Single crystals of two new barium rhodates were grown from a molten potassium carbonate flux. The new rhodates, Ba(11)Rh(10)O(30) and Ba(32)Rh(29)O(87), are structurally related to the 2H-hexagonal perovskite structure and are characterized by pseudo one-dimensional chains of alternating face-sharing trigonal prisms and octahedra. The structures of Ba(11)Rh(10)O(30) and Ba(32)Rh(29)O(87) were solved using the 4D superspace group approach in Jana2000. Ba(11)Rh(10)O(30), with a repeat of nine RhO(6) octahedra followed by one RhO(6) trigonal prism, contains the longest chain sequence of face-sharing octahedra known for this 2H-perovskite related family of oxides. A structural analysis of these two compounds revealed clear trends in metal-metal distances and octahedral heights not previously identified for this family of oxides. The application of these trends toward the structure of the all-octahedra-containing end member of the structural series, the hypothetical 2H-BaRhO(3), enabled a prediction of its rhodium-rhodium distance, octahedral height, and lattice parameters.

The structures of the trigonal compounds A(1+x)A(x)'B1-xO3 are described, to a first approximation, as a hexagonal close-packed stacking of A(3)O(9) and A(3)A'O-6 layers. However, quantitative analyses are usually performed in superspace, with the structures considered as modulated composites made of two subsystems: chains of A cations, and columns of trigonal prisms, A'O-6, and octahedra, BO6. It is demonstrated that an alternative superspace description as a single modulated structure can be found in terms of the aforementioned layers, with a composition-dependent modulation parameter and discontinuous atomic domains. In this approach, these compounds fulfill layer-stacking rules analogous to those observed in other layered compounds. These rules translate into a so-called closeness condition for the discontinuous atomic domains in superspace; this condition is analogous to that postulated in quasicrystals. Both superspace models, the composite and the layered model, when considered without displacive modulations, can be taken as two limiting idealized paradigms and can be used as the starting point of a structure refinement. As an example, the structure of the trigonal phase Sr6Rh5O15, which was previously refined as a modulated composite [Stitzer, El Abed et al. ( 2001), J. Am. Chem. Soc. 123, 8790-8796], has been refined anew, with equivalent results, as a single modulated structure taking as reference the ideal layered structure. A similar superspace layer description is applied to the recently reported orthorhombic family A(4m+4n) A'(n) B4m+2nO12m+9n. This description allows the a priori derivation of a refineable superspace model that includes the superspace symmetry and crenel functions and is valid for the whole family. This model has been successfully applied to the refinement of the compound Ba12Co11O33 [Darriet et al. (2002), Chem. Mater. 14, 3349-3363].

We report the structure determination of two new phases belonging to the A1+x(A′xB1−x)O3 family of oxides with A=Sr, A′=Cu, and B=Mn, where x=3/11 and x=0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr1+x(CuxMn1−x)O3 family. Their structures were solved in the (3+1) dimensional superspace formalism as modulated composite structures with two subsystems [(Cu,Mn)O3] and [Sr]. The superspace group used to solve the structures is R3̄m(00γ)0s. The first phase (x=3/11), corresponding to the chemical formula Sr14Cu3Mn8O33, was obtained as a single crystal with unit cell parameters of a=9.6025(3) Å and c1=2.5660(8) Å (q=7/11c1∗, Z=3), where c1 is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O3]. The second phase (x=0.3244(1)), is a polycrystalline sample with unit cell parameters of a=9.5933(7) and c1=2.5933(3) (q=0.6622c1∗, Z=3). In both structures, one dimensional chains run along the c-axis which contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr1+x(CuxMn1−x)O3, x=0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S=3/2 for Mn4+ and S=1/2 for Cu2+.

Single crystals of a new Ba–Rh–Ir–O oxide were grown from a molten potassium carbonate flux. The new compound, Ba12Rh9.25Ir1.75O33, is structurally related to the 2H-hexagonal perovskite structure and contains pseudo one-dimensional chains of alternating units of ten face-sharing (Rh/Ir)O6 octahedra and one (Rh/Ir)O6 trigonal prism. The magnetic susceptibility of Ba12Rh9.25Ir1.75O33 is featureless, indicating the absence of magnetic order. The oxide is a semiconductor with a room temperature resistance of 280Ω.

Single crystals of two new osmium-containing triple perovskites, Ba(3)LiOs(2)O(9) and Ba(3)NaOs(2)O(9), were grown from reactive molten hydroxide fluxes in sealed silver tubes. They crystallize in the space group P6(3)/mmc with lattice parameters of a = 5.8025(1) A, c = 14.1468(4) A for Ba(3)LiOs(2)O(9) and a = 5.8858(1) A, c = 14.3451(5) A for Ba(3)NaOs(2)O(9). The magnetic susceptibility of these osmates indicates significant Os-Os coupling within the octahedra pair.

