Kristallstrukturuntersuchungen an Verbindungen des Typs A3(M,Nb)8O21 (A  Tl,Ba; M  Fe,Ni)

Crystal Structure Investigations of Compounds with the A₃(M, Nb)₈O₂₁-Type (A ? Tl, Ba; M ? Fe, Ni) Tl₃Fe_0,5Nb_7,5O₂₁ (A), a hitherto unknown phase of the A₃(M, Nb)₈O₂₁-type, and Ba₃Fe₂Nb₆O₂₁ (B), Ba₃Ni_1.33Nb_6,66O₂₁ (C) were prepared and investigated by single crystal X-ray technique. ((A): a = 9.145(1), c = 11.942(1) Å; (B): a = 9.118(2), c = 11.870(1) Å; (C) a = 9.173(3), c = 11.923(1) Å, space group D? P6₃/mcm, Z = 2). There is a statistic occupation of the M-positions by Nb⁵⁺ and Fe³⁺ or Nb⁵⁺ and Ni²⁺, respectively. An other compound Ba₃Fe₂Ta₆O₂₁ is partially ordered in respect to Ta⁵⁺ and Fe³⁺. Calculations of the Coulomb-part of lattice energy are discussed.     

Ba11KX7O2 (X  P,As): Two Novel Zintl Phases with infinite chains of oxygen centered Ba6 octahedra,isolated X3− and dimeric X24− anions

Reactions of “BaX” (X ? P, As) with Ba, K and BaO in tantalum tubes at 900–1000°C yielded black, very air- and moisture-sensitive crystals of Ba₁₁KP₇O₂ and isotypic Ba₁₁KAs₇O₂ which were characterized by EDX and X-ray diffraction (orthorhombic, Fddd, Z = 8; a = 1069.9(1), b = 1514.3(2), c = 3164.6(4) pm and a = 1087.8(2), b = 1542.3(2), c = 3232.4(4) pm, respectively). The structure contains infinite zigzag chains, [Ba₄Ba_2/2O], of oxygen-centered, corner-sharing Ba₆ octahedra along [100]. They are connected by linear strings built of alternating isolated X atoms and X₂ dimers to form layers parallel to (001). While the isolated X atoms are surrounded by eight Ba forming a distorted cube, the X₂ dimers center a Ba₁₂ polyhedron which is comprised of a pair of face-sharing Ba square antiprisms. This results in a cube–antiprism-antiprism-cube sequence of face-sharing Ba polyhedra. Additional X atoms function as spacers between the layers and connect them along [001]. Two atom positions are statistically occupied by Ba and K, and the formula may be written as Ba²⁺₁₁K⁺X^3?₅(X₂)^4?O^2?₂ according to the Zintl-Klemm concept.     

Unexpected Luminescence Properties of Sr0.25Ba0.75Si2O2N2:Eu2+—A Narrow Blue Emitting Oxonitridosilicate with Cation Ordering

Owing to a parity allowed 4f⁶(⁷F)5d¹→4f⁷(⁸S_7/2) transition, powders of the nominal composition Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ (2 mol % Eu²⁺) show surprising intense blue emission (λ_em=472 nm) when excited by UV to blue radiation. Similarly to other phases in the system Sr_1?xBa_xSi₂O₂N₂:Eu²⁺, the described compound is a promising phosphor material for pc‐LED applications as well. The FWHM of the emission band is 37 nm, representing the smallest value found for blue emitting (oxo)nitridosilicates so far. A combination of electron and X‐ray diffraction methods was used to determine the crystal structure of Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺. HRTEM images reveal the intergrowth of nanodomains with SrSi₂O₂N₂ and BaSi₂O₂N₂‐type structures, which leads to pronounced diffuse scattering. Taking into account the intergrowth, the structure of the BaSi₂O₂N₂‐type domains was refined on single‐crystal diffraction data. In contrast to coplanar metal atom layers which are located between layers of condensed SiON₃‐tetrahedra in pure BaSi₂O₂N₂, in Sr_0.25Ba_0.75Si₂O₂N₂:Eu²⁺ corrugated metal atom layers occur. HRTEM image simulations indicate cation ordering in the final structure model, which, in combination with the corrugated metal atom layers, explains the unexpected and excellent luminescence properties.     

