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

High-Pressure Synthesis of the β−Zn3N2β-Zn_{3}N_{2} Nitride and the α−ZnN4α-ZnN_{4} and β−ZnN4β-ZnN_{4} Polynitrogen Compounds

High-pressure nitrogen chemistry has expanded at a formidable rate over the past decade, unveiling the chemical richness of nitrogen. Here, the $Zn-N$ system is investigated in laser-heated diamond anvil cells by synchrotron powder and single-crystal X-ray diffraction, revealing three hitherto unobserved nitrogen compounds: $β-Zn_{3}N_{2}$, $α-ZnN_{4}$, and $β-ZnN_{4}$, formed at 35.0, 63.5, and 81.7 GPa, respectively. Whereas $β-Zn_3N_2$ contains the $N^{3–}$ nitride, both $ZnN_4$ solids are found to be composed of polyacetylene-like [$N_4$]$_∞$$^{2–}$ chains. Upon the decompression of $β-ZnN_4$ below 72.7 GPa, a first-order displacive phase transition is observed from $β-ZnN_4$ to $α-ZnN_4$. The $α-ZnN_4$ phase is detected down to 11.0 GPa, at lower pressures decomposing into the known $α-Zn_3N_2$ (space group Ia3̅) and $N_2$. The equations of states of $β-ZnN_4$ and $α-ZnN_4$ are also determined, and their bulk moduli are found to be $K_0$ = 126(9) GPa and $K_0$ = 76(12) GPa, respectively. Density functional theory calculations were also performed and provide further insight into the $Zn-N$ system. Moreover, comparing the $Mg-N$ and $Zn-N$ systems underlines the importance of minute chemical differences between metal cations in the resulting synthesized phases

Synthesis of Ilmenite-type εε-Mn2_2O3_3 and Its Properties

In contrast to the corundum-type A$_2$X$_3$ structure, which has only one crystallographic site available for trivalent cations (e.g., in hematite), the closely related ABX$_3$ ilmenite-type structure comprises two different octahedrally coordinated positions that are usually filled with differently charged ions (e.g., in Fe$^{2+}$Ti$^{4+}$O$_3$ ilmenite). Here, we report a synthesis of the first binary ilmenite-type compound fabricated from a simple transition-metal oxide (Mn2O3) at high-pressure high-temperature (HP-HT) conditions. We experimentally established that, at normal conditions, the ilmenite-type Mn$^{2+}$Mn$^{2´2+}$O$_3$ ($ε$-Mn$_2$O$_3$) is an n-type semiconductor with an indirect narrow band gap of E$_g$ = 0.55 eV. Comparative investigations of the electronic properties of $ε$-Mn$_2$O$_3$ and previously discovered quadruple perovskite $ζ$-Mn$_2$O$_3$ phase were performed using X-ray absorption near edge spectroscopy. Magnetic susceptibility measurements reveal an antiferromagnetic ordering in $ε$-Mn$_2$O$_3$ below 210 K. The synthesis of $ε$-Mn$_2$O$_3$ indicates that HP-HT conditions can induce a charge disproportionation in simple transition-metal oxides A$_2$O$_3$, and potentially various mixed-valence polymorphs of these oxides, for example, with ilmenite-type, LiNbO$_3$-type, perovskite-type, and other structures, could be stabilized at HP-HT conditions

High-pressure synthesis of seven lanthanum hydrides with a significant variability of hydrogen content

The lanthanum-hydrogen system has attracted significant attention following the report of superconductivity in LaH10 at near-ambient temperatures and high pressures. Phases other than LaH10 are suspected to be synthesized based on both powder X-ray diffraction and resistivity data, although they have not yet been identified. Here, we present the results of our single-crystal X-ray diffraction studies on this system, supported by density functional theory calculations, which reveal an unexpected chemical and structural diversity of lanthanum hydrides synthesized in the range of 50 to 180 GPa. Seven lanthanum hydrides were produced, LaH3, LaH~4, LaH4+δ, La4H23, LaH6+δ, LaH9+δ, and LaH10+δ, and the atomic coordinates of lanthanum in their structures determined. The regularities in rare-earth element hydrides unveiled here provide clues to guide the search for other synthesizable hydrides and candidate high-temperature superconductors. The hydrogen content variability in lanthanum hydrides and the samples’ phase heterogeneity underline the challenges related to assessing potentially superconducting phases and the nature of electronic transitions in high-pressure hydrides.Funding: Alexander von Humboldt Foundation; Deutsche Forschungsgemeinschaft (DFG) [LA-4916/1-1, DU 954-11/1, DU 393-9/2, DU 393-13/1, DFG FOR2125, WI1232]; UKRI Future Leaders Fellowship [MR/V025724/1]; Federal Ministry of Education and Research, Germany (BMBF) [05K19WC1]; BIOVIA through the Science Ambassador program; Swedish Government Strategic Research Area inMaterials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009 00971]; Knut and Alice Wallenberg Foundation [KAW-2018.0194]; Swedish e-science Research Center (SeRC); Swedish Research Council (VR) grant [2019-05600]; Swedish Research Council (VR) program [2020-04630]; Swedish e-Science ResearchCentre (SeRC)</p

