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1.
We report the synthesis and crystal structure of the new compound Sr4PbPt4O11, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R=0.0260 and wR=0.0262. The symmetry is triclinic, space group P1¯, with , , , α=90.421(3)°, β=89.773(8)°, γ=90.140(9)° and Z=2. The structure is built from dumbell-shaped Pt2O9 entities formed by a dinuclear metal-metal bonded Pt26+ ion with asymmetric environments of the two Pt atoms, classical PtO4 square plane and unusual PtO5 square pyramid. Successive Pt2O9 entities deduced from 90° rotations are connected through the oxygens of the PtO4 basal squares to form [Pt4O108−] columns further connected through Pb2+ and Sr2+ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.  相似文献   

2.
The local environments for oxygen in yttrium-containing pyrochlores and fluorites, Y2(B1−xBx)2O7 (B=Ti, B′=Sn, Zr) are investigated by using solid state 17O MAS NMR spectroscopy. The quadrupolar coupling constants of the nucleus, 17O are sufficiently small for these ionic oxides, that high-resolution spectra are obtained from the MAS spectra. Different oxygen NMR resonances are observed due to local environments with differing numbers of metal cations (Y3+, Sn4+, Ti4+ and Zr4+), allowing the numbers of different local environments to be quantified and cation mixing to be investigated. Evidence for pyrochlore-like local ordering is detected for Y2Zr2O7, which nominally adopts the fluorite structure.  相似文献   

3.
The crystal structure and stability of Ba4CaCu3O8+δ have been investigated by neutron powder diffraction, differential thermal analysis and thermogravimetry. It is found that the phase is not stable below 1065 K in p(O2)=1 bar and decomposes according to the eutectoid reaction Ba4CaCu3O8+δ+x O2⇒Ba2CuO3.4+CaO+2BaCuO2. However, the equilibrium with the outer gas is not reached for sintered ceramics so that Ba4CaCu3O8+δ can be obtained in a metastable state after normal cooling conditions. In this case, the crystal structure is cubic (Im-3m, , δ=0.68, Z=2, Rwp=2.5%, RBragg=5.4%) as reported in the literature. In reduced oxygen partial pressure (p(O2)<10−6 bar), Ba4CaCu3O8+δ is stable down to room temperature and has a tetragonal structure with a significant lower oxygen content (P4/mmm, , , δ=-0.81, Z=2, Rwp=2.8%, RBragg=5.1%). The difference between the two crystal structures is discussed in terms of oxygen content, copper formal valence and cation coordination. The influence of the oxygen pressure on the stability of Ba4CaCu3O8+δ is also discussed.  相似文献   

4.
5.
The new magnesium rhodium boron compound Mg8Rh4B has been synthesized by reaction of the metal powders with crystalline or amorphous boron or the RhB precursor. The crystal structure of Mg8Rh4B was solved using single-crystal X-ray diffraction data (space group , , Z=8, 174 reflections, RF=0.016). The crystal structure can be described as a filled Ti2Ni type where the interstitial sites 8b (), located at the center of two nested Mg4Rh4 tetrahedra, are occupied by boron atoms. Taking into account the absence of the Ti2Ni-type phase in the binary Mg-Rh system, the boron atoms can be considered as stabilizing this structural motif. From the bonding analysis with the electron localization function the crystal structure is described as covalently bonded [Rh4B]3− anions, embedded in a cationic magnesium matrix.  相似文献   