Ba6B3+0,5Nb4,5O18 (B ≡ Sc,Y, In,seltene erden): Neue Perowskitvarianten in den systemen BaO-B3+2O3-Nb2O5

In the BaO-B³⁺₂O₃-Nb₂O₅ systems at about 1200 °C with BaO:B₂O₃: Nb₂O₅ ratios of 24:1:9 and B ≡ Sc, In, Lu, Yb, Tm the 18R stacking polytype Ba₆B_0.5Nb_4.5O₁₈ with the sequence hhcccc (space group, R3̄m) is obtained. For B ≡ Er, Ho, Dy there is a small amount of contamination with Ba₅Nb₄O₁₅. With increasing B radius (B ≡ Y, Tb, Gd, Eu) the stability of the 18R-type structure decreases. For B ≡ Sm, Nd no 18R structure formation is observed.     

Zur Kristallchemie der tetragonalen Wolframbronze: Ba6FeNb9O30

Solid state reaction of BaCO₃, FeC₂O₄·2H₂O and Nb₂O₅ gave single crystals of Ba₆FeNb₉O₃₀. The crystal structure was solved by X-ray investigations (a=12.597,c=3.990Å, space group P 4 bm-C _4v ² ,Z=1). Ba₆FeNb₉O₃₀ crystallyzes in the tetragonal bronze type with a statistical distribution of Fe³⁺ and Nb⁵⁺ in the octahedral framework. The anisotropic temperature factors of barium are discussed with respect to the oxygen coordination.

     

New high permittivity tetragonal tungsten bronze dielectrics Ba2LaMNb4O15: M=Mn, Fe

The new phases Ba₂LaMNb₄O₁₅: M=Mn, Fe were prepared by solid state reaction at 1100 °C. They have the tetragonal tungsten bronze structure, space group P4/mbm, at room temperature. The two octahedral sites show partial order of M and Nb with preferential occupancy of the smaller B(1) sites by M. Both phases have high permittivities 90±15 over the range 10-320 K. Ba₂LaFeNb₄O₁₅ is highly insulating with bulk conductivity ?10⁻⁸ ohm⁻¹ cm⁻¹ at 25 °C and tan δ?0.001 over the range 100-320 K and at 10⁵ Hz. Solid solutions between these new phases and the compositionally and structurally related relaxor ferroelectric Ba₂LaTi₂Nb₃O₁₅ show gradual loss of ferroelectric behaviour attributed to replacement of polarisable Ti⁴⁺ by a mixture of (Mn, Fe)³⁺ and Nb⁵⁺.     

Über Geordnete Perowskite mit Kationenfehlstellen. II. Der Ersatz von UVI durch NbV in Ba2Gd0,67□0,33UO6

On Ordered Perovskites with Cationic Vacancies. II. The Incorporation of Nb^V in Ba₂Gd_0,67□_0,33UO₆ In Ba₂Gd_0.67□_0.33UO₆ a complete substitution of U^VI by Nb^V is possible by filling the cationic vacancies (x-phase: Ba₂Gd_0.67+0.33xU_1?xNb_xO₆). For the y-Phase (Ba₂Gd_0.67U_1?yNb_yO_6?0.5y) solid solutions are formed only for y ? 0.5. The properties of both phases are studied by x-ray and spectroscopic methods. In Ba₂GdNbO₆ – in contrary to the complete ordered Ba₂GdTaO₆ – the order of gadolinium and niobium id partial.     

