# Defect-Energy-Targeted Lattice Repair Delivers High Thermoelectric Performance in Magnesium Antimonide

## TL;DR

This paper introduces a new method to improve the thermoelectric performance of magnesium antimonide by repairing lattice defects, leading to a record efficiency in converting waste heat to electricity.

## Contribution

A defect-energy-targeted lattice repair strategy using alkaline-earth metals to enhance thermoelectric performance in Zintl-phase materials.

## Key findings

- Substituting Mg with Ca, Sr, or Ba increases vacancy formation energy, reducing carrier scattering.
- The approach boosts carrier mobility by 35% while maintaining carrier concentration.
- The resulting material achieves a zT of 2.1 at 773 K and a 14% conversion efficiency in a single-leg device.

## Abstract

Magnesium-based Mg3(Sb,Bi)2 has
emerged as
a premier candidate for waste-heat recovery. However, its performance
is fundamentally capped by intrinsic Mg vacancies that severely scatter
carriers. Here, we overcome this bottleneck via a defect-energy-targeted
lattice repair strategy, substituting labile Mg sites with homologous
alkaline-earth metals (Ca, Sr, Ba). Theoretical calculations reveal
that the lower electronegativity of these dopants strengthens the
local metal–Sb bonding, drastically raising the vacancy formation
energy from ∼0.97 to ∼2.42 eV. This thermodynamic stabilization
effectively “repairs” the lattice, suppressing vacancy
generation and yielding a ∼35% boost in carrier mobility without
compromising carrier concentration. Simultaneously, the heavy dopants
induce mass fluctuations and strain fields that, coupled with dense
dislocations, minimize the lattice thermal conductivity to ∼0.4
W m–1 K–1 at 773 K. The synergy
of restored charge transport and suppressed heat propagation leads
to a record-high figure of merit (zT) of ∼2.1
at 773 K and an outstanding average zT of ∼1.5
in Mg3.2Ba0.005Sb1.5Bi0.49Te0.01. Remarkably, a single-leg device demonstrates a
conversion efficiency of ∼14%, outperforming state-of-the-art
n-type thermoelectrics. This work demonstrates that targeting defect
energetics is a powerful, broadly applicable approach to breaking
the performance ceilings of Zintl-phase thermoelectrics.