Anomalous octahedral distortion and multiple phase transitions in the metal-ordered manganite YBaMn2O6

By means of powder X-ray diffraction, powder neutron diffraction and transmission electron microscopy (TEM), we determined the crystal structures of a metal-ordered manganite YBaMn₂O₆ which undergoes successive phase transitions. A high-temperature metallic phase (T_c1=520 K<T) crystallizes in a triclinic P1 with the following unit cell: Z=2, a=5.4948(15) Å, b=5.4920(14) Å, c=7.7174(4) Å, α=89.804(20)°, β=90.173(20)°, γ=91.160(4)°. The MnO₆ octahedral tilting is approximately written as a⁰b⁻c⁻, leading to a significant structural anisotropy within the ab plane. The structure for T_c2<T<T_c1 is a monoclinic P2 (Z=2, a=5.5181(4) Å, b=5.5142(4) Å, c=7.6443(3) Å, β=90.267(4)°) with an a⁻b⁻c⁻ tilting. The structural features suggest a d_x²−y² orbital ordering (OO). Below T_c2=480 K, crystallographically inequivalent two octahedra show distinct volume difference, due to the Mn³⁺/Mn⁴⁺ charge ordering. The TEM study furthermore revealed a unique d_3x²−r²/d_3y²−r² OO with a modified CE structure. It was found that the obtained crystal structures are strongly correlated to the unusual physical properties. In particular, the extremely high temperature at which charge degree of freedom freezes, T_c2, should be caused by the absence of the structural disorder and by heavily distorted MnO₆ octahedra.     

Das Schwingungsspektrum von Ba2ZnTeO6

The Vibrational Spectrum of Ba₂ZnTeO₆ The vibration modes of Ba₂ZnTeO₆ are assigned to TeO₆ octahedra linked by apexes and sharing faces respectively. Both octahedra types show different force constants, bond order, and Te? O distances.     

The effect of octahedral tilting on proton binding sites and transition states in pseudo-cubic perovskite oxides

Proton conducting oxide ceramics have shown potential for use in fuel cell technologies. Understanding the energy pathways for proton conduction could help us design more efficient fuel cell materials. This paper describes how octahedral tilting affects the relative energies of proton binding sites, transition states, and conduction pathways in cubic and pseudo-cubic perovskites. First, the structure for cubic and pseudo-cubic forms of BaTiO(3), BaZrO(3), CaTiO(3), and CaZrO(3), is found. Even when cubic symmetry is enforced, CaTiO(3), and CaZrO(3) exhibit octahedral tilting distortions characteristic of orthorhombic phases while BaTiO(3) and BaZrO(3) remain undistorted. Octahedral tilting gives rise to proton binding sites facilitating inter- and intra-octahedral proton transfer while the proton binding sites of undistorted perovskites facilitate only intra-octahedral proton transfer. The nudged elastic band method is used to find minimum energy paths between the proton binding sites. As distortions increase, inter-octahedral proton transfer barriers decrease while intra-octahedral proton transfer barriers increase. Concurrently, rotational barriers from oxygens facilitating inter-octahedral proton transfer increase while rotational barriers from oxygens facilitating intra-octahedral proton transfer decrease. Intra-octahedral transfer is the rate-limiting step to the lowest energy extended proton conduction pathway in all the perovskites considered.     

Zur Struktur von Ba3SmRu2O9, Ba3SmIrRuO9 und Ba2InIrO6

On the Structure of Ba₃SmRu₂O₉, Ba₃SmIrRuO₉, and Ba₂InIrO₆ The compounds Ba₃SmRu₂O₉, Ba₃SmIrRuO₉, and Ba₂InIrO₆ have a hexagonal BaTiO₃ structure (sequence (hcc)₂) with an ordered cationic distribution. The 6 L stacking polytypes Ba₃BM₂O₉ show an 1:2 order (M₂O₉ double octahedra and BO₆ single groups) and crystallize in the space group P6₃/mmc. The refined, intensity related R′ values are 6.9% (Ba₃SmRu₂O₉) and 6.5% (Ba₃SmIrRuO₉). The 1:1 ordered Ba₂InIrO₆, with InIrO₉ double groups and InO₆^?, IrO₆-single octahedra, belongs to the space group P3 m1; the refined R′ is 7,3%.     

