Excellent Thermoelectric Performance of Bi₂MO₄Cl (M = Y, La, and Bi) Derived from Ultra-Low Lattice Thermal Conductivity Due to Weak Ionic Bonding

Oxides are considered potential candidates for thermoelectric materials due to their high temperature stability in air, low toxicity, and ease of synthesis.¹ However, the thermoelectric figure of merit (ZT) of discovered oxides is still significantly lower compared to conventional thermoelectric materials such as Bi₂Te₃ and PbTe. In this work, we predicted the thermoelectric performance of visible light photocatalysts Bi₂MO₄Cl (M = Y, La, and Bi)² by first-principles calculations based on density functional theory (DFT). The results show that Bi₃O₄Cl and Bi₂LaO₄Cl exhibit ultra-low average lattice thermal conductivities of less than 0.3 W m^-1 K^-1 at 1000 K, which is mainly attributed to the presence of heavy atoms, weak ionic bonding, and strong phonon anharmonicity. In addition, the weak ionic bonding significantly inhibits out-of-plane heat transfer, resulting in the lattice thermal conductivity in the out-of-plane direction being the lowest compared to other directions. As a result, the p-type maximum average ZT of Bi₃O₄Cl reaches 2.2 at 1000 K, which is comparable to that of polycrystalline SnSe,³ and the p-type maximum ZT of Bi₂LaO₄Cl exceeds 4 in the out-of-plane direction. These results not only illustrate the intrinsic mechanism for the excellent thermoelectric performance of Bi₂MO₄Cl (M = Y, La, and Bi), but also provide theoretical insights for further experimental exploration.

References
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