First series of transition-metal-layered oxycarbonates:: Sr4Fe2-xMxO6CO3 (M = Sc, Ni, Co)

The possibility of synthesizing layered oxycarbonates, with nominal composition Sr4Fe2-xMxO6CO3 (with M = Sc, Co, or Ni) involving trivalent scandium, cobalt, or nickel, with 0 less than or equal to x less than or equal to 2 (M = Sc), 0 less than or equal to x less than or equal to 1.5 (M = Co), and 0 less than or equal to x less than or equal to 1.1 (M = Ni), is reported for the first time. The structural studies of Sr4Sc2O6CO3 and Sr4FeMO6CO3 (M = Co and Ni) show that these three phases are closely related to the n = 3 member of the Ruddlesden-Popper family. They derive from the latter by replacing the middle layer of transition-metal octahedra by triangular CO3 groups, with two different "flag" and "coat hanger" configurations. Magnetic behaviors that are fundamentally different from the magnetic behavior of Sr4Fe2O6CO3 are also reported.