Status: Proposed composition family; DFT and synthesis unverified Date: 2026‑09‑24

Overview

Sr₃Sb₂ is a Zintl-type intermetallic with potential for mid‑temperature thermoelectric applications. The proposed Pb/Si co‑doping strategy aims to simultaneously tune electronic structure, carrier concentration, and lattice thermal conductivity.

1. Host System: Sr–Sb Zintl Phases

Known Sr–Sb phases include SrSb₂, Sr₂Sb₃, Sr₁₁Sb₁₀, Sr₁₆Sb₁₁, Sr₅Sb₃, and Sr₂Sb. Mixing enthalpy is strongly exothermic (≈ –70 kJ/mol). Sr₃Sb₂ is selected as the parent structure due to its electron‑precise bonding and low lattice thermal conductivity typical of Zintl frameworks.

2. Design Target

Thermoelectric figure of merit:

Goal: optimize carrier concentration (~10¹⁹–10²¹ cm⁻³) while minimizing lattice thermal conductivity.

3. Proposed Composition Family

Pb on Sr site (Pb²⁺ → Sr²⁺)

• Potential 6s lone‑pair band convergence near VBM → increased Seebeck coefficient.
• Strong mass contrast → enhanced phonon scattering.
• Electronic effect orthogonal to Si doping.

Si on Sb site (Si⁴⁻ → Sb⁵⁻)

• Aliovalent acceptor doping → controlled p‑type carrier concentration.
• More thermally stable than alkali dopants.
• Solubility and secondary‑phase formation (e.g., SrSi₂) must be evaluated.

4. Dopant Evaluation Summary

• Li (Sr site): strong acceptor; diffusion risk.
• Bi (Sb site): isovalent alloying; reduces κ.
• Pb (Sr site): highest band‑engineering potential; toxicity and phase stability concerns.
• Yb (filler): unlikely due to dense Sr₃Sb₂ lattice.
• Rb/Cs: destabilize lattice; mobile at operating temperatures.
• Tc: impractical.
• SiO₂: detrimental to σ.
• Si (Sb site): promising but untested; solubility unknown.

5. Key Risks / Open Questions

1. Pb 6s band position: must be confirmed by DFT; lone pair may be too deep.
2. Si solubility: risk of SrSi₂ or metallic secondary phases.
3. Zintl electron count: avoid metallization; maintain Fermi level near mobility edge.
4. Sparse literature: limited transport data for doped Sr₃Sb₂.

6. Synthesis Plan

• Arc‑melt elements under inert atmosphere.
• Seal in Ta tube; anneal.
• Ball‑mill to reduce grain size.
• Spark plasma sintering (SPS) to achieve dense, fine‑grained microstructure.
• Multi‑scale phonon scattering via point defects, strain fields, and grain boundaries.

7. Next Steps

• DFT band structure of Pb‑doped Sr₃Sb₂ (Pnma).
• Formation energy and phase stability calculations for Si substitution.
• Literature search for AE₃Sb₂ thermoelectric data.
• Pilot synthesis: x=0.2,  y=0.05 if DFT favorable.