Investigation of substitution effects and the phase transition in type-I clathrates Rb Cs8–Sn44□2 (1.3≤x≤2.1) using single-crystal X-ray diffraction, Raman spectroscopy, heat capacity and electrical resistivity measurements

Kaltzoglou, Andreas; Fässler, Thomas F.; Gold, Christian; Scheidt, Ernst‐Wilhelm; Scherer, Wolfgang; Kume, Tetsuji; Shimizu, Hiroyasu

doi:10.1016/j.jssc.2009.07.034

Cited by 16 publications

(8 citation statements)

References 19 publications

(30 reference statements)

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“…At room temperature, the α-A 8 Sn 44 2 phase adopts the type-I clathrate structure with a 2 × 2 × 2 superstructure (Ia3d space group) of the primitive cubic unit cell (Pm3n), which originates from a partial ordering of defects. The reversible transformation into the high-temperature β-form with the smaller unit cell with primitive symmetry occurs at the temperatures higher than 330 K [35,45,[48][49][50]. However, our SCXRD experiments performed at 200(2) K showed that some datasets could be indexed in Pm3n space group (Table 4), whereas other datasets show super-structure reflections consistent with the Ia3d model.…”

Section: Resultsmentioning

confidence: 73%

“…The initial idea of the synthesis was to incorporate Europium into the clathrate cage as an extension of the work on Rb 8−x Eu x (In,Ge) 46 clathrates performed previously by our group [32], which proved unsuccessful (vide supra). The co-existence of both alkali metals and alkaline-earth metals, or Eu, is known for the different type-I clathrates, such as K 6 AE 2 M 5 Ge 41 (AE = Eu, Ba; M = Zn, Cd) and K 6 Eu 2 Ga 10 Ge 36 [7,33] [44,45], which show the tendency for the larger Cs to fill the larger 24-vertex cages, while the smaller Rb and K, in particular, are better suited for the smaller 20-vertex cage (Figure 2). The report on K 7.1 Ba 0.3 Ga 8.3 Sn 37.7 shows that it is possible to have Sn-bearing clathrates with guest atoms from Groups 1 and 2, where Ba occupies only one (2a) site [24].…”

Section: Resultsmentioning

confidence: 99%

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Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Baranets

Childs

et al. 2020

Crystals

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Exploratory studies in the systems Rb–Ga–Sn and Cs–Ga–Sn yielded the cubic type-I clathrates with refined compositions Rb8GaxSn46−x and Cs8GaxSn46−x (6.9 < x < 7.5). Nearly single-phase materials with good crystallinity were obtained from stoichiometric reactions of the elements. The structures were characterized by means of single-crystal X-ray diffraction methods. Both Rb8GaxSn46−x and Cs8GaxSn46−x represents cases, where a Group 13 element randomly substitutes a Group 14 element in the structure. The extent of Ga/Sn mixing is apparently governed by the drive of the system to achieve an optimal valence electron count, and hence, Rb8GaxSn46−x and Cs8GaxSn46−x (x ≈ 8) can be regarded as Zintl phases. This notion is supported by structure refinements on a multitude of single-crystal X-ray diffraction data, which also confirm that both types of cages in the cubic type-I structure are fully occupied by Rb and Cs atoms. The open-framework, comprised of 46 nodes per formula unit, adapts to the incorporation of nearly eight Ga atoms within the matrix of Sn, whereby small, short-range distortions result. The exact nature of these effects is still unclear, as so far, the structural variations could only be modeled as both positional and occupational disorder at one of three framework sites. Since vacancies in the structures of the binary type-I clathrates A8Sn46−x☐x (A = Rb, Cs; ☐ = missing Sn atom) are also known to cause local distortions, the latter were also synthesized with the same protocols used for the synthesis of A8GaxSn46−x and structurally re-analyzed. The results from the latter studies confirm that homogeneity issues abound, and that the final structures/compositions are an intricate function of the experimental conditions.

