室温电化学沉积Ba1-xCaxMoO4多晶固溶体薄膜

近年发展起来的制备功能薄膜的电化学沉积技术,是软溶液工艺路线(Soft Solution Processing简记为SSP)中的重要技术[1]。与传统的薄膜制备技术相比,电化学沉积技术在反应控制、形貌控制、沉积速度、能量消耗、环境影响、薄膜晶化以及沉积设备等方面都有较明显的优势,同时避免了     

Zur Kenntnis von Ba6La2Co4O15

About Ba₆La₂Co₄O₁₅ Ba₆La₂Co₄O₁₅ were prepared and investigated by X-ray single crystal work. It crystallizes with hexagonal symmetry, space group C–P6₃mc; a = 11.8082; c = 7.0019 Å; Z = 2. Ba²⁺ show face connected BaO₆-octahedra and larger polyhedra of C.N. = 10 and 12. Co³⁺ is surrounded by four and six (tetrahedra, octahedra) oxygen. The Ba²⁺ and La³⁺ ions occupy one point position statistically.     

Techniques for obtaining far infrared transmission spectra of high Tc,superconductors and related synthetic precursors

The far infrared (FT-IR) spectra of Y₂O₃, CuO, BaO₂, YBa₂Cu₃O_7−σ and Tl₂Ca₂Ba₂Cu₃O₁₀ have been recorded in the range of 350-60 cm⁻¹. A variety of sample handling techniques have been utilized which include dispersion of the samples in nujol and fluorolube. Additionally, we present preliminary results of a technique of preparing thin films (1–20 μm thick) of these materials. These films do not require a substrate but are dispersed in a polyethylene matrix fused between two polyethylene plates. Such films are suitable for optical applications.     

EXAFS and XANES Studies of Silica-Titania Sol-Gel Films

A series of SiO₂-TiO₂ sol-gel films with and without heat treatment were analyzed by EXAFS and XANES spectroscopies. Both techniques indicate that essentially all Ti⁴⁺ ions remain four-fold coordinated, with a Ti–O bond distance between 1.82–1.85 Å. In the glassy films produced by heat treatment at 900° C, a gradual phase separation may occur at the nanoscale, as the TiO₂ concentration of the films increases.     

Zur Kenntnis eines Oxoargentato(I)-aurats(III): Ba4AgAuO6

On the Oxoargentato(I)-aurat(III): Ba₄AgAuO₆ The hitherto unknown compound Ba₄AgAuO₆ was prepared by oxidizing Ba/Au/Ag alloy with BaO₂/Ba(OH)₂ mixture in closed Ag tubes. X-ray single crystal investigation led to orthorhombic symmetry space group D-Cmcm; a = 13.275; b = 5.782; c = 11.396 Å; Z = 4. Ba₄AgAuO₆ shows distorted pentagonal bipyramidal polyhedra around Ba²⁺ and square planar AuO₄ polygones. Ag⁺ shows an unusual 2 + 2 coordination by O^2?.     

Ein neuer Strukturtyp mit flächenverknüpften BaO6-Oktaedern: Ba6Nd2Al4O15

Summary A compound Ba₆Nd₂Al₄O₁₅ with a new structure-type was prepared by solid state reaction. It crystallizes with hexagonal symmetry, space group C _6v ⁴ – P 6₃mc;a=11.5696;c=6.9662 Å;z=2. Ba₆Nd₂Al₄O₁₅ has a dominating Ba/O-framework with incorporated AlO₆-octahedra and AlO₄-tetrahedra. A main feature of the structure are face connected BaO₆-octahedra. One of the point positions of the heavy atoms is occupied statistically by Ba²⁺ and Nd³⁺.

