Predicting room-temperature conductivity of Na-ion super ionic conductors with the minimal number of easily-accessible descriptors

Given the vast compositional possibilities Na_nM_mM_m'Si_3-p-aP_pAs_aO_12, Na-ion superionic conductors (NASICON) are attractive but complicate for designing materials with enhanced room-temperature Na-ion conductivity σ_ Na,300K. We propose an explicit regression model for σ_ Na,300K with easily-accessible descriptors, by exploiting density functional theory molecular dynamics (DFT-MD). Initially, we demonstrate that two primary descriptors, the bottleneck width along Na-ion diffusion paths d_1 and the average Na-Na distance ⟨ d_ Na-Na⟩, modulate room-temperature Na-ion self-diffusion coefficient D_ Na,300K. Then, we introduce two secondary easily-accessible descriptors: Na-ion content n, which influences d_1, ⟨ d_ Na-Na⟩, and Na-ion density ρ_ Na; and the average ionic radius ⟨ r_M ⟩ of metal ions, which impacts d_1 and ⟨ d_ Na-Na⟩. These secondary descriptors enable the development of a regression model for σ_ Na,300K with n and ⟨ r_M ⟩ only. Subsequently, this model identifies a promising yet unexplored stable composition, Na_2.75Zr_1.75Nb_0.25Si_2PO_12, which, upon DFT-MD calculations, indeed exhibits σ_ Na,300K > 10^^3 S·cm^-1. Furthermore, the adjusted version effectively fits 140 experimental values with R^2=0.718.