Darstellung und Kristallstruktur der Phasen Li26Na58Ba38Ex (E = N,H; x = 0 – 1)

Preparation and Crystal Structures of Li₂₆Na₅₈Ba₃₈E_x Phases (E = N, H; x = 0 – 1) Li₂₆Na₅₈Ba₃₈E_x (E = N, H; x = 0–1) were prepared as a majority phase by the reactions of the metals with Ba(N₃)₂ or BaH₂ at 250 °C for five days. According to single crystal and powder X‐ray diffraction investigation, all compounds are cubic, space group with the unit cell parameter a ranging from 27.335(2) (x = 0) to 27.554(3) (x = 1, E = N, H) Å and Z = 4. This compound series can be described as a filled variant of Li₁₃Na₂₉Ba₁₉, in which nitrogen or hydrogen atoms are found in the centre of Li₂₆ clusters in tetrahedral environment. Li₂₆Na₅₈Ba₃₈E_x represents a new group of metal‐rich compounds extending the growing family of subnitrides.     

Die Seltenerdmetallpolyselenide Gd8Se15, Tb8Se15−x,Dy8Se15−x,Ho8Se15−x,Er8Se15−x und Y8Se15−x (0 < x ≤ 0.3) – Zunehmende Fehlordnung in ausgedünnten,planaren Selenschichten

The Rare Earth Metal Polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x – Increasing Disorder in Defective Planar Selenium Layers Single crystals of the rare earth metal polyselenides Gd₈Se₁₅, Tb₈Se_15?x, Dy₈Se_15?x, Ho₈Se_15?x, Er₈Se_15?x, and Y₈Se_15?x (0 < x ≤ 0.3) have been prepared by chemical transport reactions (1120 K→ 970 K, 14 days, I₂ as carrier) starting from pre‐annealed powders of nominal compositions between LnSe₂ and LnSe_1.9. The isostructural title compounds adopt a 3 × 4 × 2 superstructure of the ZrSSi type and can be described in space group Amm2 with lattice parameters of a = 12.161(1) Å, b = 16.212(2) Å and c = 16.631(2) Å (Gd₈Se₁₅), a = 12.094(2) Å, b = 16.123(2) Å and c = 16.550(2) Å (Tb₈Se_15?x), a = 12.036(2) Å, b = 16.060(2) Å and c = 16.475(2) Å (Dy₈Se_15?x), a = 11.993(2) Å, b = 15.999(2) Å and c = 16.471(2) Å (Ho₈Se_15?x), a = 11.908(2) Å, b = 15.921(2) Å and c = 16.428(2) Å (Er₈Se_15?x), and a = 12.045(2) Å, b = 16.072(3) Å and c = 16.626(3) Å (Y₈Se_15?x), respectively. The structure consists of puckered [LnSe] double slabs and planar Se layers alternating along [001]. The planar Se layers contain a disordered arrangement of dimers, Se^2? and vacancies. All compounds are semiconducting and contain trivalent rare earth metals (Ln³⁺).     

Synthese und Kristallstrukturen von α‐ und β‐Ba3(PS4)2 sowie von Ba3(PSe4)2

Synthesis and Crystal Structures of α‐, β‐Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ Ba₃(PS₄)₂ and Ba₃(PSe₄)₂ were prepared by heating mixtures of the elements at 800 °C for 25 h. Both compounds were investigated by single crystal X‐ray methods. The thiophosphate is dimorphic and undergoes a displacive phase transition at about 75 °C. Both modifications crystallize in new structure types. In the room temperature phase (α‐Ba₃(PS₄)₂: P2₁/a; a = 11.649(3), b = 6.610(1), c = 17.299(2) Å, β = 90.26(3)°; Z = 4) three crystallographically independent Ba atoms are surrounded by ten sulfur atoms forming distorted polyhedra. The arrangement of the PS₄ tetrahedra, isolated from each other, is comparable with the formation of the SO₄^2? ions of β‐K₂SO₄. In β‐Ba₃(PS₄)₂ (C2/m; a = 11.597(2), b = 6.727(1), c = 8.704(2) Å; β = 90.00(3)°; Z = 2) the PS₄ tetrahedra are no more tilted along [001], but oriented parallel to each other inducing less distorted tetrahedra and polyhedra around the Ba atoms, respectively. Ba₃(PSe₄)₂ (P2₁/a; a = 12.282(2), b = 6.906(1), c = 18.061(4) Å; β = 90.23(3)°; Z = 4) is isotypic to α‐Ba₃(PS₄)₂ and no phase transition could be detected up to about 550 °C.     

