Synthesis of FeN₄ at 180 GPa and its crystal structure from a submicron-sized grain

Iron tetranitride, FeN4, was synthesized from the elements in a laser-heated diamond anvil cell at 180 (5) GPa and 2700 (200) K. Its crystal structure was determined based on single-crystal X-ray diffraction data collected from a submicron-sized grain at the synchrotron beamline ID11 of ESRF. The compound crystallizes in the triclinic space group P\overline{1}. In the asymmetric unit, the Fe atom occupies an inversion centre (Wyckoff position 1d), while two N atoms occupy general positions (2i). The structure is made up from edge-sharing [FeN6] octahedra forming chains along [100] and being interconnected through N—N bridges. N atoms form catena-poly[tetraz-1-ene-1,4-diyl] anions [–N=N—N—N–]∞2− running along [001]. In comparison with the previously reported structure of FeN4 at 135 GPa [Bykov et al. (2018). Nat. Commun. 9, 2756], the crystal structure of FeN4 at 180 GPa is similar but the structural model is significantly improved in terms of the precision of the bond lengths and angles

High-pressure polymeric nitrogen allotrope with the black phosphorus structure

Studies of polynitrogen phases are of great interest for fundamental science and for the design of novel high energy density materials. Laser heating of pure nitrogen at 140 GPa in a diamond anvil cell led to the synthesis of a polymeric nitrogen allotrope with the black phosphorus structure, bp-N. The structure was identified in situ using synchrotron single-crystal X-ray diffraction and further studied by Raman spectroscopy and density functional theory calculations. The discovery of bp-N brings nitrogen in line with heavier pnictogen elements, resolves incongruities regarding polymeric nitrogen phases and provides insights into polynitrogen arrangements at extreme densities

Clean-limit superconductivity in Im3¯m H3S synthesized from sulfur and hydrogen donor ammonia borane

We present detailed studies of the superconductivity in high-pressure H$_3$S. X-ray diffraction measurements show that cubic Im$\bar{3}$m H3S was synthesized from elemental sulfur and hydrogen donor ammonia borane (NH$_3$BH$_3$). Our electrical transport measurements confirm superconductivity with a transition temperature T$_c$=197K at 153 GPa. From the analysis of both the normal-state resistivity and the slope of the critical field, we conclude that the superconductivity is described by clean-limit behavior. A significant broadening of the resistive transition in finite magnetic field is found, as expected for superconductors. We identify a linear temperature-over-field scaling of the resistance at the superconducting transition which is not described by existing theories

Synthesis, crystal structure and structure-property relations of strontium orthocarbonate, Sr₂CO₄

Carbonates containing CO4 groups as building blocks have recently been discovered. A new orthocarbonate, Sr2CO4 is synthesized at 92 GPa and at a temperature of 2500 K. Its crystal structure was determined by in situ synchrotron single-crystal X-ray diffraction, selecting a grain from a polycrystalline sample. Strontium orthocarbonate crystallizes in the orthorhombic crystal system (space group Pnma) with CO4, SrO9 and SrO11 polyhedra as the main building blocks. It is isostructural to Ca2CO4. DFT calculations reproduce the experimental findings very well and have, therefore, been used to predict the equation of state, Raman and IR spectra, and to assist in the discussion of bonding in this compound.Funding Agencies|Alexander von Humboldt-StiftungAlexander von Humboldt Foundation; Bundesministerium fur Bildung und ForschungFederal Ministry of Education &amp; Research (BMBF) [05K19WC1]; Deutsche ForschungsgemeinschaftGerman Research Foundation (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1, FOR2125, WI1232]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [2009 00971]</p

High-pressure synthesis of dysprosium carbides

Chemical reactions between dysprosium and carbon were studied in laser-heated diamond anvil cells at pressures of 19, 55, and 58 GPa and temperatures of similar to 2500 K. In situ single-crystal synchrotron X-ray diffraction analysis of the reaction products revealed the formation of novel dysprosium carbides, Dy4C3 and Dy3C2, and dysprosium sesquicarbide Dy2C3 previously known only at ambient conditions. The structure of Dy4C3 was found to be closely related to that of dysprosium sesquicarbide Dy2C3 with the Pu2C3-type structure. Ab initio calculations reproduce well crystal structures of all synthesized phases and predict their compressional behavior in agreement with our experimental data. Our work gives evidence that high-pressure synthesis conditions enrich the chemistry of rare earth metal carbides.Funding Agencies|Federal Ministry of Education and Research, Germany (BMBF) [05K19WC1]; Deutsche Forschungsgemeinschaft (DFG) [DU 954-11/1, DU 393-9/2, DU 393-13/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; UKRI Future Leaders Fellowship [MR/V025724/1]</p

Thermal Equation of State of Cubic Silicon Carbide at High Pressures

We have performed in situ X-ray diffraction measurements of cubic silicon carbide (SiC) with a zinc-blende crystal structure (B3) at high pressures and temperatures using multi-anvil apparatus. The ambient volume inferred from the compression curves is smaller than that of the starting material. Using the 3$^{rd}$-order Birch-Murnaghan equation of state and the Mie-Grüneisen-Debye model, we have determined the thermoelastic parameters of the B3-SiC to be K$_0$=228±3 GPa, K$_0$’,=4.4±0.4, q=0.27±0.37, where K$_0$, K$_0$’ and q are the isothermal bulk modulus, its pressure derivative and logarithmic volume dependence of the Grüneisen parameter, respectively. Using the 3rd-order Birch-Murnaghan EOS with the thermal expansion coefficient, the thermoelastic parameters have been found as K$_0$=221±3 GPa, K$_0$’,=5.2±0.4, α$_0$=0.90±0.02 ⋅ 10$^{−5}$ ⋅ K$^{−1}$, where α$_0$ is the thermal expansion coefficient at room pressure and temperature. We have determined that paired B3-SiC – MgO calibrants can be used to estimate pressure and temperature simultaneously in ultrahigh-pressure experiments up to 60 GPa

Anionic N₁₈ Macrocycles and a Polynitrogen Double Helix in Novel Yttrium Polynitrides YN₆ and Y₂N₁₁ at 100 GPa

Two novel yttrium nitrides, YN(6) and Y(2)N(11), were synthesized by direct reaction between yttrium and nitrogen at 100 GPa and 3000 K in a laser‐heated diamond anvil cell. High‐pressure synchrotron single‐crystal X‐ray diffraction revealed that the crystal structures of YN(6) and Y(2)N(11) feature a unique organization of nitrogen atoms—a previously unknown anionic N(18) macrocycle and a polynitrogen double helix, respectively. Density functional theory calculations, confirming the dynamical stability of the YN(6) and Y(2)N(11) compounds, show an anion‐driven metallicity, explaining the unusual bond orders in the polynitrogen units. As the charge state of the polynitrogen double helix in Y(2)N(11) is different from that previously found in Hf(2)N(11) and because N(18) macrocycles have never been predicted or observed, their discovery significantly extends the chemistry of polynitrides