Impact of the scattering physics on the power factor of complex thermoelectric materials

Abstract

We assess the impact of the scattering physics assumptions on the thermoelectric properties of five Co-based p-type half-Heusler alloys by considering full energy-dependent scattering times, versus the commonly employed constant scattering time. For this, we employ DFT bandstructures and a full numerical scheme that uses Fermi's Golden Rule to extract the momentum relaxation times of each state at every energy, momentum, and band. We consider electron-phonon scattering (acoustic and optical), as well as ionized impurity scattering, and evaluate the qualitative and quantitative differences in the power factors of the materials compared to the case where the constant scattering time is employed. We show that the thermoelectric power factors extracted from the two different methods differ in terms of: i) their ranking between materials, ii) the carrier density where the peak power factor appears, and iii) their trends with temperature. We further show that the constant relaxation time approximation smoothens out the richness in the bandstructure features, thus limiting the possibilities of exploring this richness for material design and optimization. These details are more properly captured under full energy/momentum-dependent scattering time considerations. Finally, by mapping the conductivities extracted within the two schemes, we provide appropriate density-dependent constant relaxation times that could be employed as a fast first-order approximation for extracting charge transport properties in the half-Heuslers we consider.

Composition Tuning of Nanostructured Binary Copper Selenides through Rapid Chemical Synthesis and Their Thermoelectric Property Evaluation

“…The Cu 2 Se sample exhibited the highest S value, followed by Cu 1.8 Se. Scattering mechanism, carrier density, density of states near the Fermi level, and band structure play important roles in enhancement of S [ 55 ]. The room temperature Seebeck coefficient value of Cu 2 Se is 60 µV/K and increases to about 220 µV/K, which is roughly 10% greater than values reported by Gahtori et al [ 21 ] (≈ 200 µV/K) and slightly lower than that reported by Yu et al [ 56 ] (≈ 255 µV/K).…”

Efficient calculation of carrier scattering rates from first principles

“…However, in most cases, experimental measurements will not be available and thus this approach cannot easily be applied to new or uncharacterized systems. One alternative is to linearly scale the constant lifetime by the temperature according to τ T ¼ τ 300 T 68 . As demonstrated in Supplementary Figure 9, this results in a considerable improvement in the temperature dependence of mobility, reducing the mean squared error from 3.2 to 0.9.…”

Thermoelectric Properties of InA Nanowires from Full-Band Atomistic Simulations

“…We perform all simulations in this work at room temperature, T = 300 K, and we consider electron-phonon scattering and surface roughness scattering (SRS). It is important to stress that this approach allows for the full energy/momentum dependence of the relaxation times, which is very important in evaluating the TE material properties [47], but are routinely omitted due to the computational burden that it involves. The calculation of the relaxation times depends on the particular scattering mechanism under consideration, and formal treatment of electron-phonon scattering can be found in Ref.…”