Li3GaTe4O11: small ion-driven orientation of TeOn units in a tunnel-structured tellurite.

In Li3GaTe4O11, asymmetric TeOn (n = 3, 4) polyhedra and GaO6 octahedra form a three-dimensional (3D) tunnel framework, with Li+ cations occupying the sixteen-membered channels. The high framework density (12.1) and small void space (3.75%) of Li3GaTe4O11 collectively demonstrate that Li+ cations are spatially confined within the tunnels by the dense, compact framework. This confinement amplifies their steric influence, thereby enabling effective regulation of TeOn (n = 3, 4) with large local dipole moments. The real-space projections of the valence band maximum (VBM) and conduction band minimum (CBM) also reveal that small interstitial Li+ cations can act as "structural mediators" to tune the arrangement of TeOn (n = 3, 4) units, thereby influencing the framework of Li3GaTe4O11. This work opens a new avenue for exploring non-centrosymmetric (NCS) materials through resident cation engineering.