Crystal Chemistry of NaSICONs: Ideal Framework, Distortion, and Connection to Properties

The crystal structure of R (3) over barc NaSICON type AxM(2)(TO4)(3) (M = Al, Ce, Co, Cr, Fe, Ge, Hf, In, Li, Mg, Mn, Mo, Na, Nb, Ni, Sb, Sc, Se, Sn, Ta, Ti, U, V, Y, Yb, Zn, Zr; T = As, Ge, Mo, P, S, Si, V) with its multiple internal degrees of freedom offers considerable flexibility and can accommodate dozens of different ions leading to hundreds of reported compositions. In this work, the ideal R (3) over barc structure with undistorted [MO6] octahedra and [TO4] tetrahedra is parametrized and used to quantify distortion of about 340 real NaSICON-type oxides consistently across the entire family. It is shown that distortion is primarily driven by the size mismatch between the A cations and M-2(TO4)(3) framework, that can be used to optimize the geometry of the structure to control properties, such as A-ionic conductivity or thermal expansion.

Automated summary

The study reveals that distortion in NaSICON-type oxides is primarily driven by the size mismatch between A cations and M-2(TO4)(3) framework, which can be utilized to optimize the geometry of the structure to control properties such as A-ionic conductivity or thermal expansion.