Untersuchungen zu Bismutseltenerdoxidhalogeniden der Zusammensetzung Bi2SEO4X (X = Cl,Br, I)

Investigations on the Bismuth Rare‐Earth Oxyhalides Bi₂REO₄X (X = Cl, Br, I) Compounds of the composition of Bi₂REO₄X (RE = Y, La–Lu; X = Cl, Br, I) have been prepared by solid state reaction of stoichiometric mixtures of BiOX, Bi₂O₃, and RE₂O₃. They were characterized by X‐ray powder diffraction, IR spectroscopy, mass spectrometry and DTA/TG measurements as well. The crystal structure (tetragonal, P4/mmm, a ≈ 3.9 Å, c ≈ 9 Å) was determined by the Rietveld method. In the structure [M₃O₄]⁺ layers are interleaved by single halogen layers. Rare‐earth and bismuth atoms in Bi₂REO₄X are 8‐coordinated. The structure can be derived from the LiBi₃O₄Cl₂ type structure. The enthalpies of formation are derived from heats of solution. The standard entropies were calculated from low‐temperature measurements of the specific heat capacities.     

Ba6CoNb9O30: Ein neuer Vertreter der tetragonalen Wolframbronzen

Ba₆CoNb₉O₃₀: A New Compound of the Tetragonal Bronze Structure The hitherto unknown compound Ba₆CoNb₉O₃₀ was examined by X-ray single crystal work. (Space group C-P4bm; a = 1258.9; c = 400.9 pm) Co³⁺ and Nb⁵⁺ occupy a special position in an octahedral framework. The coordination of Ba²⁺ is discussed.     

High resolution electron microscopy studies of Ba4Nb14O23

The new compound, Ba₄Nb₁₄O₂₃, has been prepared by heating mixtures of Ba₅Nb₄O₁₅, Nb₂O₅ and Nb at 1 450°C under Ar. Ba₄Nb₁₄O₂₃ has been studied by means of high resolution electron microscopy and X-ray powder diffraction techniques. It has a C-centered orthorhombic unit cell with a=20.782(4), b=12.448(3), c=4.148(1) Å and Z=2. The structure of Ba₄Nb₁₄O₂₃ can be considered as being an intergrowth between BaNbO₃ and NbO. Characteristic building units are triple chains of corner sharing Nb₆ octahedra which are connected via columns of the perovskite type structure to a three dimensional network.     

High-resolution electron microscopy of defects in W4Nb26O77

Several different kinds of planar defects have been observed by means of high-resolution electron microscopy in W₄Nb₂₆O₇₇, such as disordered intergrowth of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ structural slabs, locally ordered intergrowth with a sequence of AABAAB, two separate microdomains of WNb₁₂O₃₃ and W₃Nb₁₄O₄₄ coexisting with W₄Nb₂₆O₇₇ and a complicated intergrowth of W₄Nb₂₆O₇₇, NNb₂O₅, W₃Nb₁₄O₄₄, and Nb₃₁O₇₇F types of structure.     

Zur Präparation und Struktur gemischtvalenter Niob-Wolframoxide der Zusammensetzung (Nb,W)17O47

Preparation and Structure of Niobium Tungsten Oxides (Nb,W)₁₇O₄₇ with Mixed Valency The formal substitution of 2Nb⁵⁺ by Nb⁴⁺ or W⁴⁺, respectively, and W⁶⁺ leads to tungsten niobium oxides (Nb,W)₁₇O₄₇ with mixed valency. The phases Nb_8-nW_9+nO₄₇ with n = 1 to 5 could be obtained by heating (1 250°) mixtures of NbO₂ or WO₂, respectively, with Nb₂O₅ and WO₃. The products crystallize with the structure of Nb₈W₉O₄₇. This is proved by X-ray powder diffraction and transmission electron microscopy. A further decrease of the Nb-content results in two-phase products.     

