| 1. |
- Baranets, Sviatoslav, et al.
(författare)
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Complex Structural Disorder in the Zintl Phases Yb10MnSb9 and Yb21Mn4Sb18
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:9, s. 6702-6711
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Tidskriftsartikel (refereegranskat)abstract
- A systematic investigation of the ternary system Yb-Mn-Sb led to the discovery of the novel phase Yb10MnSb9. Its crystal structure was characterized by single-crystal X-ray diffraction and found to be complex and highly disordered. The average Yb10MnSb9 structure can be considered to represent a defect modification of the Ca10LiMgSb9 type and to crystallize in the tetragonal P4(2)/mnm space group (No. 136) with four formula units per cell. The structural disorder can be associated with both occupational and positional effects on several Yb and Mn sites. Similar traits were observed for the structure of the recently reported Yb21Mn4Sb18 phase (monoclinic space group C2/c, No. 15), which was reevaluated as part of this study as well. In both structures, distorted Sb-6 octahedra centered by Yb atoms and Sb-4 tetrahedra centered by Mn atoms form disordered fragments, which appear as the hallmark of the structural chemistry in this system. Discussion along the lines of how difficult, and important, it is to distinguish Yb10MnSb9 from the compositionally similar binary Yb11Sb10 and ternary Yb14MnSb11 compounds is also presented. Preliminary transport measurements for polycrystalline Yb10MnSb9 indicate high values of the Seebeck coefficient, approaching 210 mu V K-1 at 600 K, and a semiconducting behavior with a room-temperature resistivity of 114 m Omega cm.
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| 2. |
- Baranets, Sviatoslav, et al.
(författare)
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Structural Uniqueness of the [Nb(As5)2]5– Cluster in the Zintl Phase Cs5NbAs10
- 2021
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 125:20, s. 4323-4333
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the novel Zintl phase, Cs5NbAs10, is reported for the first time. This compound crystallizes in the monoclinic P21/c space group (no. 14) with eight formula units per cell. The structure represents a unique atomic arrangement, constituting a new structure type with Wyckoff sequence e32. The most important structural element is the unprecedented [Nb(As5)2]5– cluster anion, formed by a Nb atom enclosed between two As5 rings. These nonaromatic cyclic species, formally [As5]5–, adopt an envelope conformation similar to that of cyclopentane. To date, it is only the second example of an [As5]5– ring with this conformation, reported in an inorganic solid-state compound. The bonding characteristics of the [Nb(As5)2]5– cluster and the [As5]5– rings are thoroughly investigated using first-principles methods and discussed. Electronic band structure calculations on Cs5NbAs10 suggest that this compound is a semiconductor with an estimated band gap of ca. 1.4 eV.
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| 3. |
- Baranets, Sviatoslav, et al.
(författare)
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Synthesis, crystal and electronic structure of BaLi2Cd2Ge2
- 2021
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Ingår i: Zeitschrift für Naturforschung. B, A journal of chemical sciences. - : Walter de Gruyter GmbH. - 0932-0776 .- 1865-7117. ; 76:10-12, s. 689-697
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Tidskriftsartikel (refereegranskat)abstract
- A new quatemary germanide has been synthesized and structurally characterized. BaLi2Cd2Ge2 adopts the rhombohedral CaCu4P2 structure type (Pearson code hR7; space group R (3) over barm, Z = 3) with unit cell parameters a = 4.5929(6) and c= 26.119(5) angstrom. Structure refinements from single-crystal X-ray diffraction data demonstrate that the layered crystal structure can be regarded as an ordered quaternary variant of the ternary archetype; structural parallels to layered pnictides and binary germanides can also be drawn. The layered crystal structure is characterized by the absence of direct Ge-Ge and Cd-Cd homoatomic bonds, which suggests that BaLi2Cd2Ge2 should be classified as a Zintl phase, according to the formulation (BA(2+))(Li+)(2) (Cd2+)(2)(Ge-4(-))(2). Electronic structure calculations show that the Fermi level crosses a distinct peak in the DOS, although the presence of an electronic band gap or a dip in the electronic density of states at the Fermi level is expected based on the electron partitioning.
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| 4. |
- Dopilka, Andrew, et al.
