Chemical trends of the band gaps of idealized crystal of semiconducting silicon clathrates, M8Si38A8 (M = Na, K, Rb, Cs; A = Ga, Al, In), predicted by first-principle pseudopotential calculations

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

“…Actually, calculated band gaps were 0.98, 1.53, 0.76, 0.80, 0.82, 0.88, 0.91 and 0.97 eV for the diamond Si, Si 46 38 , respectively, at the EV-GGA level. Although a systematic difference was found between the present band gaps and those obtained by Imai et al 15) using different functional, the present band gaps are consistent with those in the previous theoretical work. The order of carrier densities where the Seebeck coefficient reaches a maximum is consistent with the previously mentioned order of band gaps for each composition.…”

“…In addition, as shown in next section, it was found that the effect of different configurations of the substitutional atom on the thermoelectric properties was negligible. Moreover, the lowest energy configuration obtained in the present study is more stable than the one calculated by Imai et al 15) by 0.21 eV/f.u., where the previous experimentally determined occupancy 37,40) was used. On the basis of the above result for the stable configurations of substitutional atoms, the formation energies of X 8 Y 8 Si 38 per chemical formula were calculated and are shown in Fig.…”

“…41) They suggested that the discrepancy between the observed band gap and their calculated one (0.798 eV 15) ) may be due to random substitutional positioning of Ga, vacancies, nonstoichiometry, and so on. It can be considered that random Ga configuration does not significantly narrow the band gap because the change in the band gap was found to be at most 0.1 eV, as demonstrated by changing the Ga configuration in the present work.…”

“…Alkali metals were considered as guest elements because thermoelectric properties in alkali metal encapsulated Si clathrates have not been revealed although their electronic structures were investigated. 15) Reducing the number of substitutional elements is expected to reduce the amount of alloy scattering of the carriers more than using alkali earth elements for the guest elements would. On the basis of the calculated thermoelectric properties, we will discuss the optimal composition of guest and substitutional atoms that maximizes ZT and whether ZT > 1 can be achieved for Si clathrate.…”

A Comparative Study of the Effect of Strain on the Electronic and Optical Properties of Filled and Unfilled Ba8Si46 Type I-clathrate

“…The type-I structure is the most investigated among the different known types, on the other hand, it has an excellent thermoelectric [1], semiconducting, and superconducting properties [2]. Guest free type-I Si 46 silicon clathrate is a hypothetical structure, which has been theoretically studied and expected to exhibit interesting thermoelectric and electronic properties as a promising semiconductor material with a band-gap greater than that of silicon in the diamond structure [3]. However, the actual synthesis of type-I Si 46 clathrate remains a challenging task and yet not resolved.…”