Modulated structure of Ba6ZnIr4O15; a comparison with Ba6CuIr4O15 and SrMn1-xCoxO3- y

Abstract

The new phase Ba ₆ CuIr ₄ O ₁₅ has been shown by powder X-ray diffraction to be a member of the perovskite-related structural family A _3n+3 A′ _n B _n+3 O _6n+9 withn=1; space group R32, a=10.1196(3), c=13.4097(4) Å. The trigonal-prismatic A′ sites and the octahedral B sites are both occupied by a disordered distribution of Ir and Cu. A combination of electron microscopy and X-ray diffraction has shown that Ba ₆ ZnIr ₄ O ₁₅ has a related incommensurate structure with a≈10.1, c≈4.4 Å and a modulation vector q = a *+0.35 c *. Alternatively, Ba ₆ ZnIr ₄ O ₁₅ can be considered as a composite of trigonal (cell 1) and rhombohedral (cell 2) substructures with a ₁ =a ₂ =10.1228(9) c ₁ =4.4099(6), c ₂ =2.6982(2) Å. It is shown that the same structural formalism can be used to describe the incommensurate hexagonal phase of SrMn _1-x Co _x O _3-y .