High-Entropy Skutterudites as Thermoelectrics: Potential Synthesizability, Enhanced Stability and Band Convergence via the Cocktail Effect

TL;DR

This work screens high-entropy skutterudites for thermoelectric applications using the disordered enthalpy-entropy descriptor (DEED) within a high-throughput density functional theory framework to assess synthesizability and stability. It analyzes nine Fe-containing, 24-electron skutterudites in a 32-atom cell to map configurational thermodynamics and electronic structure, including band-gap reductions and potential band convergence driven by a cocktail effect. The results show high power factors and competitive zT values, aided by reduced lattice thermal conductivity from enhanced phonon scattering and mode overlap, along with improved dynamical and mechanical stability. Collectively, the findings outline a path to durable, cost-effective, high-performance thermoelectrics by exploiting the expansive HE skutterudite chemical space and band-structure engineering.

Abstract

High entropy materials offer a promising avenue for thermoelectric materials discovery, design, and optimization. However, the large chemical spaces that need to be explored hamper their development. In this work, a large family of high-entropy skutterudites is explored as promising thermoelectric materials. Their potential synthesizability is screened and rationalized using the disordered enthalpy-entropy descriptor through high-throughput density functional theory calculations. In the case of high-entropy skutterudites, the thermodynamic density of states and the entropy gain parameter appear to be key factors for their stabilization. Electronic band structure analyses not only show a reduction in the band gap, which enhances carrier concentration and electrical conductivity, but also a band convergence phenomenon for some specific compositions, which is related to the "cocktail effect". Analyzing atom-projected band structures shows how band convergence is due to the simultaneous presence of Fe, Ni, and Co in the compound. The presence of Rh or Ir, while not contributing to this band convergence effect, can be directly linked to an increase in system's entropy, which enhances the thermodynamic stability of these materials. Transport properties are computed for the most promising compositions, and their dynamical, mechanical, and thermal stability are addressed. Our results demonstrates that these types of compounds open new avenues, not only to enhance thermoelectric efficiency but also to reduce costs by utilizing more abundant elements and also improving their durability.

Figures (6)

• Figure 1: Thermodynamic density of states of HE skutterudites studied in this work.
• Figure 2: Band structure and density of states, DOS, for CoSb$_3$ obtained with r$^2$SCAN functional.
• Figure 3: Unfolded band structure and density of states, DOS, for HE skutterudites obtained with r$^2$SCAN functional. Most stable configurations are labeled as GS and the other three most stable configurations as GS+X. Energy difference between configurations and GS is included in parenthesis in meV atom$^{-1}$.
• Figure 4: Atomic projected band structure of (FeNiCoRh)Sb12 and (FeNiRhIr)Sb12.
• Figure 5: a,b) Dispersion curves c,d) vibrational density of states, pDOS, and cumulative lattice thermal conductivity, $\kappa$, e) group velocities, $v$, and f) scattering rates, $W$, for CoSb3 and (FeNiCoRh)Sb12 at 300K.