The An+2BnB′O3n+3 family (B=B′=Co):: Ordered intergrowth between 2H-BaCoO3 and Ca3Co2O6 structures

The n integer members of the A(n+2)B(n)B'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 = infinity) 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)(6)Co5O15 (n = 4), Sr5Co4O12 (n = 3), and (Sr0.5Ca0.5)(4)Co3O9 (n = 2). (C) 1999 Academic Press.