共查询到20条相似文献,搜索用时 725 毫秒
1.
The strontium tungstate compound Sr 3W 2O 9 was prepared by a high‐pressure synthesis technique. The crystal structure was determined by single‐crystal X‐ray diffraction and transmission electron microscopy. The structure was found to be a hettotype structure of the high‐pressure phase of Ba 3W 2O 9, which has corner‐sharing octahedra with a trigonal symmetry. Sr 3W 2O 9 has a monoclinic unit cell of C2/ c symmetry. One characteristic of the structure is the breaking of the threefold rotation symmetry existing in the high‐pressure phase of Ba 3W 2O 9. The substitution of Sr at the Ba site results in a significant shortening of the interlayer distances of the [ AO 3] layers ( A = Ba, Sr) and causes a distortion in the crystal structure. In Sr 3W 2O 9, there is an off‐centre displacement of W 6+ ions in the WO 6 octahedra. Such a displacement is also observed in the high‐pressure phase of Ba 3W 2O 9. 相似文献
2.
Ba 0.9R 0.1Co 0.7Fe 0.225Ta 0.075O 3-δ (BRCFT, R = Ca, La or Sr) membranes were synthesized by a solid-state reaction. Metal cation Ca 2+, La 3+ or Sr 2+ doping on A-site partially substituted Ba 2+ in BaCo 0.7Fe 0.225Ta 0.075O 3-δ oxides, and its subsequent effects on phase structure stability, oxygen permeability and oxygen desorption were systematically investigated by XRD, TG-DSC, H 2-TPR, O 2-TPD techniques and oxygen permeation experiments. The partial substitution with Ca 2+, La 3+ or Sr 2+, whose ionic radii are smaller than that of Ba 2+, succeeded in stabilizing the cubic perovskite structure without formation of impurity phases, as revealed by XRD analysis. Oxygen-involving experiments showed that BRCFT with A-site fully occupied by Ba 2+ exhibited good oxygen permeation flux under He flow, reaching about 2.3 mL·min −1 ·cm −2 at 900 °C with 1 mm thickness. Of all the membranes, BLCFT membrane showed better chemical stability in CO 2, owing to the reduction in alkalinity of the mixed conductor oxide by La doping. In addition, we also found the stability of the perovskite structure under reducing atmospheres was strengthened by increasing the size of A-site cation (Ba 2+>La 3+>Sr 2+>Ca 2+). 相似文献
3.
La 0.3(Ba 0.5Sr 0.5) 0.7Co 0.8Fe 0.2O 3?δ is a promising bifunctional perovskite catalyst for the oxygen reduction reaction and the oxygen evolution reaction. This catalyst has circa 10 nm‐scale rhombohedral LaCoO 3 cobaltite particles distributed on the surface. The dynamic microstructure phenomena are attributed to the charge imbalance from the replacement of A‐site cations with La 3+ and local stress on Co‐site sub‐lattice with the cubic perovskite structure. 相似文献
4.
Nano crystalline La 0.85Sr 0.15CoO 3 and ruthenium doped compounds (La 0.85Sr 0.15Co 0.9975Ru 0.0025O 3, La 0. 85Sr 0.15Co 0.995Ru 0.005O 3, La 0.85Sr 0.15Co 0.99Ru 0.01O 3) are synthesized using solution combustion method. Completely characterized samples are studied for electrochemical OER in neutral and basic medium. Significant enhancement in catalytic activity is noticed once Ru is substituted in the cobalt site. With higher doping level of Ru, capacitance also increases as depicted in the CV behavior. Tafel slope measurements indicate that Ru substitution has profound effect as enhancement in the exchange current density is observed in neutral K 2SO 4 medium. Enhancement is anticipated due to substitution of Ru, as the RuO 2 mixed catalyst does not give similar activity. 相似文献
5.