The thermodynamic properties of Ba2SrUO6

The standard enthalpy of formation of crystalline Ba₂SrUO₆ at 298.15 K was determined by reaction calorimetry (-2940.0 ± 8.5 kJ/mol). The heat capacity of the compound was measured over the temperature range 8-330 K by adiabatic vacuum calorimetry. The thermodynamic functions of Ba₂SrUO₆ were calculated. The standard entropy (-558.6 ± 2.1 J/(mol K)) and Gibbs function of formation at 298.15 K (-2773.5 ± 9.0 kJ/mol) were determined.     

Über Perowskite Ba2BBTeVIO6

On Perovskites Ba₂B B Te^VIO₆ Compounds of composition Ba₂BBTe^VIO₆ with B^I = Li, Na; B^III = La, Pr, Nd, Sm, Eu, Gd, Tb, Ho, Yb, Y, In, Sc crystallize in a cubic 1:1 ordered perovskite structure. The vibrational spectroscopic investigations show, that more species of TeO₆ octahedra are present in the lattice.     

The magnetic structure of Ba2MnWO6

Powder neutron diffraction and magnetic measurements have shown that the ordered perovskite Ba₂MnWO₆ is antiferromagnetic with a Néel temperature of 7.5 ± 1°K. Below this temperature, ordering of the second kind occurs, with the Mn moments directed perpendicular to the [111] axis.     

Pb,Sr and Ba calix[6]arene hexacarboxylic acid octahedral complexation: a dramatic effect of dealkylation

Calix[6]arene hexacarboxylic acid binds instantly and with low symmetry to Pb, Sr and Ba. Later a highly symmetric up-down alternating conformation emerges. The solution structures are identical to their p-tert-butylcalix[6]arene hexacarboxylic acid counterparts. With either receptor, an octahedral cage is formed around the metal. The transformation from low to high symmetry however proceeds at significantly faster rates for the de-t-butylated host.     

Fluorine magnetic shielding parameters in the [TiF6]2− octahedral anion

Magnetic shielding tensors of fluorine nuclei in the [TiF₆]²⁻ octahedral anion were measured by¹⁹F NMR. Representative experimental data show them to be independent of the crystal environment of the anion. L. A. Kirenskii Institute of Physics, Siberian Branch, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 68–75, July–August, 1994. Translated by L. Smolina     

Zur Kristallstruktur von Ba3In2O6

About the Crystal Structure of Ba₃In₂O₆ Single crystals of Ba₃In₂O₆ could be prepared by recrystallization of a flux and by solid state reaction in closed platinium tubes, respectively. Ba₃In₂O₆ crystallizes with tetragonal symmetry (space group 14/mmm, a = 4.1868; c = 21.7041 Å, Z = 2). Single crystal X-ray work lead to a crystal structure like La_2-xSr_1+xCu₂O_6-δ therefor Ba₃In₂O₆ is a modified member of the Sr₃Ti₂O₇-Type. The coordinations of Ba²⁺ and In³⁺ are described and the relations to the Sr₃Ti₂O₇-type are discussed.     

Preparation of Ag-loaded octahedral Bi2WO6 photocatalyst and its photocatalytic activity

In this work, an Ag-loaded octahedral Bi₂WO₆ photocatalyst has been successfully prepared by the hydrothermal method and photo deposition method. X-ray diffraction (XRD), energy dispersive analysis of X-ray (EDX), field-emission scanning electron microscopy (FE-SEM) and ultra-violet adsorption spectrum (UV-Vis) were employed for characterization of the composite photocatalyst. Furthermore, two different photocatalysts including the obtained Ag-loaded octahedral Bi₂WO₆ were employed here for photodegradation of model contaminated water of Orange II (OII). Results show that Ag-loaded Bi₂WO₆ photocatalyst exhibits superior photocatalytic properties compared to the undoped Bi₂WO₆. The reasons for improvement in photocatalytic activity of the Ag-loaded octahedral Bi₂WO₆ were also discussed.     

