Energetic Stability and Thermoelectric Property of Alkali-Metal-Encapsulated Type-I Silicon-Clathrate from First-Principles Calculation

Abstract

Possible combinations of alkali metal guest atoms and substitutional group-13 atoms in type-I Si clathrate and their thermoelectric properties were investigated using first-principles calculations. All alkali metals could be encapsulated as the guest element into a Si 46 cage, and either Al or Ga was suitable for a substitutional atom. From the formation energy, possible clathrate compositions were selected as K 8 38 . The thermoelectric properties of these compositions were calculated as functions of temperature and carrier density, using the Boltzmann transport equation and the calculated band energy. The obtained dependences of the Seebeck coefficient and electrical conductivity on the carrier density were discussed from the viewpoint of band structure. The thermoelectric properties were optimized to maximize ZT for each composition by controlling the carrier density. ZT µ 0.75 was predicted as the highest ZT value for hole-doped Cs 8 Ga 8 Si 38 .

Si‐based Clathrates with Partial Substitution by Zn and Ga: K8Zn3.5Si42.5, Rb7.9Zn3.6Si42.4, and Cs8–xGa8–ySi38+y

“…Changing the carrier concentration by tuning the electronic structure through element substitution could increase the Figure of merit for A 8 Al 8 Si 38 clathrates significantly. Theoretical calculations performed by Nakamura et al for A 8 Tr 8 Tt 38 clathrates showed that the Figure of merit for optimally doped compounds can reach 0.5 already at 600 K, and for hole‐doped Cs 8 Ga 8 Si 38 even a ZT value of 0.75 at 900 K can be achieved 11. Comparably high values were also calculated by Karttunen et al for alkali‐metal E III / E IV clathrate‐II compounds 12…”

Synthesis, Structure, Thermoelectric Properties, and Band Gaps of Alkali Metal Containing Type I Clathrates: A8Ga8Si38 (A = K, Rb, Cs) and K8Al8Si38

“…26 According to this work the impact of guest atoms on the band gap should be minimal. The effect of the framework cations on the electronic structure is much stronger, 26 which explains the observed narrowing of the band gap (1.40 to 1.18 eV) (see Table 3) upon replacing Al with Ga atoms. Based on the negative sign of the photovoltage, all compounds behave as n-type semiconductors.…”

Mechanical properties of APbX3 (A = Cs or CH3NH3; X= I or Br) perovskite single crystals

“…E and K are Young's and bulk moduli, respectively. The average bond distance refers to structures at room temperature with the mentioned space-groups.An interesting similarity to HaPs in sense of their crystal structure (cubic) and surprisingly low thermal conductivity30,31 , can be found in a structural family called clathrates. Inorganic clathrate compounds (e.g., K 8 Al 8 Si 36 , Sr 8 Ga 16 Ge 30 ) are characterized by an open framework structure with 'guest' ions (e.g.…”