The title compound, cis‐di‐μ‐perfluoroheptanoato‐κ 4O: O′‐bis[dicarbonyl(dimethyl sulfoxide‐κ S)ruthenium(I)]( Ru— Ru), [Ru 2(C 7F 13O 2) 2(C 2H 6OS) 2(CO) 4], is a sawhorse‐type dinuclear ruthenium complex with two bridging perfluoroheptanoate ligands, and with two dimethyl sulfoxide (DMSO) ligands in the axial positions coordinating via the S atoms. It is a new example of a compound with an aliphatic fluorinated carboxylate ligand. The Ru—Ru bond distance of 2.6908 (3) Å indicates a direct Ru—Ru interaction. The compound is an active catalyst in transvinylation of propionic acid with vinyl acetate. 相似文献
6.
On Oxygen Perovskites with Pentavalent Ruthenium A B IIIRu VO 6 with A II = Ba, Sr The perovskites Ba 2B IIIRu VO 6 with B III = La, Nd, Sm, Eu, Gd, Dy, Y, are cubic (B III = La: a = 8,54 4 Å; Y: a = 8,33 7 Å); with a partial order for B III and Ru V. The Sc compound, Ba 2ScRuO 6, has a hexagonal 6 L structure (a = 5.79 5 Å; c = 14.22 9 Å; sequence (hcc) 2) 2. The lattice of the Sr perovskites, Sr 2B IIIRu VO 6, with B III = Eu, Gd, Dy, Y is rhombic distorted. The IR and FRI spectra are discussed. 相似文献
7.
The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula Ba MRu 5O 11 ( M=Li and Cu) and Ba M′ 2Ru 4O 11 ( M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P6 3/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn 2Ru 4O 11 is reported. 相似文献
8.
La1-xAxCoO3-δ (A = Sr, Ba) nanoparticles used as an inert anode in molten salts were characterized using phonon vibrations, and their compositions and morphologies were investigated. These nanoparticles were used for nanostructure fabrication of an inert anode to reduce oxide ion transportation. The singularity structure changes with increasing Sr ion content in La1-xSrxCoO3-δ nanoparticles showed a transient of spin state change from a low-spin state to intermediate- and/or high-spin states. The valencies of Co ion in La1-xSrxCoO3-δ were 3.2 and 3.3 for La0.8Sr0.2CoO3-δ and La0.6Sr0.4CoO3-δ, respectively, suggesting that oxygen defects were introduced by Sr ion doping in La1-xSrxCoO3-δ nanoparticles. In contrast, the valencies of Co ion in La1-xBaxCoO3-δ were 3.1 and 3.0 for La0.5Ba0.5CoO3-δ and La0.4Ba0.6CoO3-δ, respectively, suggesting that oxygen defects were introduced slightly by Ba ion doping in La1-xBaxCoO3-δ nanoparticles. The isotropic phonon vibrations of La1-xAxCoO3-δ nanoparticles were estimated using high-temperature synchrotron radiation X-ray diffraction measurements. Crystal anisotropy measurements of phonon vibrations indicated that the oxide ions diffused preferentially along the (a, b) plane in the La1-xSrxCoO3-δ crystal lattice and toward the c-axis direction in the La1-xBaxCoO3-δ crystal lattice. These results suggest that the oxide ion transportation was curtailed using layered nanoparticles to fabricate an inert anode. 相似文献
9.
