All nine in (II) or six symmetry-independent alkali metal positions in (I) are mixed occupied by cesium and rubidium. In the case of (I), the coordination numbers vary from 12, 14, 15 to 16 (d(A- A) ≤5.5 Å; d(A-Tl)≤4.51 Å) (see Figure ). They can be differentiated first of all in coordinations with three (A1, A2, A5, A6) and four [Tl6] 6-octahedra (A3, A4). The latter positions also show the highest cesium content (see Table ). In general, the coordination polyhedra are similar to those found in binary KTl and CsTl (see Figure , 5 and, SI chapter 6). The alkali metal positions A1, A5, and A6 are coordinated similarly to Cs3 (Wyckoff 16f) in CsTl. The ternary materials when mixing rubidium and cesium combine structural features of KTl and CsTl. As demonstrated in Figure , the coordination sphere of A2 is analogous to that of K2 (Wyckoff 8d) in KTl and Cs2