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[en] A new sodium and calcium iron phosphate, NaCaFe₃(PO₄)₄, has been synthesized by a flux method and characterized by single crystal X-ray diffraction, magnetic susceptibility and Moessbauer spectroscopy. The compound crystallizes in the orthorhombic space group Pcab with the parameters a=8.706(4) A, b=9.410(1) A, c=29.211(6) A, V=2393 A³ and Z=8. The structure consists of discrete FeO₆ octahedra and FeO₅ trigonal bipyramids, corner-sharing with PO₄ tetrahedra that form a [Fe₃P₄O₁₆]_n three-dimensional framework with two distinct cavities which are the Na⁺ and Ca²⁺ sites. Moessbauer spectroscopy results confirm those obtained from X-ray diffraction. Magnetic susceptibility indicates an antiferromagnetic behavior with a Neel temperature T_N∼26 K

[en] The compound La₂Ca₂MnO₆(O₂) has been synthesized from La₂Ca₂MnO₇ heated at 1123 K under high pressure (4 GPa) with KClO₃ as oxygen source. The crystal structure has been refined from X-ray powder data in the R3-barm space group. The unit-cell parameters are a=5.6335(2) A and c=17.4879(8) A. Perpendicular to the c-axis, the structure is built up by the periodic stacking of two close packed [LaO₃] layers separated by a layer of composition [Ca₂O₂] containing (O₂)^2- peroxide ions. This oxide belongs to the family of compounds formulated as [A'₂O_2-δ][A_nB_n-1O_3n] for n=2 and δ=0. It is the first member of the series where the thickness of the perovskite slab corresponds to one [BO₆] (B=Mn) octahedron. The structural relationships with La₂Ca₂MnO₇ are discussed and the magnetic properties show that in both phases manganese is tetravalent

[en] A new potassium iron phosphate K₁₁Fe₁₅(PO₄)₁₈O has been synthesized by the flux method and characterized by single-crystal X-ray diffraction. The compound crystallizes in the cubic system with the space group P2₁3 and the cell parameter a=9.917(2) A. The unit cell contains one formula unit K_7.33Fe₁₀(PO₄)₁₂O_0.66. The structure is closely related to that of the Langbeinite-like compounds, the main difference being the existence of a four-coordinated iron atom in the structure of the oxyphosphate. K₁₁Fe₁₅(PO₄)₁₈O adopts a complex three-dimensional network involving corner- and edge-linkage between iron polyhedra, and corner-sharing between phosphorus tetrahedra and iron polyhedra. The Moessbauer spectral parameters are consistent with the structure and reveal the presence of octahedral and tetrahedral sites for the iron(III) in the expected 4:1 ratio. The thermal variation of the magnetic susceptibility shows that the title compound is antiferromagnetic with a Neel temperature T_N=6 K. At high temperature, the susceptibility follows a Curie-Weiss law with C=58.82 emu K mol^-1 and θ_p=-88.39 K. The relationship between the structure of K₁₁Fe₁₅(PO₄)₁₈O and the previous reported trivalent vanadium phosphate K₁₁V₁₅(PO₄)₁₈O will be discussed

[en] Above 850⁰C Cs₄Ni₃CdF₁₂ (which corresponds to the x = 0.25 composition of the CsNi/sub 1-x/Cd/sub x/F₃ solid solution) shows an allotropic transformation from a 12 R to a 10 H-type structure. The high temperature form crystallizes in the hexagonal P6₃/mmc space group with a = 6.238 A and c = 25.362 A. A crystal structure determination shows that the 10-layer packing sequence corresponds to a new structural arrangement of CsF₃ layers and divalent cations. The structure is characterized by units of four octahedra linked by faces and connected to each other by an octahedron sharing only corners. Ni and Cd atoms are partially disordered in the tetrameric units, while the unique octahedron is occupied by cadmium. A phase corresponding to the Cs₅Ni₄CdF₁₅ formula has been isolated, which shows an isostructural powder pattern. (author)

[en] New ternary oxides of formulas Na₅NbO₅ and Na₅TaO₅ have been prepared. They crystallize in the monoclinic system (space group C2/c). The crystal structure of Na₅NbO₅ has been determined. It derives from a NaCl-type structure by ordering of the cations and of the oxygen vacancies in the anionic sublattice, the corresponding formula being Nasub(5/6)Nbsub(1/6)Osub(5/6)vacant sub(1/6). Sodium and niobium have a distorted square-pyramidal surrounding. (author)

[en] The title compounds were synthesized and subsequently studied by inelastic neutron scattering (INS). Energy splittings due to the crystalline electric field (CEF) were directly observed for the octahedral LnX₆^3- units in the Cs₂ALnX₆ series. They can be rationalized in terms of crystal-field theory. In the dimer compounds Cs₃Ln₂Br₉ (Ln³⁺ = Tb, Yb) the energy splitting is the result of the combined action of CEF and exchange interactions. (Auth.)

[en] A number of new hexagonal perovskite-like oxides have been obtained by reacting La₄Ti₃O₁₂ and LaTiO₃. Their crystal structure is based on close-packed stacking of LaO₃ layers and can also be described as consisting of blocks of corners-sharing (TiO₆) octahedra perpendicular to the c-axis, separated by layers of vacant octahedra. The first phase, La₅Ti₄O₁₅, corresponds to the 10H polytypoid with a (hccchhccch) sequence along the c-axis. The second phase, La₆Ti₅O₁₈, corresponds to the 18R polytypoid with a (hcccch)₃ stacking of the LaO₃ layers. La₉Ti₇O₂₇ belongs to the 54R polytipoid with a (hccchhcch)₆ layers stacking. The structure consists of an alternating sequence of La₅Ti₄O₁₅ and La₄TiO₁₂ blocks along the c-axis and thus can be considered as a regular intergrowth between these two phases. The main feature of these new phases is that in each structural unit one of the possible octahedral positions remains unoccupied. These results have been confirmed by refinement of powder XRD data as well as by electron microscopy (SAED, HRTEM) methods

[en] Sodium tetracalcium pentaniobium heptadecaoxide, NaCa₄Nb₅O₁₇, corresponds to the n = 5 term of the homologous A_nB_nO_3n+2 family of structures composed of ABX₃ perovskite layers. The structure consists of perovskite-type blocks of n = 5 layers of NbO₆ octahedra, separated by an interblock region. Successive blocks along the b axis are displaced by 1/2c with respect to each other. The deformation of the NbO₆ octahedra is a minimum at the middle of each block, and increases along the direction of the axis to a maximum at each end of the block. Ca and Na share the same intrablock sites, coordinated by 12 O atoms, whereas only Ca atoms are found in the interblock cavities, at sites with different coordination geometries. (orig.)

[en] The new perovskite-type phases have been isolated in the BaRuO₃ -BaBiO₃ system. The first one, Ba₃Ru₂Bi0₉ crystallizes with a monoclinic symmetry (C2/c S.G.) and can be considered as a slightly distorted hexagonal perovskite of the 6H polytype. The second phase corresponds to a solid solution with the general formula Ba₂Ru_xBi_2-xO₆ (O< x≤0.67) and is isostructural with the monoclinic form of BaBiO₃ (12/m S.G.). The main feature of these phases is that they include not only an atomic rearrangement, but also a charge transfer. In both phases, the Bi³⁺ cations occupy only one type of the possible independent positions and thus force a cationic ordering among the octahedral sites. These new structures have been confirmed by refinements of the X-ray powder data using the Rietveld's method. The valence state of the ruthenium has been confirmed by magnetic measurements. Resistivity measurements have shown that these compounds are semiconductors