     

Dopant substitution and oxygen migration in the complex perovskite oxide Ba3CaNb2O9: A computational study

Atomistic simulation methods have been used to study the defect chemistry of the complex perovskite oxide Ba₃CaNb₂O₉. Calculations were carried out for the hexagonal (P-3m1) phase and the cubic (Fm-3m) phase. The hexagonal structure is predicted to be energetically more stable at room temperature. In both structures the most favourable dopant for Nb⁵⁺ is found to be Ca²⁺ rather than Mg²⁺, in contrast to the generally accepted rule that size similarities govern such processes. The diffusion of oxygen vacancies in the hexagonal and cubic phases occurs within different networks of corner-sharing NbO₆ and CaO₆ octahedra. Irrespective of the arrangement of octahedra, however, migration of oxygen vacancies around NbO₆ octahedra takes place with lower activation energies than around the CaO₆ octahedra.     

New Ba5M5−xPtxClO13 (M=Fe, Co) oxychlorides with layered perovskite-related structure

Crystals of Ba₅Fe_5−xPt_xClO₁₃ and Ba₅Co_5−yPt_yClO₁₃ were prepared for x=1.31, 1.51, 1.57, 1.59 and y=0, 0.97 and 1.08 in a BaCl₂ flux and investigated by X-ray diffraction methods. These compounds adopt a 10H perovskite structure built from the stacking of BaO₃ and BaOCl layers in the sequence (BaO₃)₄(BaOCl) with space group P6₃/mmc. The cation sites within the trimeric unit of face-sharing octahedra are occupied by Co or Fe and Pt ions, while the tetrahedral sites formed between BaO₃ and BaOCl layers are only occupied by Fe or Co. Moreover, oxygen stoichiometry indicates an average oxidation state for Co and Fe higher than +III, indicating the stabilization of Co⁴⁺ and Fe⁴⁺.     

Cation and anion ordering in the layered oxyfluorides Sr3−xAxAlO4F (A=Ba, Ca)

The synthesis and structural characterization of mixed oxyfluorides of the type Sr_3−xA_xAlO₄F is reported, where A is either calcium or barium. In these compounds the fluoride and oxide ions are ordered onto two distinct crystallographic sites. There is also an ordering of the alkaline earth cations over two crystallographic sites upon substitution of Ba²⁺ or Ca²⁺ for Sr²⁺. The solid solubility limits extend to x∼1 for substitution of both barium and calcium, but the larger Ba²⁺ cations show a strong site preference for the ten-coordinate strontium sites, while the smaller Ca²⁺ cations prefer the eight-coordinate strontium sites.     

Structure of ten-layer orthorhombic Ba5Fe5O14 (BaFeO2.8) determined from single crystal X-ray diffraction

The structure of the mixed-valent Ba₅Fe₅O₁₄ (BaFeO_2.8), prepared using a molten KOH-Ba(OH)₂ flux, has been determined using single crystal X-ray diffraction. Ba₅Fe₅O₁₄ forms twinned crystals with the orthorhombic space group Cmcm, a=5.7615(8), b=9.9792(14) and c=24.347(3) Å, Z=4. The structure, which is closely related to the 10H BaFeO_2.65 perovskite, is composed of two oxygen-deficient BaO₂ layers and eight BaO₃ layers with a (hchhc)₂ stacking sequence, where h and c denote hexagonal or cubic layers. A displacement of barium and oxygen atoms in the BaO₂ layers from hexagonal special positions lowers the symmetry from hexagonal to orthorhombic. This combination of stacking and vacancies creates trimers of face-sharing FeO₆ octahedra pillared by dimers of corner-sharing FeO₄ tetrahedra. The Fe⁴⁺ atoms are located in the center of the trimer and in the tetrahedral sites. The magnetism of Ba₅Fe₅O₁₄, investigated using SQUID magnetometry, is characteristic of a strongly coupled antiferromagnet.     

