| 1. |
- Aslandukova, Alena, et al.
(författare)
-
High-pressure hP3 yttrium allotrope with CaHg2-type structure as a prototype of the hP3 rare-earth hydride series
- 2023
-
Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 107:1
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 2. |
- Bykova, Elena, et al.
(författare)
-
Synthesis, crystal structure, and properties of stoichiometric hard tungsten tetraboride, WB4
- 2022
-
Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 10:37, s. 20111-20120
-
Tidskriftsartikel (refereegranskat)abstract
- Tungsten tetraboride has been known so far as a non-stoichiometric compound with a variable composition (e.g. WB4-x, WB4+x). Its mechanical properties could exceed those of hard tungsten carbide, which is widely used nowadays in science and technology. The existence of stoichiometric WB4 has not been proven yet, and its structure and crystal chemistry remain debatable to date. Here we report the synthesis of single crystals of the stoichiometric WB4 phase under high-pressure high-temperature conditions. The crystal structure of WB4 was determined using synchrotron single-crystal X-ray diffraction. In situ high-pressure compressibility measurements show that the bulk modulus of WB4 is 238.6(2) GPa for B = 5.6(0). Measurements of mechanical properties of bulk polycrystalline sub-millimeter size samples under ambient conditions reveal a hardness of similar to 36 GPa, confirming that the material falls in the category of superhard materials.
|
|
| 3. |
- Gorelova, Liudmila, et al.
(författare)
-
Edge-sharing BO4 tetrahedra and penta-coordinated silicon in the high-pressure modification of NaBSi3O8
- 2022
-
Ingår i: Inorganic Chemistry Frontiers. - : ROYAL SOC CHEMISTRY. - 2052-1545 .- 2052-1553. ; 9:8, s. 1735-1742
-
Tidskriftsartikel (refereegranskat)abstract
- The high-pressure behavior of the borosilicate reedmergnerite NaBSi3O8 has been studied using in situ single-crystal X-ray diffraction and Raman spectroscopy up to 35 GPa. The crystal structure of NaBSi3O8 contracts homogeneously upon compression up to 12 GPa, while at higher pressures it undergoes two phase transitions. Above 16 GPa the unit-cell volume is doubled, whereas the coordination numbers of all cations and the structural topology are preserved. Above 25 GPa the crystal structure of NaBSi3O8 contains extremely rare dimers of edge-sharing BO4 tetrahedra and earlier unknown Si2O5 groups consisting of edge-sharing SiO5 square pyramids. The structural model was corroborated by DFT calculations. This HP modification results in the first example of a borosilicate compound with edge-sharing BO4 tetrahedra.
|
|
| 4. |
- Khandarkhaeva, Saiana, et al.
(författare)
-
Structural Diversity of Magnetite and Products of Its Decomposition at Extreme Conditions
- 2022
-
Ingår i: Inorganic Chemistry. - : AMER CHEMICAL SOC. - 0020-1669 .- 1520-510X. ; 61:2, s. 1091-1101
-
Tidskriftsartikel (refereegranskat)abstract
- Magnetite, Fe3O4, is the oldest known magnetic mineral and archetypal mixed-valence oxide. Despite its recognized role in deep Earth processes, the behavior of magnetite at extreme high-pressure high-temperature (HPHT) conditions remains insufficiently studied. Here, we report on single-crystal synchrotron X-ray diffraction experiments up to similar to 80 GPa and 5000 K in diamond anvil cells, which reveal two previously unknown Fe3O4 polymorphs, gamma-Fe3O4 with the orthorhombic Yb3S4-type structure and delta-Fe3O4 with the modified Th3P4-type structure. The latter has never been predicted for iron compounds. The decomposition of Fe3O4 at HPHT conditions was found to result in the formation of exotic phases, Fe5O7 and Fe25O32, with complex structures. Crystal-chemical analysis of iron complex Crystal-chemical analysis oxides suggests the high-spin to low-spin crossover in octahedrally coordinated Fe3+ in the pressure interval between 43 and 51 GPa. Our experiments demonstrate that HPHT conditions promote the formation of ferric-rich Fe-O compounds, thus arguing for the possible involvement of magnetite in the deep oxygen cycle.
|
|
| 5. |
- Laniel, Dominique, et al.