(författare)
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Structural and Electrochemical Properties of Type VIII Ba8Ga16−δSn30+δClathrate (δ≈1) during Lithiation
- 2021
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 13:36, s. 42564-42578
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Tidskriftsartikel (refereegranskat)abstract
- Clathrates of the tetrel (Tt = Si, Ge, Sn) elements are host-guest structures that can undergo Li alloying reactions with high capacities. However, little is known about how the cage structure affects the phase transformations that take place during lithiation. To further this understanding, the structural changes of the type VIII clathrate Ba8Ga16-delta Sn30+delta (delta approximate to 1) during lithiation are investigated and compared to those in beta-Sn with ex situ X-ray total scattering measurements and pair distribution function (PDF) analysis. The results show that the type VIII clathrate undergoes an alloying reaction to form Li-rich amorphous phases (LixBa0.17Ga0.33Sn0.67, x = 2-3) with local structures similar to those in the crystalline binary Li-Sn phases that form during the lithiation of beta-Sn. As a result of the amorphous phase transition, the type VIII clathrate reacts at a lower voltage (0.25 V vs Li/Li+) compared to beta-Sn (0.45 V) and goes through a solid-solution reaction after the initial conversion of the crystalline clathrate phase. Cycling experiments suggest that the amorphous phase persists after the first lithiation and results in considerably better cycling than in beta-Sn. Density functional theory (DFT) calculations suggest that topotactic Li insertion into the clathrate lattice is not favorable due to the high energy of the Li sites, which is consistent with the experimentally observed amorphous phase transformation. The local structure in the clathrate featuring Ba atoms surrounded by a cage of Ga and Sn atoms is hypothesized to kinetically circumvent the formation of Li-Sn or Li-Ga crystalline phases, which results in better cycling and a lower reaction voltage. Based on the improved electrochemical performance, clathrates could act as tunable precursors to form amorphous Li alloying phases with novel electrochemical properties.
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| 5. |
- Dopilka, Andrew, et al.
(författare)
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Structural Origin of Reversible Li Insertion in Guest-Free, Type-II Silicon Clathrates
- 2021
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Ingår i: Advanced energy and sustainability research. - : Wiley. - 2699-9412. ; 2:5
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Tidskriftsartikel (refereegranskat)abstract
- The guest-free, type-II Si clathrate (Si136) is an open cage polymorph of Si with structural features amenable to electrochemical Li storage. However, the detailed mechanism for reversible Li insertion and migration within the vacant cages of Si136 is not established. Herein, X-ray characterization and density functional theory (DFT) calculations are used to understand the structural origin of electrochemical Li insertion into the type-II clathrate structure. At low Li content, instead of alloying with Si, topotactic Li insertion into the empty cages occurs at ≈0.3 V versus Li/Li+ with a capacity of ≈231 mAh g−1 (corresponding to composition Li32Si136). A synchrotron powder X-ray diffraction analysis of electrodes after lithiation shows evidence of Li occupation within the Si20 and Si28 cages and a volume expansion of 0.22%, which is corroborated by DFT calculations. Nudged elastic band calculations suggest a low barrier (0.2 eV) for Li migration through interconnected Si28 cages, whereas there is a higher barrier for Li migration into Si20 cages (2.0 eV). However, if Li is present in a neighboring cage, a cooperative migration pathway with a barrier of 0.65 eV is possible. The results show that the type-II Si clathrate displays unique electrochemical properties for potential applications as Li-ion battery anodes.
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| 6. |
- Dopilka, Andrew, et al.
(författare)
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Synthesis of Type II Ge and Ge–Si Alloyed Clathrates Using Solid-State Electrochemical Oxidation of Zintl Phase Precursors
- 2022
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 61:31, s. 12363-12372
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Tidskriftsartikel (refereegranskat)abstract
- Germanium clathrates with the type II structure are open-framework materials that show promise for various applications, but the difficulty of achieving phase-pure products via traditional synthesis routes has hindered their development. Herein, we demonstrate the synthesis of type II Ge clathrates in a two-electrode electrochemical cell using Na4Ge4–ySiy (y = 0, 1) Zintl phase precursors as the working electrode, Na metal as the counter/reference electrode, and Na-ion conducting β″-alumina as the solid electrolyte. The galvanostatic oxidation of Na4Ge4 resulted in voltage plateaus around 0.34–0.40 V vs Na/Na+ with the formation of different products depending on the reaction temperature. When using Na4Ge3Si as a precursor, nearly phase-pure, alloyed type II Ge–Si clathrate was obtained at 350 °C. The Na atoms in the large (Ge,Si)28 cages of the clathrate occupied off-centered positions according to Rietveld refinement and density functional theory calculations. The results indicate that electrochemical oxidation of Zintl phase precursors is a promising pathway for synthesizing Ge clathrates with type II structure and that Si alloying of the Zintl phase precursor can promote selective clathrate product formation over other phases.
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| 7. |
- Ovchinnikov, Alexander, et al.
