| 1. |
- Auer, Henry, et al.
(författare)
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The Hydrogenation of the Zintl Phase NdGa Studied by in situ Neutron Diffraction
- 2019
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 645:3, s. 175-181
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogenation of the Zintl phase NdGa was studied by in situ neutron powder diffraction. We find a compositional range of 0.1 < x < 0.8 in NdGaH1+x. Hydrogen atoms are located in two different positions, in HNd4 tetrahedra, and close to the polyanionic chains. For the latter, the Ga-H distance in NdGaH1.66 is quite long (ca. 200 pm) with a trigonal bipyramidal Nd3Ga2 surrounding of hydrogen atoms. Hydrogen poor NdGaH<1 phases as known for similar systems were not observed. The changing hydrogen content shows no measureable effect on the unit cell volume, but on lattice parameter ratios. Superstructures occur for 0.53 < x < 0.66 and 0.73 < x < 0.8, leading to a doubling or tripling of the lattice parameter a. They are probably caused by partial hydrogen ordering. The threefold superstructure contains a (1)[(Ga-H-Ga-H-Ga)(6-)] moiety with hydrogen bridging two gallium chains.
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| 2. |
- Spektor, Kristina, et al.
(författare)
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Hypervalent hydridosilicate in the Na-Si-H system
- 2023
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Ingår i: Frontiers in Chemistry. - : Frontiers Media S.A.. - 2296-2646. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogenation reactions at gigapascal pressures can yield hydrogen-rich materials with properties relating to superconductivity, ion conductivity, and hydrogen storage. Here, we investigated the ternary Na-Si-H system by computational structure prediction and in situ synchrotron diffraction studies of reaction mixtures NaH-Si-H-2 at 5-10 GPa. Structure prediction indicated the existence of various hypervalent hydridosilicate phases with compositions NamSiH(4+m) (m = 1-3) at comparatively low pressures, 0-20 GPa. These ternary Na-Si-H phases share, as a common structural feature, octahedral SiH62- complexes which are condensed into chains for m = 1 and occur as isolated species for m = 2, 3. In situ studies demonstrated the formation of the double salt Na-3[SiH6]H (Na3SiH7, m = 3) containing both octahedral SiH62- moieties and hydridic H-. Upon formation at elevated temperatures (>500 degrees C), Na3SiH7 attains a tetragonal structure (P4/mbm, Z = 2) which, during cooling, transforms to an orthorhombic polymorph (Pbam, Z = 4). Upon decompression, Pbam-Na3SiH7 was retained to approx. 4.5 GPa, below which a further transition into a yet unknown polymorph occurred. Na3SiH7 is a new representative of yet elusive hydridosilicate compounds. Its double salt nature and polymorphism are strongly reminiscent of fluorosilicates and germanates.
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| 3. |
- Vekilova, Olga, et al.
(författare)
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Formation and Polymorphism of Semiconducting K2SiH6 and Strategy for Metallization
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:21, s. 8093-8100
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Tidskriftsartikel (refereegranskat)abstract
- K2SiH6, crystallizing in the cubic K2PtCl6structure type (Fm3¯ m), features unusual hypervalent SiH62-complexes. Here, the formation of K2SiH6at high pressures is revisited by in situ synchrotron diffraction experiments, considering KSiH3as a precursor. At the investigated pressures, 8 and 13 GPa, K2SiH6adopts the trigonal (NH4)2SiF6structure type (P3¯ m1) upon formation. The trigonal polymorph is stable up to 725 °C at 13 GPa. At room temperature, the transition into an ambient pressure recoverable cubic form occurs below 6.7 GPa. Theory suggests the existence of an additional, hexagonal, variant in the pressure interval 3-5 GPa. According to density functional theory band structure calculations, K2SiH6is a semiconductor with a band gap around 2 eV. Nonbonding H-dominated states are situated below and Si-H anti-bonding states are located above the Fermi level. Enthalpically feasible and dynamically stable metallic variants of K2SiH6may be obtained when substituting Si partially by Al or P, thus inducing p- and n-type metallicity, respectively. Yet, electron-phonon coupling appears weak, and calculated superconducting transition temperatures are <1 K.
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