The six-layer structure of BaSn0.9Fe5.47O11

The crystal structure of BaSn_0.9Fe_5.47O₁₁ was determined using neutron powder diffraction data and the profile refinement method. The hexagonal compound, space group , has hcc-stacked BaO₃ and O₄ layers. A new building unit for this type of structure is introduced, the Q block with formula Ba₂M₇O₁₄, consisting of two c-stacked BaO₃ layers and two O₄ layers. Between the BaO₃ and O₄ layers one tetrahedral and one octahedral site is occupied; between the BaO₃ layers there are no other cations. BaSn_0.9Fe_5.47O₁₁ shows a magnetic behavior with an ordering temperature T_c of 420 K. Starting models for the structure determination were derived from the known structures of hexagonal ferrites and related compounds. Several isomorphs with formula Ba₂Sn₂M²⁺Fe₁₀O₂₂ could be prepared, in which a partial substitution of Fe by Ga is possible. The nonstoichiometry of BaSn_0.9Fe_5.47O₁₁ can be explained by the surplus of positive charge if the available tetrahedral and octahedral sites of the structure are completely occupied with Sn⁴⁺ and Fe³⁺. To achieve charge compensation either the occupation rates of Sn⁴⁺ and Fe³⁺ have to be lowered or a divalent ion has to be introduced, as is effected in the isomorphs.     

Investigation in SrTiO<Subscript>3</Subscript>-CaTiO<Subscript>3</Subscript>-PbTiO<Subscript>3</Subscript> ternary thin films by dielectric proprieties and Raman spectroscopy

Dielectric and Raman scattering experiments were performed on polycrystalline Pb_1−x−yCa_xSr_yTiO₃ thin films as a function of temperature. Temperature-dependent dielectric measurements revealed a decreasing ferroelectric-to-paraelectric phase transition temperature and peak dielectric permittivity showed a broad phase transition near room temperature with increasing levels of CaO₁₂ and SrO₁₂ clusters. Therefore, for higher levels of substitution, the possible random position of the CaO₁₂ and SrO₁₂ clusters leads to a diffuse state. At 100 kHz, the ferroelectric-to-paraelectric phase transition temperatures were 633, 495 and 206 K for PCST90 (Pb_0.90Ca_0.05Sr_0.05TiO₃), PCST70 (Pb_0.70Ca_0.15Sr_0.15TiO₃) and PCST30 (Pb_0.30Ca_0.35Sr_0.35TiO₃) thin films, respectively. The evolution of the Raman spectra was also studied as a function of temperature. The temperature dependence of the E(1TO) soft mode frequencies was used to characterize the phase transition. Raman peaks were observed above the ferroelectric-to-paraelectric phase transition temperature, although all optical modes should be inactive in Raman scattering. The origin of these modes was interpreted as a breakdown of the local cubic symmetry by the random distribution of CaO₁₂ and SrO₁₂ clusters.     

Layered perovskite-related ruthenium oxychlorides: crystal structure of two new compounds Ba5Ru2Cl2O9 and Ba6Ru3Cl2O12

Single crystals of the title compounds were prepared using a BaCl₂ flux and investigated by X-ray diffraction methods using MoKα radiation and a charge coupled device (CCD) detector. The crystal structures of these two new compounds were solved and refined in the hexagonal symmetry with space group P6₃/mmc, a=5.851(1) Å, c=25.009(5) Å, ρ_cal=4.94 g cm⁻³, Z=2 to a final R₁=0.069 for 20 parameters with 312 reflections for Ba₅Ru₂Cl₂O₉ and space group , a=5.815(1) Å, c=14.915(3) Å, ρ_cal=5.28 g cm⁻³, Z=1 to a final R₁=0.039 for 24 parameters with 300 reflections for Ba₆Ru₃Cl₂O₁₂. The structure of Ba₅Ru₂Cl₂O₉ is formed by the periodic stacking along [001] of three hexagonal close-packed BaO₃ layers separated by a double layer of composition Ba₂Cl₂. The BaO₃ stacking creates binuclear face-sharing octahedra units Ru₂O₉ containing Ru(V). The structure of Ba₆Ru₃Cl₂O₁₂ is built up by the periodic stacking along [001] of four hexagonal close-packed BaO₃ layers separated by a double layer of composition Ba₂Cl₂. The ruthenium ions with a mean oxidation degree +4.67 occupy the octahedral interstices formed by the four layers hexagonal perovskite slab and then constitute isolated trinuclear Ru₃O₁₂ units. These two new oxychlorides belong to the family of compounds formulated as [Ba₂Cl₂][Ba_n+1Ru_nO_3n+3], where n represents the thickness of the octahedral string in hexagonal perovskite slabs.     

