| 1. |
- Bykov, Maxim, et al.
(författare)
-
High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re-2(N-2)(N)(2) stable at ambient conditions
- 2019
-
Ingår i: Nature Communications. - : NATURE PUBLISHING GROUP. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- 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 (K-0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re-2(N-2)(N)(2). Unlike known transition metals pernitrides Re-2(N-2)(N)(2) contains both pernitride N-2(4-) and discrete N3- anions, which explains its exceptional properties. Re-2(N-2)(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 ambient 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, Re-2(N-2)(N)(2) turned to be at a threshold for superhard materials.
|
|
| 2. |
- Efthimiopoulos, Ilias, et al.
(författare)
-
Structural transformations of Li2C2 at high pressures
- 2015
-
Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 92:6
-
Tidskriftsartikel (refereegranskat)abstract
- Structural changes of Li2C2 under pressure were studied by synchrotron x-ray diffraction in a diamond anvilcell under hydrostatic conditions and by using evolutionary search methodology for crystal structure prediction.We show that the high-pressure polymorph of Li2C2, which forms from the Immm ground-state structure (Z = 2)at around 15 GPa, adopts an orthorhombic Pnma structure with Z = 4. Acetylide C2 dumbbells characteristic ofImmm Li2C2 are retained in Pnma Li2C2. The structure of Pnma Li2C2 relates closely to the anticotunnite-typestructure. C2 dumbbell units are coordinated by nine Li atoms, as compared to eight in the antifluorite structureof Immm Li2C2. First-principles calculations predict a transition of Pnma Li2C2 at 32 GPa to a topologicallyidentical phase with a higher Cmcm symmetry. The coordination of C2 dumbbell units by Li atoms is increasedto 11. The structure of Cmcm Li2C2 relates closely to the Ni2 In-type structure. It is calculated that Cmcm Li2C2becomes metallic at pressures above 40 GPa. In experiments, however, Pnma Li2C2 is susceptible to irreversibleamorphization.
|
|
| 3. |
- Serovaiskii, Aleksandr, et al.
(författare)
-
Fate of Hydrocarbons in Iron-Bearing Mineral Environments during Subduction
- 2019
-
Ingår i: Minerals. - : MDPI. - 2075-163X. ; 9:11
-
Tidskriftsartikel (refereegranskat)abstract
- Subducted sediments play a key role in the evolution of the continental crust and upper mantle. As part of the deep carbon cycle, hydrocarbons are accumulated in sediments of subduction zones and could eventually be transported with the slab below the crust, thus affecting processes in the deep Earth's interior. However, the behavior of hydrocarbons during subduction is poorly understood. We experimentally investigated the chemical interaction of model hydrocarbon mixtures or natural oil with ferrous iron-bearing silicates and oxides (representing possible rock-forming materials) at pressure-temperature conditions of the Earth's lower crust and upper mantle (up to 2000(+/- 100) K and 10(+/- 0.2) GPa), and characterized the run products using Raman and Mossbauer spectroscopies and X-ray diffraction. Our results demonstrate that complex hydrocarbons are stable on their own at thermobaric conditions corresponding to depths exceeding 50 km. We also found that chemical reactions between hydrocarbons and ferrous iron-bearing rocks during slab subduction lead to the formation of iron hydride and iron carbide. Iron hydride with relatively low melting temperature may form a liquid with negative buoyancy that could transport reduced iron and hydrogen to greater depths.
|
|
