Computational Investigation of the Thermoelectric Performance of Environmentally Friendly and Earth-Abundant SrZn₂S₂O

Thermoelectric (TE) materials enable direct conversion between heat and electricity, allowing efficient recovery of waste heat, which accounts for nearly 50% of global energy consumption. Therefore, TE materials hold great potential for applications in waste heat recovery and sustainable energy technologies. Owing to the composition of earth-abundant and low-toxicity elements, as well as the presence of relatively heavy elements and mixed-anion characteristics, SrZn₂S₂O is considered a promising, environmentally friendly TE material. In this study, the TE performance of SrZn₂S₂O was investigated based on density functional theory (DFT) and compared with that of the prototypical mixed-anion oxide BiCuSeO. The calculated results show that SrZn₂S₂O exhibits a higher optimal average p-type power factor than that of BiCuSeO at 900 K, reaching 1150 μW m^–1 K^–2 compared with 770 μW m^–1 K^–2 for BiCuSeO. In addition, nanostructuring strategies can reduce the lattice thermal conductivity of SrZn2S2O by 40% or more in all crystallographic directions. This leads to a maximum n-type ZT value of 0.65 along the b direction and a maximum p-type ZT value of 0.77 along the c direction for SrZn₂S₂O.