Modulated structure ofBa6ZnIr4O15; a comparison withBa6CuIr4O15 andSrMn1-xCoxO3-y
ABSTRACT The new phase Ba6CuIr4O15 has been shown by powder X-ray diffraction to be a member of the perovskite-related structural family A3n+3A'nBn+3O6n+9 with n=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 Ba6ZnIr4O15 has a related incommensurate structure with a≈10.1, c≈4.4 Å and a modulation vector q=a*+0.35c*. Alternatively, Ba6ZnIr4O15 can be considered as a composite of trigonal (cell 1) and rhombohedral (cell 2) substructures with a1=a2=10.1228(9) c1=4.4099(6), c2=2.6982(2) Å. It is shown that the same structural formalism can be used to describe the incommensurate hexagonal phase of SrMn1−xCoxO3−y.
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ABSTRACT: The new phases (Ba 0.5Sr 0.5) 7Co 6O 18, Ba 8Co 7O 21, and Ba 9Co 8O 12have been shown by electron diffraction and high-resolution electron microscopy to be three new members ( n=5, n=6, and n=7) of the 2H hexagonal perovskite-related An+2 B' BnO 3 n+3 homologous series. Their modulated structures are made up of chains, running along the cdirection and separated by Ba(Sr) ions, containing a succession of one Co atom in prismatic trigonal sites and nCo atoms in octahedral coordination sharing faces. The strategy to synthesize different terms of this family is discussed in terms of the distance between AO 3layers.Journal of Solid State Chemistry 02/1999; 142(2):419-427. · 2.20 Impact Factor
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ABSTRACT: The systematic search of new intermediate phases between 2H-BaCoO 3 and Ca 3Co 2O 6 structures has shown, for the first time, the existence of polymorphism in monodimensional phases of the homologous series ( A3B2O 6) α( A3B3O 9) β. A new Ba 8Co 7O 21 phase, different from the trigonal phase previously reported, has been synthesized. The new material is orthorhombic (SG Fd2 d) with unit cell parameters ao=1.14, bo=1.98, and co=1.75 nm. Both orthorhombic and trigonal phases are built up of isolated rows of polyhedra parallel to the c-axis formed by one trigonal prism and six ocathedra sharing faces, but with a different spatial arrengement between the chains. The orthorhombic structure can be derived from a hcp stacking of Ba 8O 24 and Ba 8Co 2O 18 layers.Journal of Solid State Chemistry 04/2000; 151(1):77-84. · 2.20 Impact Factor
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ABSTRACT: The structure of Ba1+xA′xB1−xO3 (x=0.2124, A′=Ni, B=0.51Ni+0.49Pt) has been solved in the superspace formalism with occupational Crenel functions and sawtooth displacive modulations along the trigonal axis. The structure is described as an incommensurate modulated columnar composite with two subsystems, [(Ni,Pt)O3] and [Ba], respectively. The superspace group is Rm(00γ)0s with a=9.9357(1) Å, c=2.5871(1) Å and q=0.6062c* (Z=3). The structural modulation has two variable parameters: the modulation wave vector or misfit parameter, which is fixed by the composition, and the mismatch between the sizes of the octahedral and prismatic oxygen polyhedra formed in the structure. The model, although developed within the superspace formalism, is closely related to the previously reported polytype layer picture in direct space. This structure is an example of so-called composition flexible systems. The present structural analysis constitutes a merely demonstrates the efficiency of the four-dimensional superspace formalism for describing such phases.International Journal of Inorganic Materials 02/2000; 2(1):71–79.