New KRb2Sb4BO13 and Rb3Sb4BO13 compounds prepared by Rb+/K+ ion exchange from the K3Sb4BO13 ion conductor
The crystal structures of new K3−xRbxSb4BO13 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.