(författare)
-
Aromatic hexazine [N6]4− anion featured in the complex structure of the high-pressure potassium nitrogen compound K9N56
- 2023
-
Ingår i: Nature Chemistry. - : NATURE PORTFOLIO. - 1755-4330 .- 1755-4349. ; 15:5, s. 641-646
-
Tidskriftsartikel (refereegranskat)abstract
- The recent high-pressure synthesis of pentazolates and the subsequent stabilization of the aromatic [N-5](-) anion at atmospheric pressure have had an immense impact on nitrogen chemistry. Other aromatic nitrogen species have also been actively sought, including the hexaazabenzene N-6 ring. Although a variety of configurations and geometries have been proposed based on ab initio calculations, one that stands out as a likely candidate is the aromatic hexazine anion [N-6](4-). Here we present the synthesis of this species, realized in the high-pressure potassium nitrogen compound K9N56 formed at high pressures (46 and 61 GPa) and high temperature (estimated to be above 2,000 K) by direct reaction between nitrogen and KN3 in a laser-heated diamond anvil cell. The complex structure of K9N56-composed of 520 atoms per unit cell-was solved based on synchrotron single-crystal X-ray diffraction and corroborated by density functional theory calculations. The observed hexazine anion [N-6](4-) is planar and proposed to be aromatic.
|
|
| 6. |
- Laniel, Dominique, et al.
(författare)
-
Front Cover: Revealing Phosphorus Nitrides up to the Megabar Regime: Synthesis of α′-P3N5, δ-P3N5 and PN2 (Chem. Eur. J. 62/2022)
- 2022
-
Ingår i: Chemistry - A European Journal. - : Wiley-VCH Verlagsgesellschaft. - 0947-6539 .- 1521-3765. ; 28:62
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- For the last 30 years, the lack of a binary phosphorus nitride containing PN6 octahedra formed a scientific chasm between carbon-group and oxygen-group nitrides, both featuring a variety of solids with XN6 units (X being a non-metal element). Now, the discovery of the δ-P3N5 and PN2 phosphorus nitrides—formed under high pressure and both composed of the elusive PN6 octahedron—builds a long-sought-after bridge between these two groups of nitrides. More information can be found in the Research Article by D. Laniel, F. Trybel, and co-workers (DOI: 10.1002/chem.202201998).
|
|
| 7. |
- Laniel, Dominique, et al.
(författare)
-
Revealing Phosphorus Nitrides up to the Megabar Regime: Synthesis of α′‐P3N5, δ‐P3N5 and PN2
- 2022
-
Ingår i: Chemistry - A European Journal. - : WILEY-V C H VERLAG GMBH. - 0947-6539 .- 1521-3765. ; 28:62
-
Tidskriftsartikel (refereegranskat)abstract
- Non-metal nitrides are an exciting field of chemistry, featuring a significant number of compounds that can possess outstanding material properties. These properties mainly rely on maximizing the number of strong covalent bonds, with crosslinked XN6 octahedra frameworks being particularly attractive. In this study, the phosphorus-nitrogen system was studied up to 137 GPa in laser-heated diamond anvil cells, and three previously unobserved phases were synthesized and characterized by single-crystal X-ray diffraction, Raman spectroscopy measurements and density functional theory calculations. delta-P3N5 and PN2 were found to form at 72 and 134 GPa, respectively, and both feature dense 3D networks of the so far elusive PN6 units. The two compounds are ultra-incompressible, having a bulk modulus of K-0=322 GPa for delta-P3N5 and 339 GPa for PN2. Upon decompression below 7 GPa, delta-P3N5 undergoes a transformation into a novel alpha -P3N5 solid, stable at ambient conditions, that has a unique structure type based on PN4 tetrahedra. The formation of alpha -P3N5 underlines that a phase space otherwise inaccessible can be explored through materials formed under high pressure.
|
|
| 8. |
|
|
| 9. |
- Laniel, Dominique, et al.
(författare)
-
Synthesis of Ultra‐Incompressible and Recoverable Carbon Nitrides Featuring CN4 Tetrahedra
- 2024
-
Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 36:3
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