Über Verbindungen vom Typ Ba3BIIMO9 mit BII  Mg,Ca, Sr,Ba und MV  Nb,Ta

Compounds of the Type Ba₃B^IIM O₉ with B^II ? Mg, Ca, Sr, Ba, and M^V ? Nb, Ta The hexagonal perovskites Ba₃B^IIMO₉ (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 BaTiO₃ type (6 L; sequence (hcc)₂) with an 1:2 order for the B and M ions. Intensity calculations for Ba₃SrNb₂O₉ and Ba₃SrTa₂O₉ gave in the space group P6₃/mmc a refined, intensity related R′ value of 8.4% (Nb) and 9.0% (Ta) respectively. For B^II ? Ba the perovskite Ba₃BaTa₂O₉ has an orthorhombic distorted 6 L structure and forms with Ba₃SrTa₂O₉ a continuous series of mixed crystals (Ba₃Sr_1?xBa_xTa₂O₉). In the system Ba₃Sr_1?xBa_xNb₂O₉ the range of existence of the hexagonal BaTiO₃ type is confined to the Sr richer end. The pure Ba compound possesses a proper structure type (5 L: Ba₅BaNb₃□O_13.5□_1.5).     

Über hexagonale Perowskite mit Kationenfehlstellen. XX. Ba6Nb4Zr□O18 – eine neue Stapelvariante mit rhomboedrischer 18 L-Struktur

On Hexagonal Perovskites with Cationic Vacancies. XX. Ba₆Nb₄Zr□o₁₈ - a New Stacking Polytype with a Rhombohedra1 18 L Structure The white Ba₆Nb₄Zr□O₁₈ crystallizes in a rhombohedral 18 L structure (a = 5.82₁ Å; c = 42.6₃ Å; space group R3 m) with three formula units for the trigonal setting (?_exp = 6.0₅ g/cm³; ?_calc = 6.27₁ g/cm³). The corresponding Ti^IV and Hf^IV compounds, Ba₆Nb₄Zr□O₁₈ and Ba₆Nb₄Hf□O₁₈, are isotypic.     

High n-value phases in the complex bismuth oxides with layered structure,Bi2CaNan−2NbnO3n+3

Complex bismuth oxides with layered structure are prepared with a series of compositions in the system Bi₂CaNb₂O₉-NaNbO₃. It is found by X-ray powder diffraction that each compound is composed of more than two phases, which are described by a formula Bi₂CaNa_n?2Nb_nO_3n+3, e.g., in the sample with the nominal composition Bi₂CaNb₂O₉ · 8NaNbO₃, the phases with n = 6 to 8 appear predominantly. These phases are closely intergrown to each other. Moreover, high-resolution electron microscopy reveals that microsyntactic intergrowth frequently occurs in the phases with n > 5. The occurrence of the latter intergrowth is explained in terms of the bond length obtained.     

Cluster intergrowth of perovskite and defect sodium chloride type structures in the K---Nb---O system: The structure of KNb4O6

A new reduced potassium niobate (KNb₄O₆) of intergrowth type structure containing condensed Nb₆O₁₂ clusters has been found. The structure has been determined from HREM images. The atomic positions have been refined with the Rietveld technique using X-ray powder diffraction data. The space group of KNb₄O₆ is P4/mmm; Z = 1, and its unit cell parameters are a = 4.1393(1) and c = 8.2537(2). KNb₄O₆ consists of alternating slabs of KNbO₃ (perovskite) and NbO (ordered deficient NaCl-type) both being a single unit thick. The structure is closely related to that of A₂Nb₅O₉ (A = Ba, Sr). Both phases can be considered as members (n = 1 and 2 respectively) of a homologous series A_nNb_3+nO_3+3n. Electron microscopy studies show the presence of defects, both as extra perovskite layers and missing NbO slabs, together with areas of more disordered intergrowth. The profile refinement and microanalysis of individual crystal fragments both indicate the structure to be niobium deficient according to the formula K_1+x/2Nb_4−xO₆.     

