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Shanmugasundaram et al. Energy Mater. 2025, 5, 500100 https://dx.doi.org/10.20517/energymater.2024.304 Page 17 of 23

Scheme 1. (A) Phonon scattering in perfect crystal (B) defect structure.

Scheme 2. (A and B) phonon scattering at low and high temperatures.

convergence of multi-band improves the mobility of holes and increases the σ. Therefore, the significant
enhancement of S and σ enhances the overall PF and TE performance.

In this investigation, the Ag-substituted Mg ZnSb compound exhibits the band convergence of heavy VBs Γ
2
2
and lighter VB A near E of the band structure. Benefiting from the improvement of PF and the significant
F
reduction in κ , the Ag-substituted Mg Zn Sb samples show considerably increased zT at the entire
1.8
L
2
1.2
temperature range. The sample Ag Mg Zn Sb shows a peak zT of 0.5 at 753 K, which is ~285%
0.03
1.2
2
1.77
compared to undoped Mg Zn Sb (zT = 0.13). This suggests that heavy element substitution is an effective
1.2
2
1.8
strategy for enhancing the TE transport properties of p-type Mg Zn Sb -based solid solution. Figure 8D
2
1.2
1.8
illustrates the comparison graph of a zT values with reported works. This work suggests that the substitution
of Ag via multiple scattering strategies leads to synergistic enhancement in the TE performance of
Mg Sb -based compounds. Compared with reported single and co-doped Mg Sb -based compounds, this
3
3
3
3
work achieved the highest zT of ~0.5 at 753 K for Ag Mg Zn Sb . Furthermore, the present work has
1.2
2
1.77
0.03
been compared with previous findings in terms of PF, κ , and zT as shown in Supplementary Table 4 [37,45,73-78] .
L
This indicates that Ag substitution at Mg site of Mg Zn Sb -based compounds exhibits enhanced carrier
1.8
1.2
2
and decreased phonon transport properties.