Ba 4 M 3 LiO 12 (M Ο Ta, Nb) (4), Ba 5 W 3 Li 2 O 12 (5) or by The new complex perovskite-like oxide Ba 8 Ta 6 NiO 24 was cations and vacancies. The simplest example of a fully synthesized and its crystal structure was studied using X-ray ordered distribution of high charged cations and vacancies powder diffraction, electron diffraction, and high resolution in the chains of FSO is the Ba 5 Ta 4 O 15 crystal structure (6) electron microscopy. The Ba 8 Ta 6 NiO 24 structure is based on a which is based on a (hccch) close packing sequence and 8H (cchc) 2 close-packed stacking of BaO 3 layers (space group contains chains of three face-sharing octahedra. The cation P6 3 cm, a β«Ψβ¬ 10.07458(6) A Λ, c β«Ψβ¬ 19.0122(2) A Λ.). The structural vacancies are located in the central octahedron while the refinement gave the following values of reliability factors: Ta ions are in the others; this leads to the largest distance R F β«Ψβ¬ 0.028, R P β«Ψβ¬ 0.042, R wP β«Ψβ¬ 0.056. The main feature of this between Ta 5Ο© cations. When part of Ta 5Ο© cations are restructure is the existence of two different pairs of face-sharing placed by Ti 4Ο© ions the formation of Ba 10 Ta 7.04 Ti 1.2 O 30 and octahedra. In the first pair one octahedron is occupied by Ta Ba 8 Ta 4 Ti 3 O 24 compounds is possible (7). Their structures whereas the other one is empty. In the second pair one of are based on a 10H (cchcc) 2 and a 8H (cchc) 2 close-packing, the two octahedra is occupied by Ta and a cation vacancy and its neighbor is occupied by Ni, Ta, or a vacancy. This distribu-respectively. The reduction of electrostatic repulsion betion of cations was completely confirmed by electron microstween the two high-charged cations in adjacent octahedra copy. The formation of a Ba 8 Ta 6Ψ0.4x Ni 1Ψx O 24 solid solution with in (chc) lamellae is achieved by the existence of two differa narrow homogeneity range with (Ψ0.2 Υ
x Υ
0.2) was ent types of pairs of FSO. One of them is statistically observed.