Synthesis and Crystal Structures of Cs5Nb2S4X9 – Double Salts Containing New Cluster Anions [Nb2(μ-S2)2X8]4– (X = Cl,Br)

Bis(disulfide)bridged Nb(+4) cluster halide complexes [Nb₂S₄X₈]^4– (X = Cl, Br) were prepared by acid hydrolysis of [Nb₂S₄(NCS)₈]^4– in concentrated aqueous HCl or HBr, solution from which they can be isolated as double salts Cs₅[Nb₂S₄X₈]X (X = Cl, 1 ; X = Br, 2 ). The crystal structures of 1 and 2 were determined. The isolation and X-ray structure of oxonium salt (H₃O)₅ [Nb₂S₄Cl₈]Cl ( 3 ) is also reported. 1 – 3 contain new [Nb₂S₄X₈]^4– anions which can also be viewed as excised building blocks of polymeric solids NbS₂X₂. The extra halogen resides in the center of octahedron formed by six Cs⁺ or H₃O⁺ ions. All the three salts are isostructural and crystallize in tetragonal space group Immm with the following parameters: a = 10.269(2), b = 16.343(2), c = 7.220(1) Å for 1 , a = 10.934(1), b = 16.613(2), c = 7.470(1) Å for 2 , a = 9.639(1), b = 16.031(1), c = 7.071(1) Å for 3 . The parameters of the Nb₂S₄ core are only slightly affected by the change from Cl to Br.     

Ba2BiV3O11 mit Bismut in geschlossener Koordination

Ba₂BiV₃O₁₁ containing Bismuth within closed Coordination A new barium bismuth oxovanadate, Ba₂BiV₃O₁₁, was prepared and investigated by X-Ray single crystal technique. It crystallizes with monoclinic symmetry space group C—P2₁/a, lattice constants a = 24.6473; b = 7.7347; c = 5.6375 Å, β = 103.16°; Z = 4. Octahedra arround Bi³⁺, tetrahedra and double tetrahedra arround V⁵⁺ form a tunnel structure. The tunnel positions are occupied by Ba(2).     

Synthesis and Structural Characterization of New Phases in the Cubic M3Te2O6X2 (M = Sr,Ba; X = Cl,Br) Structure Family

Four alkaline earth oxotellurate(IV) halides with common formula M₃Te₂O₆X₂ (M = Sr, Ba; X = Cl, Br) have been prepared as polycrystalline powders and/or in the form of single crystals. All compounds crystallize in the cubic space group Fd$\bar{3}$ m with cell parameters a = 15.9351(4) Å for Sr₃Te₂O₆Cl₂ (single‐crystal X‐ray data), 16.052(5) Å for Sr₃Te₂O₆Br₂ (powder X‐ray data), 16.688(2) Å for Ba₃Te₂O₆Cl₂ (single‐crystal X‐ray data) and 16.8072(3) Å for Ba₃Te₂O₆Br_1.64Cl_0.36 (single‐crystal X‐ray data). The results of the crystal structure analyses reveal a rigid ${3}\atop{{\infty}}$ [M₃Te₂O₆]²⁺ framework which can be described as being composed of regular octahedra of two types of chemically non‐bonded M₆ octahedra that are capped by trigonal pyramidal [TeO₃] anions located above every second face of one of the M₆ octahedra. The halide X^– anions are situated in the voids of the ${3}\atop{{\infty}}$ [M₃Te₂O₆]²⁺ framework. Dependent on the nature of the halogen, the anions show various kinds of occupational disorder which eventually led to a revision of the previous structure model of Ba₃Te₂O₆Cl₂. A comparative discussion with other structures of general formula M₃Ch₂O₆X₂ (M = divalent metal; Ch = Te, Se; X = Cl, Br) is presented.     

Über ternäre Oxocuprate. X. Zur Kenntnis von Ba2Cu3O4Cl2

About Ternary Oxocuprates. X. On Ba₂Cu₃O₄Cl₂ The preparation of Ba₂Cu₃O₄Cl₂ and results by single crystal X-ray methods are described (a = 5.517, c = 13.808 Å; Space group D–I4/mmm). A so far unknown arrangement of square coordinated Cu²⁺ was detected. The Cu²⁺/O^2?-squares are partly completed to a distorted octahedral coordination by two Cl^?.