Search

Carbon nitrides featuring three-dimensional frameworks of CN4 tetrahedra 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, and tI24-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 carbon nitrides are unique among high-pressure materials, as being produced above 100 GPa they are recoverable in air at ambient conditions., Funding: National Science Foundation - Earth Sciences; DOE Office of Science; Deutsche Forschungsgemeinschaft (DFG) [EAR - 1634415]; UKRI Future Leaders Fellowship [DE-AC02-06CH11357]; DFG [LA-4916/1-1, DU 945/15-1, DU 393-9/2, DU 393-13/1, MR/V025724/1]; DFG [DU 954-11/1]; BIOVIA [INST 91/315-1 FUGG, INST 91/251-1 FUGG]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University; Swedish Research Council (VR); Knut and Alice Wallenberg Foundation [2009 00971]; Swedish Research Council [2019-05600]; RSF [KAW-2018.0194]; [2022-06725]; [2018-05973]; [22-12-00193]

The yttrium-hydrogen system has gained attention because of near-ambient temperature superconductivity reports in yttrium hydrides at high pressures. We conducted a study using synchrotron single-crystal x-ray diffraction (SCXRD) at 87 to 171 GPa, resulting in the discovery of known (two YH3 phases) and five previously unknown yttrium hydrides. These were synthesized in diamond anvil cells by laser heating yttrium with hydrogen-rich precursors-ammonia borane or paraffin oil. The arrangements of yttrium atoms in the crystal structures of new phases were determined on the basis of SCXRD, and the hydrogen content estimations based on empirical relations and ab initio calculations revealed the following compounds: Y3H11, Y2H9, Y4H23, Y13H75, and Y4H25. The study also uncovered a carbide (YC2) and two yttrium allotropes. Complex phase diversity, variable hydrogen content in yttrium hydrides, and their metallic nature, as revealed by ab initio calculations, underline the challenges in identifying superconducting phases and understanding electronic transitions in high-pressure synthesized materials., Funding Agencies|Deutsche Forschungsgemeinschaft (DFG) [BY112/2-1, DU 954-11/1, DU 393-9/2, DU 393-13/1, DU 945/15- 1]; UKRI Future Leaders Fellowship [MR/V025724/1]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoeping University [2009 00971]; NSF-earth Sciences [EAR-1634415]; DOE Office of Science [DE-AC02- 06CH11357]; Open Access Publishing Fund of the University of Bayreuth

Transition metal nitrides, particularly those of 5d 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 W2N3 and W3N5, are successfully synthesized at 35 and 56 GPa, respectively, through a direct reaction between N2 and W in laser-heated diamond anvil cells. Their crystal structure is determined using synchrotron single-crystal X-ray diffraction. While the W2N3 solid's sole constituting nitrogen species are N3- units, W3N5 features both discrete N3- as well as N24- pernitride anions. The bulk modulus of W2N3 and W3N5 is experimentally determined to be 380(3) and 406(7) GPa, and their ultra-incompressible behavior is rationalized by their constituting WN7 polyhedra and their linkages. Importantly, both W2N3 and W3N5 are recoverable to ambient conditions and stable in air. Density functional theory calculations reveal W2N3 and W3N5 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 W2N3 corroborate with the calculations. Two recoverable tungsten nitrides, namely W2N3 and W3N5, are synthesized using laser-heated diamond anvil cells. Both compounds exhibit a high bulk modulus, hardness, and superconducting transition temperature. image, Funding Agencies|UKRI Future Leaders Fellowship; European Synchrotron Radiation Facility (ESRF) [ID15B]; Deutsche Forschungsgemeinschaft [DFG Emmy-Noether, BY112/2-1]; Friedrich Naumann Foundation for Freedom; Federal Ministry of Education and Research (BMBF); European Research Council (ERC) under the European Union [101002868]; National Science Foundation [EAR-1634415]; DOE Office of Science by Argonne National Laboratory [DE-AC02-06CH11357]; Knut and Alice Wallenberg Foundation (Wallenberg Scholar grant) [KAW-2018.0194, Mrc-Mr/T043733/1]; Guangdong Basic and Applied Basic Research Foundation [2022a1515110404]; Swedish Research Council [2022-06725, 2018-05973]; [MR/V025724/1]

