First-principles investigations of defect and phase stabilities in thermoelectric (GeTe)_x(AgSbTe₂)_1−x

Abstract

We focus on the defect and phase stabilities in the pseudo binary alloy (GeTe) x (AgSbTe 2 ) 1%x (TAGS; tellurium antimony germanium silver). TAGS is expected to be a high effective thermoelectric material because its thermal conductivity shows anomalous behavior around the concentration of x = 0.8. The origin of the anomalous thermal conductivity and the stable structure in TAGS have not been well understood. To clarify the stable structure, we calculate the formation energies of the point and complex defects. It is found that the chain structure of Ag-Te-Sb has a lower formation energy in GeTe, and the system becomes more stable by assembling the Ag-Te-Sb chain structures. Moreover, the calculated mixing energy also shows that the TAGS system tends to undergo phase separation. In such structures, the grain boundary plays an important role in inducing large phonon scattering, leading to the thermal conductivity reduction.

Spinodal nanodecomposition in semiconductors doped with transition metals

“…Metallic nanocolumns and nanodots could also serve as high quality nanocontacts in nanoelectronics and optoelectronics as well as metallic elements in nanoplasmonics. Dense arrays of nanocolumns are also attractive for thermoelectric applications (power generators and coolers) as a specific form of density of states in 1D systems is expected to result in a significant enhancement of the Seebeck and Peltier effects (Shinya et al, 2014;Vu et al, 2014aVu et al, , 2015Vu et al, , 2011Vu et al, , 2014b. Furthermore, the growth process presented in Fig.…”

Criteria for extending the operation periods of thermoelectric converters based on IV-VI compounds

“…2b. The possibility for a miscibility gap, in the liquid or solid states, allowing potential phase separation into the nano-scale and potentially reduced lattice thermal conductivity and enhanced ZT [12], shown schematically in the figure, was previously reported for the Pb-Te [36], Sn-Te [37] and TAGS (GeTe) x (AgSbTe 2 ) 1 À x [38] systems.…”

Computational materials design for efficient red luminescence: InGaN codoped with Eu and the donor–acceptor pair of Mg and O

“…[30][31][32][33] A phase diagram of InGaN decomposition was examined in accordance with the methodology described in previous papers. 34,35) The exchange correlation energy was approximated in accordance with the Moruzzi, Janak, and Williams formula. 36) The calculations were done within the semi-relativistic framework.…”

“…When an atom denoted by α is doped to a substitutional site of an atom denoted by β, the formation energy E form (E F ; α) with system charge q is calculated by the minimum of [E α (q; E F )]. 35,40) E F is the Fermi level displacement induced by the doping effect and is measured from the valence band maximum E VBM . The q-dependent total energy for element α, E form (E F ; α), is provided by…”