Tetrapnictidotitanates(IV) M 4TiX 4 (M = Sr, Ba; X = P, As), hierarchical Derivatives of the KGe Structure K 4□Ge 4 The four new tetrapnictidotitanates(IV) Sr 4TiP 4, Sr 4TiAs 4, Ba 4TiP 4 and Ba 4TiAs 4 are synthesized from the binary pnictides MX (M = Sr, Ba and X = P, As) and elementary titanium in tantalum ampoules. The compounds are isotypic and isoelectronic with Ba 4SiAs 4 (space group P4 3 n (no. 218); cP72; Z = 8; Sr 4TiP 4: a = 1259.0(1) pm; Sr 4TiAs 4: a = 1288.3(4) pm; Ba 4TiP 4: a = 1316.6(2) pm; Ba 4TiAs 4: a = 1346.9(2) pm). The transition metal compounds form cubic, metallic reflecting crystals (Sr 4TiP 4 (green); Sr 4TiAs 4 (silver coloured); Ba 4TiP 4 (silver coloured); Ba 4TiAs 4 (violet). They are semiconducting and very sensitive against air and moisture. The structure is a hierarchical derivative of Cr 3Si (A15) and KGe type: Cr 6Si 2 ? (□Ge 4K 4) 6(□Ge 4K 4) 2 ? (TiX 4M 4) 6(TiX 4M 4) 2, where Ti occupies the positions of the Cr 3Si structure, and the alkaline-earth metal and pnicogen atoms occupy the positions of the KGe structure. Therefore, Ti is surrounded by four X and four more distant M atoms forming a heterocubane. The mean bond lengths are: d (Ti? P) = 238.0(5) pm; 307 ? d(Sr? P) ? 333 pm; d (Ti? As) = 245.9(4); 313 ? d(Sr? As) ? 341 pm; d (Ti? P) = 240.5(5); 324 ? d(Ba? P) ? 348 pm; d (Ti? As) = 248.3(3) pm; 331 ? d(Ba? As) ? 355 pm. 相似文献
10.
Sodium insertion in the tetrahedral layer structure of the ferrites Ba 2−xSr xFe 4O 8 was performed by solid state reaction at 1220 K in air. Superstoichiometric oxides with the actual formula (Ba 2−xSr x) 1−y/4Na yFe 4O 8— y0.56; 0.60Ba/Sr1.67—were characterized by X-ray and neutron powder diffraction. The hexagonal unit-cell volume shows an increasing dependence on the sodium insertion when the Ba/Sr ratio reaches the largest values. The marked expansion of the c parameter is the likely signature of the location of the inserted sodium cations within the interlayer space. One-half of the sodium cations partly sits on the Sr(Ba) sites in octahedral coordination and the other half occupies extra octahedral and tetrahedral sites. ac conductivity measurements point to a cationic conductivity whose thermally activated regime— Ea 0.7 eV—evidenced from 570 K, is unsensitive to the sodium content. The bottleneck of the 2D sodium mobility regards the crossing of the oxygen triangular faces shared by the different polyhedra within the interlayer space. 相似文献
11.
Strontium borophosphate, Sr 6BP 5O 20, was prepared by a solution synthesis method. The crystal structure was solved ab initio from synchrotron powder data without preliminary knowledge of the chemical formula. The compound crystallizes in space group Ic2. Sr atoms occupy sites coordinated by eight or nine O atoms, and the anionic layer consists of BO 4 and PO 4 tetrahedra. The eightfold‐coordinated Sr atom lies at a site with twofold symmetry, while one P atom and the B atom are located on special positions of site symmetry . 相似文献
12.
Ba 2La 4Ti 5O 18 crystallizes in the trigonal system (space group R3) with the unit-cell parameters: a = 5.584 (1) Å; c = 41.176 (8) Å; Z= 3.The structure has been solved from single crystal X-ray diffraction data to a final R 1 = 0.0285. Ba and La atoms are twelve-fold coordinated and Ti atoms six-fold coordinated. The structure can be described as consisting of identical perovskite-like blocks, five corner-sharing TiO 6 octahedra thick, separated by layers of vacant octahedra. The distortion of the cation and anion sublattices has been analysed and a Ba/La order has been evidenced. 相似文献
13.
