Structural characterisations of the NaxSi136 and Na8Si46 silicon clathrates using the Rietveld method

Reny, E.; Gravereau, P.; Cros, C.

doi:10.1039/a804565h

Cited by 100 publications

(122 citation statements)

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“…Comparison of the evolution of selected features of the NaSi silicide and Na 8 Table 1). The -202 planes for NaSi pass through Na + sites that then become the centers of pentagonal dodecahedral and tetrakaidecahedral cage sites occupied by Na atoms in the clathrate structure.…”

Section: Single Temperature Ramp Experimentsmentioning

confidence: 99%

“…Studies on Ge and Sn clathrates gave rise to narrow gap semiconducting materials with compositions like K 8 Ge 44 or Rb 8 Sn 44 , where the metal oxidation is compensated by formation of vacancies in the clathrate framework. Compound clathrates such as Sr 8 Ga 16 Ge 30 have fully occupied frameworks and achieve charge balance by introduction of group 13 elements. Metal-deficient clathrates such as K 7 Si 46 are also known.…”

Section: Introductionmentioning

confidence: 99%

“…3,4,[16][17][18][19][20][21][22][23][24][25][26][27][28][29][30] Two main structural types were described during the initial studies of Si and Ge clathrate materials. [1][2][3][4][5][6][7][8][9] The type I clathrate has a primitive cubic structure (Pm3n: a o ~ 10.2 Å) based on dodecahedral [5 12 ] and tetrakaidecahedral [5 12 6 2 ] cages that are occupied by metal guest atoms to produce metallic Na 8 Si 46 whose formation is studied here. Studies on Ge and Sn clathrates gave rise to narrow gap semiconducting materials with compositions like K 8 Ge 44 or Rb 8 Sn 44 , where the metal oxidation is compensated by formation of vacancies in the clathrate framework.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9] The type I clathrate has a primitive cubic structure (Pm3n: a o ~ 10.2 Å) based on dodecahedral [5 12 ] and tetrakaidecahedral [5 12 6 2 ] cages that are occupied by metal guest atoms to produce metallic Na 8 Si 46 whose formation is studied here. Studies on Ge and Sn clathrates gave rise to narrow gap semiconducting materials with compositions like K 8 Ge 44 or Rb 8 Sn 44 , where the metal oxidation is compensated by formation of vacancies in the clathrate framework. Compound clathrates such as Sr 8 Ga 16 Ge 30 have fully occupied frameworks and achieve charge balance by introduction of group 13 elements.…”

Section: Introductionmentioning

confidence: 99%

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] The framework composed from sp 3 bonded atoms is intrinsically semiconducting. However the structures usually contain electropositive metal atoms located within the clathrate cages that inject electrons into the conduction band to produce metallic or narrow-gap semiconducting phases.…”

Section: Introductionmentioning

confidence: 99%

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Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

et al. 2011

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Silicon clathrates are unusual open-framework solids formed by tetrahedrally-bonded silicon that show remarkable electronic and thermal properties. The type I structure has a primitive cubic unit cell containing cages occupied by metal atoms to give compositions such as Na 8 Si 46 or Na 2 Ba 6 Si 46 . Although their structure and properties are well described there is little understanding of the formation mechanism. Na 8 Si 46 is typically produced by metastable thermal decomposition under vacuum conditions from NaSi, itself an unusual structure containing Si 4 4-poly-anions. In this study we used in situ synchrotron X-ray diffraction combined with rapid X-ray detection on samples taken through a controlled temperature ramp (25-500 o C at 8 o /min) under vacuum conditions (10 -4 bar), to study the clathrate formation reaction. We also carried out complementary in situ high temperature solid state 23 Na NMR experiments using a sealed tube loaded under inert gas atmosphere conditions. We find no evidence for an intermediate amorphous phase during clathrate formation. Instead we observe an unexpectedly high degree of structural coherency between the Na 8 Si 46 clathrate and its NaSi precursor, evidenced by a smooth passage of several X-ray reflections from one structure into the other. The results indicate the possibility of an unusual, epitaxial-like, growth of the clathrate phase as Na atoms are removed from the NaSi precursor into the vacuum.

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Section: Single Temperature Ramp Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

et al. 2011

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A Novel Technique for Controlling Anisotropic Ion Diffusion: Bulk Single‐Crystalline Metallic Silicon Clathrate

et al. 2022

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Na‐free Si clathrates consisting only of Si cages are an allotrope of diamond‐structured Si. This material is promising for various device applications, such as next‐generation photovoltaics. The probable technique for synthesizing Na‐free Si clathrates is to extract Na+ from the Si cages of Na24Si136. Vacuum annealing is presently a well‐known conventional and effective approach for extracting Na. However, this study demonstrates that Na+ cannot be extracted from the surface of a single‐crystalline type‐II metallic Si clathrate (Na24Si136) in areas deeper than 150 µm. Therefore, a novel method is developed to control anisotropic ion diffusion: this is effective for various compounds with a large difference in the bonding strength between their constituent elements, such as Na24Si136 composed of covalent Si cages and weakly trapped Na+. By skillfully exploiting the difference in the chemical potentials as a driving force, Na+ is homogeneously extracted regardless of the size of the single crystal while maintaining high crystallinity. Additionally, the proposed point defect model is evaluated via density functional theory, and the migration of Na+ between the Si cages is explained. It is expected that the developed experimental and computational techniques would significantly advance material design for synthesizing thermodynamically metastable materials.

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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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Structural characterisations of the NaxSi136 and Na8Si46 silicon clathrates using the Rietveld method

Cited by 100 publications

References 10 publications

Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

Time-Resolved in Situ Synchrotron X-ray Diffraction Studies of Type 1 Silicon Clathrate Formation

A Novel Technique for Controlling Anisotropic Ion Diffusion: Bulk Single‐Crystalline Metallic Silicon Clathrate

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

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