymorphism of pyrene on compression to 35 GPa in a diamond anvil cell.

Structural studies of pyrene have been limited to below 2 GPa. Here, we report on investigations of pyrene up to ~35 GPa using in situ single-crystal synchrotron X-ray diffraction in diamond anvil cells and ab initio calculations. They reveal the phase transitions from pyrene-I to pyrene-II (0.