6.
A new Ca6.3Mn3Ga4.4Al1.3O18 compound has been prepared by solid state reaction in a dynamic vacuum of 5×10−6 mbar at 1200 °C. The crystal structure of Ca6.3Mn3Ga4.4Al1.3O18 was studied using X-ray powder diffraction (, SG F432, Z=8, RI=0.031, RP=0.068), electron diffraction and high resolution electron microscopy. The Ca6.3Mn3Ga4.4Al1.3O18 structure can be described as a tetrahedral [(Ga0.59Mn0.24Al0.17)15O30]18.24− framework stabilized with embedded [(Ca0.9Mn0.1)14MnO6]18.24+ polycations, which consists of an isolated MnO6 octahedron surrounded by a capped cube of (Ca0.9Mn0.1) atoms. The Ca6.3Mn3Ga4.4Al1.3O18 structure is related to the structure of Ca7Zn3Al5O17.5, but appears to be significantly disordered due to the presence of two orientations of oxygen tetrahedra around the cationic 0,0,0 and x,x,x () positions in a random way according to the F432 space symmetry. The analogy between the Ca6.3Mn3Ga4.4Al1.3O18 crystal structure and the structure of the “fullerenoid” Sr33Bi24+δAl48O141+3δ/2 oxide is discussed. Ca6.3Mn3Ga4.4Al1.3O18 adopts a Curie-Weiss behavior of χ(T) above with a Weiss temperature and per formula unit. At lower temperatures, the χ(T) deviates from the Curie-Weiss law indicating a strengthening of the ferromagnetic component of the exchange interaction.  相似文献   

7.
Structural and magnetic studies are presented for the perovskite type Sr1−xLaxCo0.5Fe0.5O3−δ (0?x?0.5) materials annealed under moderately high-oxygen pressures of ∼200 atm. A detailed analysis of the room temperature neutron time-of-flight diffraction data reveals that the crystal structure of the sample SrCo0.5Fe0.5O2.89(1), previously described as vacancy-disordered cubic, is similar to the formerly reported, oxygen-vacancy ordered Sr8Fe8O23 compound, i.e. Sr8Co4Fe4O23 is tetragonal with the I4/mmm symmetry. With an increase of the La content the studied materials become nearly oxygen stoichiometric and a lowering of the crystal symmetry is observed from cubic (x=0.1 and 0.2) to tetragonal I4/mcm (x=0.3 and 0.4), and finally to monoclinic I12/c1 (x=0.5). Low-temperature structural and magnetic measurements show a ferromagnetic ordering with the maximum Curie temperature near 290 K at x=0.2.  相似文献   

8.
The compound previously reported as Ba2Ti2B2O9 has been reformulated as Ba3Ti3B2O12, or Ba3Ti3O6(BO3)2, a new barium titanium oxoborate. Small single crystals have been recovered from a melt with a composition of BaTiO3:BaTiB2O6 (molar ratio) cooled between 1100°C and 850°C. The crystal structure has been determined by X-ray diffraction: hexagonal system, non-centrosymmetric space group, a=8.7377(11) Å, c=3.9147(8) Å, Z=1, wR(F2)=0.039 for 504 unique reflections. Ba3Ti3O6(BO3)2 is isostructural with K3Ta3O6(BO3)2. Preliminary measurements of nonlinear optical properties on microcrystalline samples show that the second harmonic generation efficiency of Ba3Ti3O6(BO3)2 is equal to 95% of that of LiNbO3.  相似文献   

9.
Phase relations at 700 °C, 800 °C and solidus temperatures have been derived for the clathrate system Ba8CuxGe46−xyy via X-ray single crystal and powder diffractometry combined with electron probe micro analysis and differential thermal analysis. The ternary clathrate phase derives from binary Ba8Ge433 and extends up to x=6. Structure investigations define cubic primitive symmetry with the space group type consistent with a clathrate type I structure throughout the entire homogeneity region 0<x?6 but defect-free Ba8CuxGe46−x exists for x?5.5.  相似文献   

10.
The crystal structures of three new intermetallic ternary compounds in the LnNiSb3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb3, NdNiSb3 and SmNiSb3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Effective moments of 3.62 μB, 3.90 μB and 0.80 μB are found for PrNiSb3, NdNiSb3 and SmNiSb3, respectively, and are consistent with Pr3+ (f 2), Nd3+ (f 3), and Sm3+ (f 4).  相似文献   

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