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Shanmugasundaram et al. Energy Mater. 2025, 5, 500100 https://dx.doi.org/10.20517/energymater.2024.304 Page 9 of 23

Figure 3. Temperature dependence of (A) electrical conductivity; (B) Seebeck coefficient; (C) Fermi energy; and (D) S vs. σ for
Ag Mg 1.8-x Zn Sb (x = 0, 0.01, 0.03 and 0.05) samples.
1.2
x
2
minority charge carriers, secondary Sb, and interstitial Ag atoms, which play a major role at high
[56]
temperatures . Therefore, orbital overlap and the strengthening of chemical bond covalency and smaller
electronegativity of Ag atom results in an enhanced DOS m* via VB convergence, which helps to enhance
the S at high temperatures. This finding emphasizes that, the bipolar diffusion effect is possible when VB
electrons are thermally excited to the conduction band (CB) even at relatively lower temperatures .
[57]

Consequently, the peak of S shifts to lower temperatures while the σ continuously increases with Ag
concentration. Also, the Ag Mg Zn Sb shows a drastic improvement in the S of 283 µV/K at 553 K and
1.2
1.79
0.01
2
257 µV/K at 753 K; it might be due to the enhancement of VB convergence, which exhibits a narrow band
gap and lowers the energy separation. This increases the S at high temperatures by enhancing the electronic
[58]
DOS and inhibiting bipolar conduction . Therefore, the introduction of VB convergence is a significant
advantage in improving the S and TE performance over a broad temperature range. This indicates that, the
interstitial silver (Ag) atoms, minority charge carriers, and secondary Sb have significant impacts at high