Type-I clathrate structure

Type I clathrate structures are synthesized from finely divided Si or Ge powder with potassium vapor at 700°C under low pressure . The homologous Sn compound is formed by melting together stoichiometric amounts of potassium and tin. ... 

Table 4.1 Systematic changes in cell parameter ao, the bulk modulus (Kq) and its pressure derivative Kd) with the progressive filling of the nanocages (x = 0, 2, 6 and 8) in the Type I clathrate structure obtained from ab initio calculations (from [78])...

M. Hayashi, K. Kishimoto, K. Akai, H. Asada, K.T. Kishio, K. Koyanagi, Preparation and thermoelectric properties of sintered n-type KgMgSnsg (M = Al, Ga and In) with the type-I clathrate structure. J. Phys. D Appl. Phys. 45, 455308 (2012)... 

Fig. 8.1 A view of the Type I clathrate structure type showing a view of the (a) unit cell down the a axis, (b) the 20 vertex cage and (c) the 24 vertex cage. The large green) spheres are the guest ion and the small (yellow) spheres are the framework atoms...

Fig. 1. Type-I clathrate structure, drown by VESTA3[3] based on data from Ref 2.

Figure 2 shows XRD patterns of bulk surface of BagAlisSisi clathrate (a) before and (b) after the heat treatment in air at 873 K for 240 h. It is found that the major phase of the specimens is the type-I clathrate structure, in agreement with the reference BagAlieSiso (PDF No. 

Fig. 11. Clathrate hydrates (a) basic structural component (H4002o pentagonal dodecahedron) (b) type I host structure (two face-sharing 14-hedra are...

Gas hydrates usually form two crystallographic stmctures - stmcture Type I and structure Type II. Rarely, a third structure may be observed (Type H). Figure 3.1 shows these three stmctures of clathrate hydrates and Table 3.1 presents their stmctural properties. 

Sodium, with a covalent radius of 157 pm, can occupy all the available voids of both structures, but the type II host lattice is the more stable. Experimental data agree with this argument type I clathrates are formed in milder conditions than type II. This type II structure formed with small sodium atoms is unique and has no hydrate equivalent both voids are occupied stoichiometrically and a large range of composition is observed 3 < x < 22. 

The thermal treatment under vacuum in the temperature range 320-400 °C of NaGe led to the formation of a mixture of a type II Na Geisg clathrate and another phase of composition close to NaGe4, occurring essentially at low temperature (320-360 °C), the structure of which was quite different from that of a type I clathrate and not identified so far. The sodium content in the minority phase Na Ge e was not possible to determine acciu ately. 

A remarkable variation of the type-I clathrate superstructure is associated with the formation of semiclathrates in the Ge-P-Q (Q = Se, Te) systems [34, 35]. The term semiclathrate was first introduced for hydrates of quaternary ammonium salts, which show general structural and physical properties of normal clathrates but in addition feature a single hydrogen bond between host and guest substructures [50]. Up to now quite a number of semiclathrates-hydrates have been reported in the literature [51] compared to a very limited number of inorganic semiclathrates, which are exclusively cationic semiclathrates. 

Sii32P4oTe2i,5 is the only type-III cationic clathrate for which the thermal conductivity was measured [52]. It takes the value of 1.5 W m at room temperature and decreases with increasing temperature until a broad maximum of 1 W m is reached at about 600 K it increases slightly with further increase of temperature reaching again 1.5 W m at 1,023 K. Noticeably, the thermal conductivity of the type-III cationic clathrates is significantly lower than for the type-I counterparts (Table 5.2). Two factors can be considered. First, the crystal structure of the type-III clathrate is much more complex than that of the type-I clathrate second, the type-III clathrate is a semiconductor, and the electronic part of the thermal conductivity is low. 

A.P. Wilkinson, C. Lind, R.A. Young, S.D. Shastri, P.L. Lee, G.S. Nolas, Preparation, transport properties, and structure analysis by resonant X-ray scattering of the type I clathrate CsgCd4Sn42. Chem. Mater. 14, 1300-1305 (2002)... 

A. Kaltzoglou, S. Ponou, T.F. Fassler, Synthesis and crystal structure of mercury-substituted type-I clathrates AgHg4Sn42 (A = K, Rb, Cs). Eur. J. Inorg. Chem. 4, 538-542 (2008)... 

T. Tanaka, T. Onimaru, K. Suekuni, S. Mano, H. Fukuoka, S. Yamanaka, T. Takabatake, Interplay between thermoelectric and structural properties of type-I clathrate KgGagSn3g single crystals. Phys. Rev. B 81, 165110 (2010)... 

Y. Saiga, K. Suekuni, B. Dua, T. Takabatake, Thermoelectric properties and structural instability of type-I clathrate BagGai Snso at high temperatures. Solid State Common. 152, 1902-1905 (2012)... 

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