Potential thermoelectric material Tl₃XS₄ (X = V, Nb, Ta) with ultralow lattice thermal conductivity

The demand for sustainable energy solutions has driven intensive research into advanced thermoelectric (TE) materials, to harness waste heat for efficient power generation. Recently, several studies have revealed that Tl₃VS₄ possesses an ultralow lattice thermal conductivity, despite its simple body-centered cubic lattice structure. This paper focuses on the TE properties of Tl₃XS₄ (X = V, Nb, Ta) compounds through a systematic exploration utilizing first-principles calculations and semiclassical Boltzmann transport theory. The results of the AIMD simulation and phonon calculation reveal the excellent dynamic stability and thermal stability of Tl₃XS₄ at 300, 500, and 700 K. Moreover, we find that the Tl₃XS₄ compounds present ultralow lattice thermal conductivity (<0.5 W m^-1 K^-1 at 300 K), and the nanostructure strategy is effective. Based on the outstanding Seebeck coefficient and ultralow lattice thermal conductivity, the optimal ZT values of Tl₃VS₄, Tl₃NbS₄, and Tl₃TaS₄ at 300 K are determined to be 1.17 (p-type), 0.84 (n-type), and 0.65 (p-type), respectively. Additionally, at each considered temperature, the maximum ZT values of p-type (n-type) Tl₃XS₄ follow the order: Tl₃VS₄ > Tl₃NbS₄ > Tl₃TaS₄ (Tl₃NbS₄ > Tl₃VS₄ > Tl₃TaS₄). Our results demonstrate that Tl₃XS₄ (X = V, Nb, Ta) compounds are promising thermoelectric materials. This exhaustive research enhanced our nuanced comprehension of the electronic, dynamic, and thermoelectric attributes of Tl₃XS₄ (X = V, Nb, Ta), thereby offering valuable insights into the TE field.