Strontium barium niobate crystals with congruent melting composition Sr 0.61Ba 0.39Nb 2O 6 (SBN-61), both nominally pure and doped with Cr 3+ и Ni 3+ ions, have been investigated by neutron diffraction. Different strontium and barium contents as well as their different distribution over the Sr1, of Sr2 and Ba2 crystallographic sites of SBN-61 structure, caused by introduction of dopants, have been revealed. Coordination polyhedra of cations have been established based on the analysis of cation–anion internuclear distances together with the calculation of bond-valence sums for cations, which are equal to their formal charge. It was found that the Nb1 and Nb2 atoms are located in distorted octahedra with quadfurcated (the Nb1O 6 polyhedron) or bifurcated (the Nb2O 6 polyhedron) vertices, and the Sr1 atoms are located in a cuboctahedron with bifurcated vertices in the base plane. Different polyhedra have been revealed for the Sr2 and Ba2 atoms: Sr2 atoms are coordinated by 15 oxygen atoms to form a highly distorted five-capped pentagonal prism, whereas Ba2 atoms are located in a highly distorted three-capped trigonal prism with a coordination number 9. Comparison of interatomic and internuclear distances, determined by X-ray and neutron diffraction analyses, respectively, allowed to reveal a highly pronounced shift of electron density in Nb1 and Sr2 polyhedra, responsible for the covalent bond and properties of crystals. Location of Cr 3+ и Ni 3+ dopant ions in the SBN-61 structure as well as their formal charges has been discussed. 相似文献
14.
LaNiO 3 perovskite is an interesting precursor for Ni/La 2O 3 catalysts for the dry reforming of methane at high temperatures. Precursors have been synthesized by co‐precipitation without, with 2.5 at %, and with 5 at % Ru doping. The presence of Ru leads to a stabilization of the perovskite structure and hinders the decomposition into NiO and Ruddlesden‐Popper mixed oxides La n+1Ni nO 3n+1, which was observed for the Ru‐free sample upon calcination at 1000 °C ( n = 3). Upon reduction in hydrogen, a mechanism involving at least two steps was observed and the first major step was identified as the partial reduction of the precursor leading to a LaNiO 2.5‐like intermediate. The second major step is the reduction to Ni metal supported on La 2O 3 independent of the Ru content of the catalyst. In the presence of Ru, indications for Ni‐Ru alloy formation and for a higher dispersion of the metallic phase were found. The catalytic activity in DRM of the catalyst containing 2.5 % Ru was superior to the catalysts with more or without Ru. Furthermore, the propensity of coke formation was reduced by the presence of Ru. 相似文献
15.
Single‐crystal X‐ray diffraction has shown that lanthanum barium manganese trioxide, La 0.815Ba 0.185MnO 3, is monoclinic ( I2/ c) below a first‐order phase transition at 187.1 (3) K. This result differs from the Pbnm symmetry usually assigned to colossal magnetoresistance oxides, A1−xA′ xMnO 3 with x≃ 0.2, which adopt a distorted perovskite‐type crystal structure. The Mn atom lies on an inversion center, the disordered Li/Ba site is on a twofold axis and one of the two independent O atoms also lies on a twofold axis. 相似文献
16.
Compounds of the Type Ba 3B IIM O 9 with B II ? Mg, Ca, Sr, Ba, and M V ? Nb, Ta The hexagonal perovskites Ba 3B IIMO 9 (M V ? Nb, Ta) crystallize with B II ? Mg Ca in a 3 L structure (sequence (c) 3) and B II ?; Sr in the hexagonal BaTiO 3 type (6 L; sequence (hcc) 2) with an 1:2 order for the B and M ions. Intensity calculations for Ba 3SrNb 2O 9 and Ba 3SrTa 2O 9 gave in the space group P6 3/mmc a refined, intensity related R′ value of 8.4% (Nb) and 9.0% (Ta) respectively. For B II ? Ba the perovskite Ba 3BaTa 2O 9 has an orthorhombic distorted 6 L structure and forms with Ba 3SrTa 2O 9 a continuous series of mixed crystals (Ba 3Sr 1?xBa xTa 2O 9). In the system Ba 3Sr 1?xBa xNb 2O 9 the range of existence of the hexagonal BaTiO 3 type is confined to the Sr richer end. The pure Ba compound possesses a proper structure type (5 L: Ba 5BaNb 3□O 13.5□ 1.5). 相似文献
17.
