In‐Cage Interactions in the Clathrate Superconductor Sr<sub>8</sub>Si<sub>46</sub>

Hübner, Julia‐Maria; Prots, Yurii; Schnelle, Walter; Bobnar, Matej; König, Markus; Baitinger, Michael; Simon, Paul; Carrillo‐Cabrera, W.; Ormeci, Alim; Svanidze, Eteri; Grin, Yuri; Schwarz, Ulrich

doi:10.1002/chem.201904170

Cited by 21 publications

(22 citation statements)

References 73 publications

(169 reference statements)

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“…Furthermore, the effective charge of hafnium, evaluated by integration over the electron density within the region formed by zero-flux surfaces in its gradient field around the nucleus of Hf, is unexpectedly large (+1.83). It is essentially larger than even the charges of the filler atoms Ba (from +1.1 to +1.4 89 ) and Sr (from +1.34 to +1.54 90 , 91 ) in intermetallic clathrates. This fact allows us to assume strongly polar interactions of hafnium with its ligands.…”

Section: Resultsmentioning

confidence: 95%

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ

et al. 2020

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Hf 2 B 2–2δ Ir 5+δ crystallizes with a new type of structure: space group Pbam , a = 5.6300(3) Å, b = 11.2599(5) Å, and c = 3.8328(2) Å. Nearly 5% of the boron pairs are randomly replaced by single iridium atoms (Ir 5+δ B 2–2δ ). From an analysis of the chemical bonding, the crystal structure can be understood as a three-dimensional framework stabilized by covalent two-atom B–B and Ir–Ir as well as three-atom Ir–Ir–B and Ir–Ir–Ir interactions. The hafnium atoms center 14-atom cavities and transfer a significant amount of charge to the polyanionic boron–iridium framework. This refractory boride displays moderate hardness and is a Pauli paramagnet with metallic electrical resistivity, Seebeck coefficient, and thermal conductivity. The metallic character of this system is also confirmed by electronic structure calculations revealing 5.8 states eV –1 fu –1 at the Fermi level. Zr 2 B 2–2δ Ir 5+δ is found to be isotypic with Hf 2 B 2–2δ Ir 5+δ , and both form a continuous solid solution.

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Section: Resultsmentioning

confidence: 95%

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ

et al. 2020

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“…In addition, other advanced preparation techniques are still expanding the number of accessible binary clathrate phases. [4,7,8,11,33,45,[54][55][56] High-resolution X-ray diffraction in combination with modern microstructure analysis involving high-resolution transmission-electron microscopy and electron diffraction will grant access to hitherto unrecognized superstructures featuring unprecedented vacancy patterns. Last but not least, the finding that Li atoms occupy framework positions rather than cage centers raises hopes that understanding the nature of Zintl defects paves the way for the preparation of novel clathrates, e.g., with rare-earth metals.…”

Section: Discussionmentioning

confidence: 99%

“…The preparation of vacancy clathrate‐I compounds by low‐temperature redox reactions is expected to open a route to unique metastable clathrate‐I phases. In addition, other advanced preparation techniques are still expanding the number of accessible binary clathrate phases , , , , , . High‐resolution X‐ray diffraction in combination with modern microstructure analysis involving high‐resolution transmission‐electron microscopy and electron diffraction will grant access to hitherto unrecognized superstructures featuring unprecedented vacancy patterns.…”

Section: Discussionmentioning

confidence: 99%

“…This finding has been subsequently utilized for the analysis of in-cage Si-Sr bonding in (Sr 2+ ) 8 Si 46 ϫ 16 e -. [45] No total ELI-D maxima were found between Si and Sr atoms. However, the partial ELI-D diagram using only the filled 8 orbitals per formula unit above the empty Si 46 electron count yields maxima of the pELI-D inside the cages, indicating multiatomic Si-Sr in-cage interactions concealed in the total ELI-D.…”