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Section: Resultsmentioning

confidence: 73%

Section: Resultsmentioning

confidence: 99%

Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Baranets

Childs

et al. 2020

Crystals

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“…The XRPD patterns were indexed in agreement with the reflection conditions of space group Ia $\bar{3}$ d , which is also supported by the TEM/SAED studies (Figure 3). This space group has already been known for the clathrate‐I phases M 8 Sn 44 □ 2 ( M = Rb, Cs)18–20 or Ba 8 Ge 43 □ 3 ,21–23 for which an ordering of vacancies leads to a 2 a 0 × 2 a 0 × 2 a 0 superstructure. In the case of compositions such as K 8 Li 2.29(16) Ge 43.47(3) □ 0.24(15) , however, the vacancy concentration is only small, so that the superstructure formation should primarily be related to an ordering of lithium atoms.…”

Section: Resultsmentioning

confidence: 91%

Kongresse – Symposien – Seminare – Messen

2016

Beton und Stahlbetonbau

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“…The Zn defects in Zn-Sb compounds and Cu defects Cu defects in Cu-chalcogenides are essential for decreasing lattice thermal conductivity and tuning of carrier concentrations [4][5][6][7][8][9][10]. In some Type-I clathrates, defects have been found in frameworks and the ordering of vacancies are important for the tuning of the Seebeck coefficient, electrical resistivity and thermal conductivity [11][12][13][14][15]. Defects in clathrates can also change the band structure as the bonding and antibonding orbitals of framework elements contribute to the bands near the Fermi-level [11].…”

Section: Introductionmentioning

confidence: 99%

Optimization of Ca14MgSb11 through Chemical Substitutions on Sb Sites: Optimizing Seebeck Coefficient and Resistivity Simultaneously

Lee

Kauzlarich

2018

Crystals

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In thermoelectric materials, chemical substitutions are widely used to optimize thermoelectric properties. The Zintl phase compound, Yb 14 MgSb 11 , has been demonstrated as a promising thermoelectric material at high temperatures. It is iso-structural with Ca 14 AlSb 11 with space group I4 1 /acd. Its iso-structural analog, Ca 14 MgSb 11 , was discovered to be a semiconductor and have vacancies on the Sb(3) sites, although in its nominal composition it can be described as consisting of fourteen Ca 2+ cations with one [MgSb 4 ] 9− tetrahedron, one Sb 3 7− linear anion and four isolated Sb 3− anions (Sb(3) site) in one formula unit. When Sn substitutes Sb in Ca 14 MgSb 11 , optimized Seebeck coefficient and resistivity were achieved simultaneously although the Sn amount is small (<2%). This is difficult to achieve in thermoelectric materials as the Seebeck coefficient and resistivity are inversely related with respect to carrier concentration. Thermal conductivity of Ca 14 MgSb 11-x Sn x remains almost the same as Ca 14 MgSb 11. The calculated zT value of Ca 14 MgSb 10.80 Sn 0.20 reaches 0.49 at 1075 K, which is 53% higher than that of Ca 14 MgSb 11 at the same temperature. The band structure of Ca 14 MgSb 7 Sn 4 is calculated to simulate the effect of Sn substitutions. Compared to the band structure of Ca 14 MgSb 11 , the band gap of Ca 14 MgSb 7 Sn 4 is smaller (0.2 eV) and the Fermi-level shifts into the valence band. The absolute values for density of states (DOS) of Ca 14 MgSb 7 Sn 4 are smaller near the Fermi-level at the top of valence band and 5p-orbitals of Sn contribute most to the valence bands near the Fermi-level.

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Investigation of substitution effects and the phase transition in type-I clathrates Rb Cs8–Sn44□2 (1.3≤x≤2.1) using single-crystal X-ray diffraction, Raman spectroscopy, heat capacity and electrical resistivity measurements

Cited by 16 publications

References 19 publications

Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Complex Disorder in Type-I Clathrates: Synthesis and Structural Characterization of A8GaxSn46−x (A = Rb, Cs; 6.9 < x < 7.5)

Kongresse – Symposien – Seminare – Messen

Optimization of Ca14MgSb11 through Chemical Substitutions on Sb Sites: Optimizing Seebeck Coefficient and Resistivity Simultaneously

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