The crystal structure of Sr4Mn2NiO9 has been refined on single crystal. This phase belongs to the series A(1+x)(A'B-x(1-x))O-3 (x = 1/3) related to the 2H-hexagonal perovskite. The structure contains transition metals in chains of oxide polyhedra (trigonal x prisms and octahedra); neighboring chains are separated from each other by the Sr atoms. The sequence of the face sharing polyhedra along the chains is two octahedra + one trigonal prism. Mn occupies the octahedra and Ni is disordered in the trigonal prism with approximate to 80% in the pseudo square faces of the prism and approximate to 20% at the centre. This result has been confirmed by XANES experiments at Mn K and Ni K edges, respectively. Sr4Mn2NiO9 is antiferromagnetic with a Neel temperature at T = 3 K. The Curie constant measured at high temperature is in good agreement with approximate to 80% of the Ni2+ ions in the spin state configuration S = 0. (C) 2001 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Single crystals of Sr(4)Mn(2.09)Cu(0.91)O(9) have been grown by flux synthesis and the structure, closely related to the hexagonal perovskite 2H, was solved from single-crystal X-ray data in space group P321. The structure of Sr(4)Mn(2)CuO(9) is composed of chains of face-sharing polyhedra with a sequence of two octahedra and one trigonal prism. The octahedra are filled by Mn atoms and the Cu atoms are randomly distributed at the centres of the square faces of the trigonal prism. A stacking fault is observed within one of the two chains, which can be attributed to a shifting of the chain along the c axis.

Magnetic susceptibility measurements were carried out for two hexagonal perovskite-type oxides Sr1+x(Mn1−xNix)O3 with slightly different compositions (i.e., x=13 and 0.324). A significant difference in the susceptibilities of the two phases demonstrates the need to control phase compositions accurately. Sr4/3(Mn2/3Ni1/3)O3 consists of two spin sublattices, i.e., the Mn4+ and the Ni2+ ion sublattices. Spin dimer analysis was carried out to examine the relative strengths in the spin exchange interactions of the Mn4+ ion sublattice. The temperature dependence of the magnetic susceptibility of Sr4/3(Mn2/3Ni1/3)O3 was found consistent with a picture in which the Mn4+ ion sublattice has weakly interacting antiferromagnetically coupled (Mn4+)2 dimers, the Ni2+ ion sublattice acts as a paramagnetic system, and the two sublattices are nearly independent.

We report the structure determination on a single crystal of Ba12Co11O33, which belongs to the family of 1-dimensional structures related to the 2H hexagonal perovskite. The structure can be derived from the hcp stacking of [Ba8Co2O18] and [Ba8O24] layers. Assuming a similitude in the building principle with that present in the homologue rhombohedral series based on [A(3)A'O-6] and [A(3)O(9)] layers, a generic model within the superspace formalism of the whole family is proposed and used successfully for Ba12Co11O33. Two different strategies are presented. The first one considers the structure as a commensurate modulated composite containing two subsystems [CoO3] and [Ba]. With the [CoO3] subsystem chosen as the reference, the superspace group is Fddd(00gammac)0s0 with a = 11.4129(2) Angstrom, b = 19.7677(2) Angstrom, c, = 2.4722(1) Angstrom, and q = (6/11)c(1)* (Z = 8 for the formula Ba12/11CoO3). The final global R value is 4.46% for 4625 independent reflections (at a I/sigma(I) > 3 level) and only 123 refineable parameters. The second model follows the natural description of the structure as formed by the uniform hcp stacking of the two types of layers [Ba8Co2O18] and [Ba8O24]. The structure is formulated as BaCo11/12O33/12 (Z = 16) and considered to be a commensurate modulated phase with crenel occupational modulations. The superspace group can be denoted as Xdcd(00gamma(L))qqO with a = 11.4129(2) Angstrom, b = 19.7677(2) Angstrom, c = 4.5324(1) Angstrom, and q = (1/6)c*. The final global R value is 4.36% for the same number of independent reflections and 151 refineable parameters. Both approaches yield similar results, demonstrating for the first time the feasibility of refining these structures as layerlike modulated structures, instead of composites. The chains consist of polyhedra sharing faces formed by 10 consecutive CoO6 octahedra followed by one trigonal prism. Previous models based on simulated and highresolution electron microscopy images are refuted.

The structure of Ba1.1064CoO3 has been solved in the (3+1)-dimensional formalism. The structure is described as a modulated chain composite with two subsystems, [CoO3] and [Ba], respectively. The superspace group is R-3m(00γ)0s with a=9.8842(20) Å, c=2.4785(12) Å, and q=0.5532(4) c* (Z=3). A saw-tooth function was used to model both the occupational and displacive modulations. Each atomic saw-tooth function is defined by its center ○4 along the fourth dimension, its width (Δ), and the maximum amplitude of the displacive modulation (δ). The paper describes how, as a first approximation, the columns (CoO3) can be mainly described by a single free parameter, based on the height difference of the trigonal prisms and octahedra that constitute the transition metal chains. As a result, this superspace formalism requires only a small number of variables to be refined, compared to the conventional superstructure description.

The new oxychloride InTeO3Cl was synthesized from a mixture of In2O3, InCl3 and TeO2. Its structure has been determined from single-crystal X-ray diffraction data. The structure is composed of layers separated by a van der Waals gap. The layers consist of edge-sharing chains of [InO4Cl2] octahedra linked through [TeO3] trigonal pyramids. No free Cl atoms are located between the layers.

Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = 1 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.

Single crystals of Ba8CoRh6O21 were grown out of a potassium carbonate flux. The structure was solved by a general method using the superspace group approach. The superspace group employed was R3m(00γ)0s with a = 10.0431(1) Å, c1 = 2.5946(1) Å and c2 = 4.5405(1) Å, V = 226.60(1) Å3. Ba8CoRh6O21 represents the first example of an m = 5, n = 3 member of the A3n+3mA’nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides and contains chains consisting of six consecutive RhO6 octahedra followed by one distorted CoO6 trigonal prism. These chains in turn are separated from each other by [Ba]∞ chains.