Empirical potential description of energetics and thermodynamic properties in expanded-volume silicon clathrates

Chemical aspects of the design of thermoelectric materials

“…It substantially depends on the chemical identity of atoms that form the compound. 93,94 Clathrates described by the Zintl scheme are narrow-gap semiconductors; moreover, the vacancies predicted by this scheme play an important role because the main contribution to the states in vicinity to the Fermi level is made by the orbitals of vacancyadjoining three-coordinated atoms with a lone pair or by the orbitals of heteroatoms. 90,95 By regulating the concentration of vacancies and performing different substitutions in the clathrate framework, it is possible to vary the density of states near the Fermi level, which is reflected in the local electronic environment of atoms and, for tin-based clathrates, was confirmed by MoÈ ssbauer spectra.…”

Crystal-liquid interfaces and phase relations in stable and metastable silicon at positive and negative pressure

“…Guest species are encapsulated into these polyhedra resulting in the formula M 8 Si 46 for fully occupied type I clathrates, where M is typically a group I or II element. Frameworks of type II are made up of pentagonal dodecahedra and 28 atom hexakaidecahedra, with 16 and 8 of these per formula unit, resulting in a stoichiometry of M 24 Si 136 for fully occupied structures.…”

“…22,23 All three of these potentials have been applied to the Si-I and Si 136 structures while the Tersoff and EDIP models have also been applied to Si 46 . 23,24 All reproduce the lattice constants and relative stabilities when compared to experiment and ab initio data, and the SW and EDIP reproduce the observed melting points ͑with the Tersoff potential displaying significantly higher values 24,25 ͒. Molecular-dynamics simulation, 24 conducted with the Tersoff potential, indicates that both Si 136 and Si 46 may be grown through liquid-or solid-phase epitaxy ͑at the crystal/liquid or crystal/amorphous interfaces, respec-tively͒ at temperatures below the ambient pressure Si-I melting point.…”

“…23,24 All reproduce the lattice constants and relative stabilities when compared to experiment and ab initio data, and the SW and EDIP reproduce the observed melting points ͑with the Tersoff potential displaying significantly higher values 24,25 ͒. Molecular-dynamics simulation, 24 conducted with the Tersoff potential, indicates that both Si 136 and Si 46 may be grown through liquid-or solid-phase epitaxy ͑at the crystal/liquid or crystal/amorphous interfaces, respec-tively͒ at temperatures below the ambient pressure Si-I melting point. In addition, the melting relations of the guest-free type II clathrate at both positive and negative pressures have been investigated using the SW potential.…”

Sur les phases de type clathrate du silicium et des éléments apparentés (C, Ge, Sn) : Une approche historique

“…L'évolution observée indique une possible transition de phase vers 27,8 GPa. Dans un autre calcul des propriétés énergétiques et thermodynamiques des clathrates Si 34 et Si 46 par la méthode du potentiel de Terzoff, Morigushi et al ont également déterminé les courbes de dispersion et les densités d'états de phonons des clathrates concernés[144]. Les fréquences actives en Raman calculées sont proches de celles des auteurs antérieurs, avec un maximum situé à 515 cm À1 .…”