Zur Kenntnis von Ba6Ru2PtO12Cl2

About Ba₆Ru₂PtO₁₂Cl₂ Single crystals of Ba₆Ru₂PtO₁₂Cl₁₂ were prepared by a BaCl₂ flux and investigated by X-ray methods (D? P3 M1; a = 5,805; c = 15.006 Å; Z = 1). The characteristic face shared M₃O₁₂-octahedratriples show an ordered (Ru/Pt/Ru) occupation. Calculation of the Coulomb term of lattice energy support the charge distribution (5⁺/4⁺/5⁺) ions engage three point sites with different coordinations. The connection to other compounds are discussed.     

Zur Kenntnis von Ba2As6O11

Concerning Ba₂As₆O₁₁ Ba₂As₆O₁₁ was prepared by hydrothermal reaction of BaO with As₂O₃ at a temperature of 200°C. An X-ray structural analysis demonstrated that the phase contains highly condensed polyarsenate(III) anions (As₆O₁₁^4?)_n. A zweier double chain structure was observed for the anion, in which the individual chains are bridged to one another by two Ψ-AsO₃ tetrahedra, so that As₁₀O₁₀ rings are formed. The double chains are linked into “double sheets”, perpendicular to the b-axis, through relatively strong secondary O … As bonds with an average length of 2.68 Å.     

Hyperfine interaction in K2Ba[Fe(NO2)6

Magnetic hyperfine splitting observed in the low temperature M?ssbauer spectrum of potassium barium hexanitro ferrate(II), in the absence of any external field, is attributed to the 5T2g state of the central metal atom further split into a ground 5Eg state and a first excited 5B2g state under a distorted octahedral symmetry in contrast to the earlier prediction of 1A1g ground state on the basis of room temperature M?ssbauer spectral and other properties. The central iron atom is coordinated to six nitrito groups (NO2-), having an oxidation state of +2. The temperature dependence of M?ssbauer spectra is explained on the basis of electronic relaxation among the spin-orbit coupled levels of the 5Eg ground state. Various kinds of electronic relaxation mechanisms have been compared to explain the proposed mechanism. The observed temperature dependent spectra with varying internal magnetic field and line width can be explained by simple spin lattice relaxation.     

Single-crystal structure of Cs2Re6S6Br8 rhenium thiobromide with acentric Re6 octahedral cluster units

Cs₂Re₆S₆Br₈ (trigonal, a = 10.001(5) Å, c = 14.676(5) Å) exhibits the same structure as Cs₂Mo₆Cl₈Br₆ and Cs₂Mo₆Br₁₄ that were described in a noncentro-and centrosymmetric space groups, respectively. The structure has been refined in P31c space group from a single crystal of actual composition Cs_1.95(1)Re₆S_5.82(3)Br_8.19(3) close to the cesium-rich end of the solid solution Cs₂Re₆S₆Br₈ — CsRe₆S₅Br₉. The centrosymmetry is respected by almost all the atoms of the asymmetric unit, but it is clearly broken by significant differences in the S/Br statistical distribution of the disordered “inner” ligands around the Re₆ cluster. Structural refinements from data collected at 100 K revealed that the Cs cation disorder is static. From the structure refinements, the stable isomers of the [Re₆S₆Br₂] and [Re₆S₅Br₃] cluster cores have been unambiguously determined.     

Strukturbestimmungen an geordneten Perowskiten des Typs Ba2BMVIO6

Determination of Structures of Ordered Perovskites of the Ba₂B M^VIO₆ Type Intensity calculations on powder patterns of Ba₂Y□_0.33M^VIO₆ with M^VI = U, W, Te und Ba₂Gd_0.67□_0.33UO₆ lead for the space group Fm3m/O with 8 Ba in 8c, 8/3 B^III and 4/3 □ in 4b, 4 M^VI in 4a and 24 O in 24e to R values between 4.3 and 7.6%. Two further models are discussed.     

Das Schwingungsspektrum von Ba5(ReO6)2

The infrared and laser-Raman spectra of crystalline Ba₅(ReO₆)₂ are reported and discussed. From the obtained spectroscopic data a calculation of force constants and mean amplitudes of vibration for the ReO₆ ^5– ion has been carried out.

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