Novel Class of Rhenium Borides Based on Hexagonal Boron Networks Interconnected by Short B-2 Dumbbells

Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3) and rhenium tetraboride (ReB4) consist of close-packed single layers of rhenium atoms alternating with boron networks built from puckered hexagonal layers, which link short bonded (similar to 1.7 angstrom) axially oriented B-2 dumbbells. The short and incompressible Re-B and B-B bonds oriented along the hexagonal c-axis contribute to low axial compressibility comparable with the linear compressibility of diamond. Sub-millimeter samples of ReB3 and ReB4 were synthesized in a large-volume press at pressures as low as 33 GPa and used for material characterization. Crystals of both compounds are metallic and hard (Vickers hardness, H-V = 34(3) GPa). Geometrical, crystal-chemical, and theoretical analysis considerations suggest that potential ReBx compounds with x &amp;gt; 4 can be based on the same principle of structural organization as in ReB3 and ReB4 and possess similar mechanical and electronic properties.Funding Agencies|Carnegie Institution of Washington; Promotion of Equal Opportunities for Women in Research and Teaching? - Free State of Bavaria; Deutsche Forschungsgemeinschaft [BY112/2-1]; National Science Foundation-Earth Sciences [EAR-1634415]; Department of Energy-GeoSciences [DE-FG02-94ER14466]; U.S. Department of Energy (DOE) Office of Science [DE-AC02-06CH11357]; European Research Council (ERC) [949626]; Knut and Alice Wallenberg (KAW) Foundation [KAW 2015.0043]; Swedish Research Council (VR) [2014-6336, 2019-05403, 2019-05600]; program Promotion of Equal Opportunities for Women in Research and Teaching - Free State of Bavaria; Swedish Government Strategic Research Areasin Materials Scienceon Functional Materials at Linkoeping University [2009 00971]; DOE - NNSAs Office of Experimental Sciences; Marie Sklodowska Curie Actions [INCA 600398]; Knut and Alice Wallenberg Foundation (Wallenberg Scholar Grant) [KAW-2018.0194]; Swedish Foundation for Strategic Research [FFL 15-0290]; European Research Council (ERC)</p

Unraveling the Bonding Complexity of Polyhalogen Anions: High-Pressure Synthesis of Unpredicted Sodium Chlorides Na2_2Cl3_3 and Na4_4Cl5_5 and Bromide Na4_4Br5_5

The field of polyhalogen chemistry, specifically polyhalogen anions (polyhalides), is rapidly evolving. Here, we present the synthesis of three sodium halides with unpredicted chemical compositions and structures (tP10-Na$_2$Cl$_3$, hP18-Na$_4$Cl$_5$, and hP18-Na$_4$Br$_5$), a series of isostructural cubic cP8-AX$_3$ halides (NaCl$_3$, KCl$_3$, NaBr$_3$, and KBr$_3$), and a trigonal potassium chloride (hP24-KCl$_3$). The high-pressure syntheses were realized at 41–80 GPa in diamond anvil cells laser-heated at about 2000 K. Single-crystal synchrotron X-ray diffraction (XRD) provided the first accurate structural data for the symmetric trichloride Cl3– anion in hP24-KCl3 and revealed the existence of two different types of infinite linear polyhalogen chains, [Cl]$_∞$$^{n–}$ and [Br]$_∞$$^{n–}$, in the structures of cP8-AX$_3$ compounds and in hP18-Na$_4$Cl$_5$ and hP18-Na$_4$Br$_5$. In Na$_4$Cl$_5$ and Na$_4$Br$_5$, we found unusually short, likely pressure-stabilized, contacts between sodium cations. Ab initio calculations support the analysis of structures, bonding, and properties of the studied halogenides

Novel Class of Rhenium Borides Based on Hexagonal Boron Networks Interconnected by Short B-2 Dumbbells

Transition metal borides are known due to their attractive mechanical, electronic, refractive, and other properties. A new class of rhenium borides was identified by synchrotron single-crystal X-ray diffraction experiments in laser-heated diamond anvil cells between 26 and 75 GPa. Recoverable to ambient conditions, compounds rhenium triboride (ReB3) and rhenium tetraboride (ReB4) consist of close-packed single layers of rhenium atoms alternating with boron networks built from puckered hexagonal layers, which link short bonded (similar to 1.7 angstrom) axially oriented B-2 dumbbells. The short and incompressible Re-B and B-B bonds oriented along the hexagonal c-axis contribute to low axial compressibility comparable with the linear compressibility of diamond. Sub-millimeter samples of ReB3 and ReB4 were synthesized in a large-volume press at pressures as low as 33 GPa and used for material characterization. Crystals of both compounds are metallic and hard (Vickers hardness, H-V = 34(3) GPa). Geometrical, crystal-chemical, and theoretical analysis considerations suggest that potential ReBx compounds with x > 4 can be based on the same principle of structural organization as in ReB3 and ReB4 and possess similar mechanical and electronic properties