Probing the physical properties of novel lead-free double perovskites A2NaAsCl6 (A = K and Rb): a first-principles approach

Renewable energy applications have been explored for A₂NaAsCl₆ (A = K and Rb) owing to its structural, opto-electronic, and thermoelectric properties. The tolerance factor, positive cohesive energy, and formation energy all promise the stability of the compound. Structural parameters show that the atomic radius of Rb is greater than that of K, and hence, the lattice constant increases from K to Rb. With an optimised lattice constant, the band gap values for K₂NaAsCl₆ and Rb₂NaAsCl₆ are 3.522 eV and 3.473 eV, respectively. Therefore, these materials are frequently utilised in solar cell and optoelectronic applications. Thermoelectric and thermodynamic properties are analysed by various parameters. The PF values at 300 K are 1.72 × 10¹¹ W K⁻² ms⁻¹ and 1.67 × 10¹¹ W K⁻² ms⁻¹ for K₂NaAsCl₆ and Rb₂NaAsCl₆, respectively. ZT values of 0.11 and 0.12 demonstrate how important they are for thermoelectric applications at room temperature. These results highlight that further exploration of A₂NaAsCl₆ (A = K and Rb) may enhance the thermoelectric capabilities of K₂NaAsCl₆ and Rb₂NaAsCl₆, making them promising candidates for thermoelectric device applications.