Section: Substitution Vacancies and Lewis Acidsmentioning

confidence: 96%

“…A more in‐depth analysis with the orbital‐resolved partial‐ELI‐D tool revealed that the observed T –Ba ELI‐D attractors are created by bands in the specific energy range just below the Fermi level, in which the Ba(5d) states become increasingly occupied, and T ( n d) contributions remain lower than 10 states per eV. This finding has been subsequently utilized for the analysis of in‐cage Si–Sr bonding in (Sr 2+ ) 8 Si 46 × 16 e – . No total ELI‐D maxima were found between Si and Sr atoms.…”

Section: Substitution Vacancies and Lewis Acidsmentioning

confidence: 99%

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Zintl Defects in Intermetallic Clathrates

Baitinger¹,

Böhme²,

Wagner³

et al. 2020

Zeitschrift anorg allge chemie

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In many cases, idealized crystal structure models cannot rationalize the actual properties of intermetallic compounds. For a realistic approach in materials research, microstructures and defects need to be taken into account. In case of clathrate compounds, particularly the intrinsic framework vacancies (denoted as Zintl defects) demand consideration. Consequently, clathrate research produces evidence that modern‐day structure chemistry involves the utilization of advanced X‐ray diffraction methods combined with elaborated bulk phase analyses, the investigation of phase relations, and the study of mutual interrelations in the triangle chemical bonding–structure–properties. Herein, we review some fundamental contributions to the specific defect chemistry of intermetallic clathrates.

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Structural Origin of Reversible Li Insertion in Guest‐Free, Type‐II Silicon Clathrates

Dopilka

Weller

Ovchinnikov

et al. 2021

Adv Energy and Sustain Res

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Tetrel (Tt ¼ Si, Ge, Sn) clathrates are host-guest materials comprising cage frameworks of Tt elements that encapsulate alkali metal and alkaline earth metal guest atoms. Well known as promising candidates for thermoelectric materials, [1] clathrates also have interesting properties for optoelectronics [2][3][4] and superconducting [5][6][7] applications. Due to the large interest in Tt elements as high-capacity Li-ion battery anodes, the electrochemical properties of Tt clathrates have also been investigated in recent years, revealing properties distinct from those of diamond cubic structured analogues. [8][9][10][11][12][13][14][15][16][17][18] For instance, the reaction of Li with the type-I clathrate Ba 8 Al 16 Si 30 is dominated by surface rather than bulk reactions, [15] whereas the Ba 8 Al y Ge 46-y (0 < y < 16) clathrate undergoes bulk phase transitions to form amorphous Li-Ba-Ge phases with local structures similar to those in Li-Ge crystalline phases. [10,16] For the type-II clathrate Na 24 Si 136 , the lithiation profile is similar to that for diamond cubic Si, [12] whereas Na 1.6 Si 136 displays one more similar to that of amorphous Si. [8] Due to the wide range of possible clathrate structures and compositions, [1] we are interested in establishing a better understanding of the structure-property relationships of clathrates within the context of Li-ion battery applications.Clathrates crystallize in a variety of structural types where different face-sharing polyhedra are built from tetrahedral bonding

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In‐Cage Interactions in the Clathrate Superconductor Sr₈Si₄₆

Cited by 21 publications

References 73 publications

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ

Zintl Defects in Intermetallic Clathrates

Structural Origin of Reversible Li Insertion in Guest‐Free, Type‐II Silicon Clathrates

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In‐Cage Interactions in the Clathrate Superconductor Sr8Si46

Cited by 21 publications

References 73 publications

Crystal Structure and Physical Properties of the Cage Compound Hf2B2–2δIr5+δ

Crystal Structure and Physical Properties of the Cage Compound Hf2B2–2δIr5+δ

Zintl Defects in Intermetallic Clathrates

Structural Origin of Reversible Li Insertion in Guest‐Free, Type‐II Silicon Clathrates

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In‐Cage Interactions in the Clathrate Superconductor Sr₈Si₄₆

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ

Crystal Structure and Physical Properties of the Cage Compound Hf₂B_2–2δIr_5+δ