Regular ArticleThe An+2BnB′O3n+3 Family (B=B′=Co): Ordered Intergrowth between 2H–BaCoO3 and Ca3Co2O6 Structures

The n integer members of the An+2BnB′O3n+3 homologous series keeping B=B′=Co the same have been characterized by selected area electron diffraction and high resolution electron microscopy. Its commensurate modulated structure is made up of chains, separated by A atoms, running along the c direction containing a succession of one Co atom (B′) in prismatic trigonal sites and n Co atoms octahedrally coordinated sharing faces. All of them can be described as ordered intergrowths of two structures of the end members of the family, 2H–BaCoO3 (n=∞) and Ca3Co2O6 (n=1). The modulation observed in all terms can be described as a function of the difference between the c-axis of the Co sublattice with respect to the 2H structure. Members of the series can be obtained by modifying the distance between layers keeping B=Co the same, as shown in (Sr1−xBax)6Co5O15 (n=4), Sr5Co4O12 (n=3), and (Sr0.5Ca0.5)4Co3O9 (n=2).