Recent advances in the study of Aurivillius phases (Bi2A n -1BnO3n+3, n = 1−5) as oxide ion conductors are presented. The structures of modified Aurivillius phases containing extrinsic oxygen vacancies as well as Aurivillius phases containing intrinsic oxygen vacancies are surveyed. A detailed discussion of the conductivity behavior of these Aurivillius phases is given.

The solid-state structures of a series of 2,5-dialkyl-substituted poly(p-phenyleneethynylene)s (PPEs 4, R = hexyl, dodecyl, isopentyl, ethylbutyl, ethylhexyl, H) and of 2,5-didodecyl(1,4-phenylenebutadiynylene) were investigated by X-ray powder and electron diffraction. In addition, X-ray single-crystal structures of the monomeric (1,4-dipropynyl-2,5-dialkyl)benzenes were obtained and compared to the structures of the corresponding polymers. In the case of the ethylhexyl-substituted PPE, the packing of the monomer resembles that of the polymer in the solid state. All of the examined PPEs show lamellar morphologies, in which the extended geometry of the side chains determines the value of the lamellar spacing obtained by powder diffraction. A second d value, which could be obtained for all samples represents the π−π-stacking distance of the main chains. This distance is around 3.8 Å, a typical value for stacking of aromatic systems. It implies strong electronic interaction of the chromophoric backbones, leading to the observed sharp aggregate band in CHCl3/MeOH solutions and in thin films. From the scattering data, staggered packing of the benzene rings and the phenyleneethynylene main chains in PPEs 4 was inferred. This packing avoids repulsive electrostatic interactions between adjacent conjugated phenyleneethynylene chains and at the same time leads to optimal packing of the side chains.

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During recent years, there has been much interest in the preparation and investigation of oxides structurally related to the 2H hexagonal perovskites, the prototype of which, Sr 4 PtO 6 , was first prepared by Randall and Katz 1 and forms in the K 4 CdCl 6 structure type. As shown by Darriet and Subramanian, 2 and more recently by Darriet and Perez-Mato, 3 the structures of these oxides can all be described as resulting from stacking sequences of m[A 3 O 9 ] layers and n[A 3 AAO 6 ] layers, with the subsequent filling of the interstitial octahedral sites. The general formula that can be derived from the stacking of such layers is: A 3n + 3m AA n B 3m + n O 9m + 6n (n, m = integers, A = alkaline earth; AA, B = large assortment of metals including alkali, alkaline earth, transition, main group, and rare earth metals). The structures are characterized by one-dimensional chains of face-sharing trigonal prisms and octahedra along the c-axis of the hexagonal unit cell.Sr 4 PtO 6 is the n = 1, m = 0 member of this family and consists of chains of alternating face-sharing octahedra and trigonal prisms. While many n = 1, m = 0 members are known, for example Sr 3 NaRhO 6 , 4 Ca 3 Co 2 O 6 , 5,6 and Ca 3 CuIrO 6 , 7 far fewer oxides with higher integer values of n and m have been prepared and structurally characterized. In addition, until recently, most structure determinations were based on Rietveld refinements of polycrystalline powders and few single crystals of any members, and in particular very few members with higher integer values of n and m, have been grown and structurally characterized. A recent example of the latter type includes Ba 8 CoRh 6 O 21 corresponding to the m = 5, n = 3 member. 8 Other examples include Ba 6 Ni 5 O 15 , 9 Sr 4 Ru 2 O 9 , 10 and the incommensurate phases of Ba 1 + x (Cu x Rh 1 2 x )O 3 (x = 0.1605 and 0.1695) whose average structure is that of the n = 3, m = 4 member with a repeat sequence of five octahedra and one trigonal prism. 11 In this communication we report the first structural characterization of the m = 2, n = 1 member Ba 9 Rh 8 O 24 and the investigation of its magnetic properties.Single crystals of Ba 9 Rh 8 O 24 were grown from a molten potassium carbonate flux. BaCO 3 and Rh metal powder (6:1 molar ratio) were mixed with a 10 fold mass excess of K 2 CO 3 . The alumina crucible was heated in air to 1050 °C, held for 48 h, and then quickly cooled to room temperature. The crystals were isolated manually by dissolving the flux in water.An approximate [110] view is shown in Fig. 1. The structure is characterized by infinite chains containing groups of seven face-sharing RhO 6 octahedra separated by one face-sharing RhO 6 trigonal prism. These chains are in turn separated from one another by chains of Ba cations. The metal-oxygen bond distances [Rh1-O1 2.020(6), Rh2-O2 2.008(6), Rh2-O1 2.035(6), Rh3-O3 2.003(7), Rh3-O2 2.035(6), Rh4-O4 1.969(10), Rh4-O3 2.048(7), Rh5-O4 2.012(12) Å] are typical for oxides of this type. Intrachain Rh-Rh bond distances [Rh1-Rh2 2.523(1), Rh2-Rh3 ...