The field of polyhalogen chemistry, specifically polyhalogenanions(polyhalides), is rapidly evolving. Here, we present the synthesisof three sodium halides with unpredicted chemical compositions andstructures (tP10-Na2Cl3, hP18-Na4Cl5, and hP18-Na4Br5), a series of isostructural cubic cP8-AX(3) halides (NaCl3, KCl3, NaBr3, and KBr3), and a trigonal potassiumchloride (hP24-KCl3). The high-pressuresyntheses were realized at 41-80 GPa in diamond anvil cellslaser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction(XRD) provided the first accurate structural data for the symmetrictrichloride Cl-3 (-) anion in hP24-KCl3 and revealed the existence of two different typesof infinite linear polyhalogen chains, [Cl]( infinity ) ( n-) and [Br]( infinity ) ( n-), in the structures of cP8-AX(3) compounds and in hP18-Na4Cl5 and hP18-Na4Br5. In Na4Cl5 and Na4Br5, we found unusually short, likely pressure-stabilized, contactsbetween sodium cations. Ab initio calculations support the analysisof structures, bonding, and properties of the studied halogenides., Funding Agencies|China Scholarship Council (CSC); 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 [MR/V025724/1]; UKRI Future Leaders Fellowship [2019-05600]; Knut and Alice Wallenberg Foundation (Wallenberg Scholar grant) [2022-06725]; Swedish Research Council (VR) [BY112/2-1]; Swedish Research Council

A series of isostructural Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) oxoguanidinates was synthesized under high-pressure (25-54 GPa) high-temperature (2000-3000 K) conditions in laser-heated diamond anvil cells. The crystal structure of this novel class of compounds was determined via synchrotron single-crystal X-ray diffraction (SCXRD) as well as corroborated by X-ray absorption near edge structure (XANES) measurements and density functional theory (DFT) calculations. The Ln(3)O(2)(CN3) solids are composed of the hitherto unknown CN35- guanidinate anion-deprotonated guanidine. Changes in unit cell volumes and compressibility of Ln(3)O(2)(CN3) (Ln=La, Eu, Gd, Tb, Ho, Yb) compounds are found to be dictated by the lanthanide contraction phenomenon. Decompression experiments show that Ln(3)O(2)(CN3) compounds are recoverable to ambient conditions. The stabilization of the CN35- guanidinate anion at ambient conditions provides new opportunities in inorganic and organic synthetic chemistry., Funding Agencies|National Science Foundation; DOE Office of Science by Argonne National Laboratory; UKRI Future Leaders Fellowship; Deutsche Forschungsgemeinschaft (DFG) [DE-AC02-06CH11357, MR/V025724/1, 2009 00971]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University; Projekt DEAL; [DU 954-11/1]; [DU 393-9/2]; [DU 393-13/1]; [DU 945/15-1]; [EAR- 1634415]

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]

A high-pressure (HP) yttrium allotrope, hP3-Y (space group P6/mmm), was synthesized in a multi-anvil press at 20 GPa and 2000 K which is recoverable to ambient conditions. Its relative stability and electronic properties were investigated using density functional theory calculations. A hP3-Y derivative hydride, hP3-YHx, with a variable hydrogen content (x = 2.8, 3, 2.4), was synthesized in diamond anvil cells by the direct reaction of yttrium with paraffin oil, hydrogen gas, and ammonia borane upon laser heating to similar to 3000 K at 51, 45 and 38 GPa, respectively. Room-temperature decompression leads to gradual reduction and eventually the complete loss of hydrogen at ambient conditions. Isostructural hP3-NdHx and hP3-GdHx hydrides were synthesized from Nd and Gd metals and paraffin oil, suggesting that the hP3-Y structure type may be common for rare-earth elements. Our results expand the list of allotropes of trivalent lanthanides and their hydrides and suggest that they should be considered in the context of studies of HP behavior and properties of this broad class of materials., Funding Agencies|UKRI Future Leaders Fellowship [MR/V025724/1]; Federal Ministry of Education and Research, Germany [05K19WC1]; Deutsche Forschungsgemeinschaft (DFG) [STE1105/13-2]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [DU 954-11/1]; DFG [DU 393-9/2, DU 393-13/1]; [2009 00971]