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Abstract Carbon nitrides featuring three‐dimensional frameworks of CN₄tetrahedra are one of the great aspirations of materials science, expected to have a hardness greater than or comparable to diamond. After more than three decades of efforts to synthesize them, no unambiguous evidence of their existence has been delivered. Here, the high‐pressure high‐temperature synthesis of three carbon–nitrogen compounds,tI14‐C₃N₄,hP126‐C₃N₄, andtI24‐CN₂, in laser‐heated diamond anvil cells, is reported. Their structures are solved and refined using synchrotron single‐crystal X‐ray diffraction. Physical properties investigations show that these strongly covalently bonded materials, ultra‐incompressible and superhard, also possess high energy density, piezoelectric, and photoluminescence properties. The novel carbonmore » nitrides are unique among high‐pressure materials, as being produced above 100 GPa they are recoverable in air at ambient conditions.« less

Abstract Transition metal nitrides, particularly those of 5 d metals, are known for their outstanding properties, often relevant for industrial applications. Among these metal elements, tungsten is especially attractive given its low cost. In this high‐pressure investigation of the W–N system, two novel ultra‐incompressible tungsten nitride superconductors, namely W ₂ N ₃ and W ₃ N ₅ , are successfully synthesized at 35 and 56 GPa, respectively, through a direct reaction between N ₂ and W in laser‐heated diamond anvil cells. Their crystal structure is determined using synchrotron single‐crystal X‐ray diffraction. While the W ₂ N ₃ solid's sole constituting nitrogenmore » species are N ^3‐ units, W ₃ N ₅ features both discrete N ^3‐ as well as N ₂ ^4‐ pernitride anions. The bulk modulus of W ₂ N ₃ and W ₃ N ₅ is experimentally determined to be 380(3) and 406(7) GPa, and their ultra‐incompressible behavior is rationalized by their constituting WN ₇ polyhedra and their linkages. Importantly, both W ₂ N ₃ and W ₃ N ₅ are recoverable to ambient conditions and stable in air. Density functional theory calculations reveal W ₂ N ₃ and W ₃ N ₅ to have a Vickers hardness of 30 and 34 GPa, and superconducting transition temperatures at ambient pressure (50 GPa) of 11.6 K (9.8 K) and 9.4 K (7.2 K), respectively. Additionally, transport measurements performed at 50 GPa on W ₂ N ₃ corroborate with the calculations.« less

Recent advances in methods to access nitride systems by a high-pressure high-temperature approach have made possible the one-step synthesis of mixed ternary non-metal nitrides. As a prerequisite to use in a practical device, it is important to understand important bulk electronic properties, such as the band gap, as well as characterizing the presence and effect of defects that are present. In this work, the novel ternary nitride BP₃N₆ is studied using techniques sensitive to the partial electronic density of states, specifically X-ray absorption spectroscopy and X-ray emission spectroscopy. Complementary full-potential all-electron density functional theory (DFT) calculations allow important bulk electronicmore » parameters, such as the band gap, to be elucidated. The band gap of BP₃N₆ has been determined to be 3.9 ± 0.2 eV and 4.1 ± 0.4 eV at the B K- and N K-edges, respectively. This is close to a theoretical value of 4.3 eV predicted by the PBEsol exchange–correlation functional and considerably less than a value of 5.8 eV predicted by the modified Becke–Johnson exchange–correlation functional. X-Ray excited optical luminescence (XEOL) measurements are performed to interrogate the presence of point defects in this system. Together with DFT calculations, these measurements reveal the presence of nitrogen vacancies which lead to multiple mid-gap trap states.« less

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K₀ = 28(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re₂(N₂)(N)₂. Unlike known transition metals pernitrides Re₂(N₂)(N)₂ contains both pernitride N₂^4– and discrete N^3– anions, which explains its exceptional properties. Re₂(N₂)(N)₂ can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambientmore » conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH₄N₃, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re₂(N₂)(N)₂ turned to be at a threshold for superhard materials.« less