The tribarium dilithium divanadate tetrachloride Ba 3Li 2V 2O 7Cl 4 is a new vanadate with a channel structure and the first known vanadate containing both Ba and Li atoms. The structure contains four non‐equivalent Ba 2+ sites (two with m and two with 2/ m site symmetry), two Li + sites, two nonmagnetic V 5+ sites, five O 2− sites (three with m site symmetry) and four Cl − sites ( m site symmetry). One type of Li atom lies in LiO 4 tetrahedra ( m site symmetry) and shares corners with VO 4 tetrahedra to form eight‐tetrahedron Li 3V 5O 24 rings and six‐tetrahedron Li 2V 4O 18 rings; these rings are linked within porous layers parallel to the ab plane and contain Ba 2+ and Cl − ions. The other Li atoms are located on inversion centres and form isolated chains of face‐sharing LiCl 6 octahedra. 相似文献
18.
The phase transitions of Ba 2-xSr xIn 2O 5 were investigated with various thermal analyses and high-temperature X-ray diffraction. It was clarified that crystal structure
of Ba 2-xSr xIn 2O 5 with x=0.0~0.4 varies from brownmillerite through distorted perovskite to another distorted perovskite with increase of temperature.
The phase transition from brownmillerite to distorted perovskite was revealed to be first order, whereas transition from distorted
perovskite to another one was second order. The specimen with x≥0.5 showed only one first order phase transition from brownmillerite to distorted perovskite. The phase diagram of Ba 2-xSr xIn 2O 5 was established and existence of tricritical point at ~1100°C with x=0.4~0.5 was suggested.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
19.
The series of compounds M2EuRuO 6 ( M = Ca, Sr, Ba) has been studied by 151Eu Mössbauer spectroscopy. X-Ray data show them to be structurally derived from the ABO 3 perovskite lattice, but only the Ba compound gives positive evidence to suggest ordering of the cations. The 151Eu resonance shows magnetic hyperfine splitting at 4.2 K. The Ru 5+OEu 3+ORu 5+ exchange takes place by admixture of low-lying excited states into the diamagnetic J = 0 ground-state of the Eu 3+. The Curie temperatures are approximately 18, 31, and 42 K for the Ca, Sr, and Ba compounds. Detailed analysis shows that substantial disorder of cations occurs, being quite large for Ca, <8% for Sr, and <5% for Ba. However, it appears that considerable canting of the Ru 5+ spins takes place in the Ba compound immediately below the Curie temperature as a result of the disorder and low anisotropy at the Ru sites. This effect is much reduced in the more distorted Sr compound. 相似文献
20.
Three new compounds in the AE‐Si‐P ( AE = Sr, Eu, Ba) systems are reported. Sr 2SiP 4 and Eu 2SiP 4, the first members of their respective ternary systems, are isostructural to previously reported Ba 2SiP 4 and crystallize in the noncentrosymmetric I4 2 d (no. 122) space group. Ba 4Si 3P 8 crystallizes in the new structure type, in P2 1/ c (no. 14) space group, mP‐120 Pearson symbol, Wyckoff sequence e30. In the crystal structures of Sr 2SiP 4 and Eu 2SiP 4 all SiP 4 tetrahedral building blocks are connected via formation of P–P bonds forming a three‐dimensional framework. In the crystal structure of Ba 4Si 3P 8, Si‐P tetrahedral chains formed by corner‐sharing, edge‐sharing, and P–P bonds are surrounded by Ba cations. This results in a quasi‐one‐dimensional structure. Electronic structure calculations and UV/Vis measurements suggest that the AE2SiP 4 ( AE = Sr, Eu, Ba) are direct bandgap semiconductors with bandgaps of ca. 1.4 eV and have potential for thermoelectric applications. 相似文献
|