(författare)
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Bismuth as a Reactive Solvent in the Synthesis of Multicomponent Transition-Metal-Bearing Bismuthides
- 2020
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 59:6, s. 3459-3470
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Tidskriftsartikel (refereegranskat)abstract
- Employment of liquid bismuth (Bi) allows the facile single-crystal growth of compounds containing elements with high melting points, provided that these elements have reasonably high solubility in Bi. Utilization of the Bi flux approach yielded two new ternary bismuthides, SrNi0.17(1) Bi-2[a defect variant of the BaCuSn2 type, space group Cmcm, a = 4.879(2) angstrom, b = 17.580(6) angstrom, and c = 4.696(2) angstrom] and CaTi3Bi4 [NdTi3 (Sn0.1Sb0.9)(4) structure type, space group Fmmm, a = 5.6295(7) angstrom, b = 9.8389(1) angstrom, and c = 23.905(3) angstrom]. In addition, the ternary antimonide CaV3Sb4, isostructural with CaTi3Bi4, was synthesized from antimony (Sb) flux, and analyzed with the goal of validating structural assessment of the bismuthide analogue, where the X-ray crystallographic work proved to be very challenging. All synthesized compounds exhibit complex crystal structures featuring quasi-two-dimensional building blocks of different topologies. First-principle calculations reveal hypervalent bonding in the homoatomic Bi subunits. Physical property measurements indicate metallic conductivity and the absence of localized magnetism in the studied compounds.
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| 8. |
- Ovchinnikov, Alexander, et al.
(författare)
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Electronic stabilization by occupational disorder in the ternary bismuthide Li3-x-yInxBi (x similar or equal to 0.14, y similar or equal to 0.29)
- 2020
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Ingår i: Acta crystallographica. Section C, Structural chemistry. - 2053-2296. ; 76, s. 585-590
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Tidskriftsartikel (refereegranskat)abstract
- A ternary derivative of Li3Bi with the composition Li3-x-yInxBi (x similar or equal to 0.14, y similar or equal to 0.29) was produced by a mixed In+Bi flux approach. The crystal structure adopts the space group Fd (3) over barm (No. 227), with a = 13.337 (4) angstrom, and can be viewed as a 2 x 2 x 2 superstructure of the parent Li3Bi phase, resulting from a partial ordering of Li and In in the tetrahedral voids of the Bi fcc packing. In addition to the Li/In substitutional disorder, partial occupation of some Li sites is observed. The Li deficiency develops to reduce the total electron count in the system, counteracting thereby the electron doping introduced by the In substitution. First-principles calculations confirm the electronic rationale of the observed disorder.
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| 9. |
- Ovchinnikov, Alexander, et al.
(författare)
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Exploration of Multi-Component Vanadium and Titanium Pnictides Using Flux Growth and Conventional High-Temperature Methods
- 2020
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Ingår i: Frontiers in Chemistry. - : Frontiers Media SA. - 2296-2646. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The flux growth method was successfully employed to synthesize millimeter-sized single crystals of the ternary barium vanadium pnictides Ba5V12As19+x (x approximate to 0.02) and Ba5V12Sb19+x (x approximate to 0.36), using molten Pb and Sb, respectively. Both compositions crystallize in space group P43m and adopt a structure similar to those of the barium titanium pnictides Ba(5)Ti(12)Pn(19+x) (Pn = Sb, Bi), yet with a subtly different disorder, involving the pnictogen and barium atoms. Attempts to obtain an arsenide analog of Ba(5)Ti(12)Pn(19+x) using a Pb flux technique yielded binary arsenides. High-temperature treatment of the elements Ba, Ti, and As in Nb or Ta tubes resulted in side reactions with the crucible materials and produced two isostructural compositions Ba8Ti13-xMxAs21 (M = Nb, Ta; x approximate to 4), representing a new structure type. The latter structure displays fcc-type metal clusters comprised of statistically distributed Ti and M atoms (M = Nb, Ta) with multi-center and two-center bonding within the clusters, as suggested by our first-principle calculations.
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| 10. |
- Ovchinnikov, Alexander, et al.
(författare)
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Layered Quaternary Germanides-Synthesis and Crystal and Electronic Structures of AELi(2)In(2)Ge(2) (AE = Sr, Ba, Eu)
- 2019
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 58:12, s. 7895-7904
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Tidskriftsartikel (refereegranskat)abstract
- Three new quaternary germanides with the composition AELi(2)In(2)Ge(2) (AE = Sr, Ba, Eu) have been synthesized and structurally characterized. The layered crystal structure of these phases features homoatomic In-In bonding, but there are no direct Ge-Ge bonds. Such a crystallographic arrangement can be regarded as an ordered quaternary derivative of the CaCu4P2 structure (trigonal syngony, Pearson code hR7). Comprehensive analysis of the structural genealogy suggests relationships with the structures of other layered pnictides and chalcogenides, which are discussed. Partitioning of the available valence electrons and the assignment of the formal charges indicate that the composition of the new germanides is charge-balanced. First-principles calculations and electrical transport measurements indicate poor metallic behavior, resulting from significant hybridization of the electronic states.
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