Switching Ca2+/Ba2+ to Ba2+/Ca2+ Potentiometric Selectivities of Podands with Phosphoryl-containing Terminal Groups: A Molecular Modelling Study

It has been shown experimentally that theCa²⁺/Ba²⁺ potentiometric selectivity ofphosphoryl-containing podandR–-O–-(CH₂–-CH₂–-O)_nndash;-R,R = –-C₆H₄–-P(O)Ph₂, n = 3 (I),switches to Ba²⁺/Ca²⁺ when the ligand containsthe longer polyether chain, n = 5 (II). Here, we reportmolecular dynamics and free energy perturbation simulationsperformed using the amber 4.1 program on the complexesL ^.M²⁺ (M²⁺ = Ca²⁺, Sr²⁺ andBa²⁺, L = I and II) in the gas phase inorder to gain a microscopic insight into structural and energy bindingproperties of podands as a function of n. Mixed QM/MM (PM3/ amber) calculations were performed toanalyse the role of polarisation effects on the complexation selectivityof podands. It isshown that an increase of n does not affect the interactions ofM²⁺ with phosphine oxide groups,but leads to less efficient interactions of small cations with the polyether chain. Calculatedpotentiometric selectivities of I (Ca²⁺ > Ba²⁺)and II (Ba²⁺ > Ca²⁺) are in agreement with the experimental data.     

Das erste Erdalkalimetall-Argentato-Mercurat(II): BaAg2Hg2O4

Summary BaAg₂Hg₂O₄ was prepared by an oxygen high-pressure technique. Single crystal X-ray investigations led to tetragonal symmetry, space group D _4h ³ – P4/nbm;a=6.793;c=7.086 Å;Z=2. Hg²⁺ and Ag⁺ show dumb-bell like coordination by oxygen whereas Ba²⁺ ions are surrounded by 8 O^2– forming distorted cubes. The BaO₈-polyhedra distortions are discussed in respect to the incorporation of Hg²⁺ ions into the BaAg₂O ₄ ^2– network.

     

Structural and magnetic study of the cation-ordered perovskites Ba2−xSrxErMoO6

A series of perovskite phases have been prepared from the appropriate carbonates and oxides by heating under reducing conditions at temperatures up to 1300 °C. Complete ordering between ErO₆ and MoO₆ octahedra and a disordered distribution of Sr²⁺ and Ba²⁺ occur in all compounds. Neutron powder diffraction experiments show that the substitution of Sr²⁺ into Ba₂ErMoO₆ introduces a progressive reduction in symmetry from Fm3¯m (x=0) to I4/m (x=0.5, 0.8) to P2₁/n (x=1.25, 1.75, 2.0). Magnetic susceptibility measurements indicate that all of these compounds show Curie-Weiss paramagnetism and that for x<1.25 this behaviour persists down to 2 K. The monoclinically distorted compounds show magnetic transitions at low temperature and neutron diffraction has confirmed the presence of long-range antiferromagnetic order below 2.5 and 4 K in Ba_0.25Sr_1.75ErMoO₆ and Sr₂ErMoO₆, respectively. Ba_0.75Sr_1.25ErMoO₆, Ba_0.25Sr_1.75ErMoO₆ and Sr₂ErMoO₆ do not undergo structural distortion on cooling from room temperature.     

