2 research outputs found
Prediction of New Stable Compounds and Promising Thermoelectrics in the Cu–Sb–Se System
We study the phase stability and
predict as-yet-unreported compounds
in the thermoelectric Cu–Sb–Se ternary system. We use
a combination of total energies obtained from density-functional-theory-based
(DFT) calculations with vibrational entropies from phonon calculations
(within the harmonic approximation) and configurational entropies,
treated with cluster expansions (CE). The Cu–Sb–Se ternary
phase diagram is determined (treating all phases as line compounds)
using the grand-canonical linear programming method. We find the following
results: (1) we predict the stability of a new previously unknown,
zinc blende-based Cu<sub>4</sub>SbSe<sub>5</sub> compound but find
that it is thermodynamically stable up to only ∼300 K; (2)
we also predict that a Cu<sub>12</sub>Sb<sub>4</sub>Se<sub>13</sub> phase (isostructural with Cu<sub>12</sub>Sb<sub>4</sub>S<sub>13</sub>, but unreported in the Cu–Sb–Se system) appears in
the phase diagram at high temperatures (but below the temperatures
where the observed Cu<sub>3</sub>SbSe<sub>3</sub> phase is stable);
(3) based on quasi-harmonic phonon and band structure calculations,
we find that Cu<sub>12</sub>Sb<sub>4</sub>Se<sub>13</sub> has thermal
conductivity and an electronic structure that suggests it as a promising
thermoelectric material
Bi<sub>2</sub>PdO<sub>4</sub>: A Promising Thermoelectric Oxide with High Power Factor and Low Lattice Thermal Conductivity
The search for new energy harvesting
materials that directly convert
(waste) heat into electricity has received increasing attention. Transition
metal oxides are a promising class of thermoelectric (TE) materials
that can operate at high temperature due to their chemical and thermal
stability. However, the high lattice thermal conductivity, poor electrical
conductivity, and low thermopower have significantly impeded their
applications to date. Using first-principles calculations, we predict
a known oxide Bi<sub>2</sub>PdO<sub>4</sub> to be a highly efficient
hole-doped TE material with low lattice thermal conductivity and high
power factor. These properties are due to (i) the strong anharmonicity
stemming from Bi<sup>3+</sup> 6s<sup>2</sup> lone pair electrons (leading
to low lattice thermal conductivity) and (ii) the flat-and-dispersive
valence band structure with high band degeneracy originating from
the localized Pd<sup>2+</sup> <i>d</i><sub><i>z</i><sup>2</sup></sub> orbitals in the stacked square planar ligand field
(leading to a large power factor). Our results highlight the possibility
of oxides as potential TE materials and also afford a novel strategy
of designing TE materials by synthesizing compounds which combine
a lone pair active cation with a <i>d</i><sup>8</sup> cation
in a stacked square planar ligand field