Enhanced Thermoelectric Performance of Polycrystalline Si0.8Ge0.2 Alloys through the Addition of Nanoscale Porosity

Abstract

Engineering materials to include nanoscale porosity or other nanoscale structures has become a well-established strategy for enhancing the thermoelectric performance of dielectrics. However, the approach is only considered beneficial for materials where the intrinsic phonon mean-free path is much longer than that of the charge carriers. As such, the approach would not be expected to provide significant performance gains in polycrystalline semiconducting alloys, such as SixGe1-x, where mass disorder and grains provide strong phonon scattering. In this manuscript, we demonstrate that the addition of nanoscale porosity to even ultrafine-grained Si0.8Ge0.2 may be worthwhile. The semiclassical Boltzmann transport equation was used to model electrical and phonon transport in polycrystalline Si0.8Ge0.2 containing prismatic pores perpendicular to the transport current. The models are free of tuning parameters and were validated against experimental data. The models reveal that a combination of pores and grain boundaries suppresses phonon conductivity to a magnitude comparable with the electronic thermal conductivity. In this regime, ZT can be further enhanced by reducing carrier concentration to the electrical and electronic thermal conductivity and simultaneously increasing thermopower. Although increases in ZT are modest, the optimal carrier concentration is significantly lowered, meaning semiconductors need not be so strongly supersaturated with dopants.

Antibonding or Nonbonding Interaction-Driven Phonon Modes Softening and Wave-like Interband Thermal Conduction in Layered In4Te3 under the Framework of Wigner Transport Formalism

“…Both indium chalcogenides and metal halides are ductile in nature, whereas SnSe is brittle as observed from its values of ξ. Calculated sound velocities of the heat carrying acoustic branch of phonon, Debye temperature, Young’s modulus, and shear modulus are significantly lower in In 4 (Te/Se) 3 than those of the established TE materials, such as Si 0.8 Ge 0.2 (∼5572 m s –1 ) and Mg 2 (Si/Ge/Sn) (∼7300, 6400, 4300 m s –1 ), and comparable to the other state-of-the-art TE materials, such as CuBiI 4 (1487 m s –1 ), Cs 3 Bi 2 I 9 (1297 m s –1 ), Cu 2 Se (1581 m s –1 ), and Bi 2 Te 3 (1761 m s –1 ) . Low sound velocity corresponds to weak In–Te interatomic bonding and eventually leads to low κ L as κ L ∝ v av 3 .…”

Synthesis of Ultrathin AuPt Alloy Porous Nanowires with Abundant Electrocatalytic Active Sites for Excellent Electrocatalysts

“…Based on the Vienna Ab initio Simulation Package (VASP), − generalized gradient approximation of Perdew–Burke–Ernzerhof functions were employed to carry out density functional theory (DFT) calculations. , To describe the interactions between ion cores and valence electrons, the projector augmented wave method was adopted, and the Kohn–Sham equations were expanded in a plane wave basis set with a cutoff energy of 400 eV. Brillouin zone sampling was performed by using a Monkhorst–Pack k -point grid . According to the XRD data, the (111) surface was chosen for investigating the activity of Pt metal and AuPt alloy catalysts.…”

Potential of Recycled Silicon and Silicon-Based Thermoelectrics for Power Generation

“…The ratio of Si to Ge was studied for optimal composition to maximize the scattering of acoustic phonons, and it was found that a 20% substitution of Ge exhibited a significant decrease in thermal conductivity to ~9 W cm −1 K, and a further addition of Ge contributed insignificantly [138]. Additionally, Ge is about 100 times more costly as compared with Si [139]. Therefore, minimizing the required amount for substitution would be financially beneficial.…”