Ba2NiTeO6 – eine neue Verbindung in der Reihe der hexagonalen Perowskite

Ba₂NiTeO₆ — a novel compound in the series of hexagonal perovskites (Ba₂)(¹²)(NiTe)(⁶)O₆ crystallizes in the rhombohedral space group R3 m with a = 5.797 and c = 28.595 Å for the unit cell in the trigonal setting, which contains 6 formula units. The crystal structure was solved by single crystal X-ray diffraction and refined down to R = 2.9%. It can be described by 12 close-packed BaO₃ layers alternating in the sequence hhcchhcc…, with an ordered occupation of the octahedral lattice sites by Ni and Te atoms. Groups of three octahedra, which are connected with one another by common faces, are linked with each other by TeO₆ octahedra via common corners. The central octahedra of these face-linked groups are occupied by Te, the outer ones by Ni. The bonding within the NiO₆ polyhedra is discussed on the basis of the ligand field spectra and compared to similar compounds. It is shown that there can be an appreciable change of the ligand field parameter Δ (30%) even when the Ni — O distances are nearly equal — in contrast to the predictions of the crystal field theory. Effects of this kind are observed under certain structural conditions, when the bonding within the NiO₆ polyhedra is changed indirectly by substitution of atoms with a noble gas configuration (W⁶⁺) by atoms with a d¹⁰-configuration (Te⁶⁺) in the cationic environment of Ni²⁺.     

Structural, spectroscopic and magnetic investigation of the LiFe1−xMnxPO4 (x=0-0.18) solid solution

Different solid state and sol-gel preparations of undoped and Mn substituted cathode material LiFePO₄ are investigated. Li₃PO₄, Fe₂P₂O₇ and Li₄P₂O₇ are detected and quantified by XRPD only in solid state synthesis. In addition, micro-Raman spectra reveal low amount of different iron oxides clusters. EPR data, combined with the results of magnetization measurements, evidence signals from Fe³⁺ ions in maghemite nanoclusters, and in Li₃Fe₂(PO₄)₃. The sol-gel synthesis, showing the lowest amount of impurity phases, seems the most suitable to obtain a promising cathode material. The structural refinement gives new insights into the cation distribution of the Mn doped triphylite structure: (i) about 85% of Mn²⁺ ions substitutes Fe²⁺, the remaining 15% being located on the Li site, thus suggesting a structural disorder also confirmed by EPR and micro-Raman results; (ii) Mn ions on the Li site are responsible for the observed slight cell volume expansion.     

Structures of ordered tungsten- or molybdenum-containing quaternary perovskite oxides

The room temperature crystal structures of six A₂MMoO₆ and A₂MWO₆ ordered double perovskites were determined from X-ray and neutron powder diffraction data. Ba₂MgWO₆ and Ba₂CaMoO₆ both adopt cubic symmetry (space group Fm3?m, tilt system a⁰a⁰a⁰). Ba₂CaWO₆ has nearly the same tolerance factor (t=0.972) as Ba₂CaMoO₆ (t=0.974), yet it surprisingly crystallizes with I4/m symmetry indicative of out-of-phase rotations of the MO₆ octahedra about the c-axis (a⁰a⁰c^?). Sr₂ZnMoO₆ (t=0.979) also adopts I4/m symmetry; whereas, Sr₂ZnWO₆ (t=0.976) crystallizes with monoclinic symmetry (P2₁/n) with out-of-phase octahedral tilting distortions about the a- and b-axes, and in-phase tilting about the c-axis (a^?a^?c⁺). Ca₂CaWO₆ (t=0.867) also has P2₁/n symmetry with large tilting distortions about all three crystallographic axes and distorted CaO₆ octahedra. Analysis of 93 double perovskites and their crystal structures showed that while the type and magnitude of the octahedral tilting distortions are controlled primarily by the tolerance factor, the identity of the A-cation acts as the secondary structure directing factor. When A=Ba²⁺ the boundary between cubic and tetragonal symmetries falls near t=0.97, whereas when A=Sr²⁺ this boundary falls somewhere between t=1.018 and t=0.992.