Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions1,2. Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials analysis. Here we report on a methodology developed to enable experiments at static compression in the terapascal regime with laser heating. We apply this method to realize pressures of about 600 and 900 gigapascals in a laser-heated double-stage diamond anvil cell3, producing a rhenium–nitrogen alloy and achieving the synthesis of rhenium nitride Re7N3—which, as our theoretical analysis shows, is only stable under extreme compression. Full chemical and structural characterization of the materials, realized using synchrotron single-crystal X-ray diffraction on microcrystals in situ, demonstrates the capabilities of the methodology to extend high-pressure crystallography to the terapascal regime.
Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. This characteristic relies on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly intriguing. In this study, the phosphorus-nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. δ-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two are ultra-incompressible, having a bulk modulus of K0 = 322 GPa for δ-P3N5 and of K0 = 339 GPa for PN2. Upon decompression below 7 GPa, δ-P3N5 undergoes a transformation into a novel α′-P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of α′-P3N5 underlines that a phase space otherwise inaccessible can be explored through high-pressure formed phases.
We present the first nitridic analogs of micas, namely AESi3P4N10(NH)2 (AE=Mg, Mg0.94Ca0.06, Ca, Sr), which were synthesized under high‐pressure high‐temperature conditions at 1400 °C and 8 GPa from the refractory nitrides P3N5 and Si3N4, the respective alkaline earth amides, implementing NH4F as a mineralizer. The crystal structure was elucidated by single‐crystal diffraction with microfocused synchrotron radiation, energy‐dispersive X‐ray spectroscopic (EDX) mapping with atomic resolution, powder X‐ray diffraction, and solid‐state NMR. The structures consist of typical tetrahedra–octahedra–tetrahedra (T‐O‐T) layers with P occupying T and Si occupying O layers, realizing the rare motif of sixfold coordinated silicon atoms in nitrides. The presence of H, as an imide group forming the SiN4(NH)2 octahedra, is confirmed by SCXRD, MAS‐NMR, and IR spectroscopy. Eu2+‐doped samples show tunable narrow‐band emission from deep blue to cyan (451–492 nm).
We report experiments to determine the effect of radiation damage on the phonon spectra of the most common nuclear fuel, UO2. We have irradiated thin (∼ 300 nm) epitaxial films of UO2 with 2.1 MeV He 2+ ions to 0.15 dpa and a lattice swelling of ∆a/a ∼ 0.6 %, and then used grazingincidence inelastic X-ray scattering to measure the phonon spectrum. We succeeded to observe the acoustic modes, both transverse and longitudinal, across the Brillouin zone. The phonon energies, in both the pristine and irradiated samples, are unchanged from those observed in bulk material. On the other hand, the phonon linewidths (inversely proportional to the phonon lifetimes), show a significant broadening when comparing the pristine and irradiated samples. This effect is shown to increase with phonon energy across the Brillouin zone. The decreases in the phonon lifetimes of the acoustic modes are roughly consistent with a 50% reduction in the thermal conductivity.
Recent high-pressure synthesis of pentazolates and subsequent stabilization of the aromatic [N5 -] anion at atmospheric pressure had an immense impact on nitrogen chemistry. Here, we present the first synthesis of an aromatic hexazine [N6] 4anion realized in high-pressure potassium nitride K9N56 at 46 and 61 GPa. The extremely complex structure of K9N56 was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. This result resolves a long-standing question of the aromatic hexazine stability and the possibility of its synthesis.
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