New KRb2Sb4BO13 and Rb3Sb4BO13 compounds prepared by Rb+/K+ ion exchange from the K3Sb4BO13 ion conductor

Abstract

The crystal structures of new K_3−xRb_xSb₄BO₁₃ compounds (x = 2, 3), prepared via ion exchange from K₃Sb₄BO₁₃, are reported. They adopt the triclinic crystal system and exhibit a localized Rb/K disorder at room temperature. The crystal structures were determined from single-crystal X-ray diffraction at T = 25 °C for both end-members of the family, leading to a reinvestigation of the K₃Sb₄BO₁₃ crystal structure, and one intermediate composition KRb₂Sb₄BO₁₃. The structure consists of hexagonal Sb₃O₉ bronze-like layers alternately separated by edge-sharing Sb₂O₁₀ dimers and BO₃ triangles, forming interconnected tunnels filled by Rb⁺/K⁺ ions. The differences between the structures are based on the Rb/K disorder inside the tunnels conferring an advanced view of the cation diffusion paths. Additional information about conduction pathways was provided by the bond valence energy landscape (BVEL) method.