Quaternary Germanides Formed in Molten Aluminum: Tb2NiAl4Ge2 and Ce2NiAl6‐xGe4‐y (x ∼ 0.24, y ∼ 1.34)

The intermetallic phases Tb₂NiAl₄Ge₂ and Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) were synthesized in molten Al at temperatures below 1000 °C. Both compounds adopt the tetragonal space group I4/mmm with cell parameters of a= 4.1346(2) Å c = 19.3437(7) Å for Tb₂NiAl₄Ge₂ and a= 4.1951(9) Å and c = 26.524(7) Å for Ce₂NiAl_6‐xGe_4‐y. The Tb₂NiAl₄Ge₂ structure features NiAl₄Ge₂ layers separated by a double layer of rare earth ions. The Ce₂NiAl_6‐xGe_4‐y (x ∼ 0.24, y ∼ 1.34) structure also contains the NiAl₄Ge₂ layers along with a vacancy defect PbO‐type Al_2‐xGe_2‐y layer, and is related to the Ce₂NiGa₁₀ structure type. Ordering of vacancies cause the formation of a 3ax3b superstructure in the crystal as seen by electron diffraction experiments. Tb₂NiAl₄Ge₂ exhibits Curie‐Weiss paramagnetic behavior with an antiferromagnetic transition observed at ∼20 K. Ce₂NiAl_6‐xGe_4‐y shows a much more complex magnetic behavior possibly due to temperature induced variation in the valency of the Ce atoms.     

Ba6(MN4)N2–x (M = MoVI/TaV), a Subvalent Nitridometalate with Perovskite‐like Crystal Structure

The subvalent nitridometalate Ba₆[(Mo_1–xTa_x)N₄]N_0.86 was prepared from mixtures of Mo powder with Ba, Na, and Ba₂N at 600 °C in Ta ampoules. It crystallizes in space group Cmcm with a = 11.672(3), b = 10.177(2) and c = 10.8729(19) Å. Its crystal structure exhibits an orthorhombically distorted Perovskite topology with [Ba₆N] building units forming the ReO₃‐type lattice via common vertices, and the nitridometalate anions occupying half of the available distorted cuboctahedral interstices. [MN₄] anions show statistically mixed occupancy of M by Mo^VI and Ta^V. They show no notable deviation from nitridometalate anions in known ionic nitridomolybdates and ‐tantalates, and the metrics of the [Ba₆N] octahedra correspond to those found in similar subvalent compounds. The nitrogen atom position centering the [Ba₆N] octahedra is underoccupied. Band structure calculations corroborate the subvalent character of the compound and the two individual anionic structural building units.     

Ca(2+)/vacancies and O2-/F- ordering in new oxyfluoride pyrochlores Li(2x)Ca1.5-x square 0.5-xM2O6F (M = Nb,Ta) for 0 < or = x < or = 0.5

New oxyfluorides Li(2x)Ca(1.5-x) square (0.5-x)M2O6F (M = Nb, Ta), belonging to the cubic pyrochlore structural type (Z = 8, a approximately 10.5 angstroms), were synthesized by solid state reaction for 0 < or = x < or = 0.5. XRD data allowed us to determine their structures from single crystals for the two alpha and beta-Ca(1.5) square (0.5)Nb2O6F forms and from powder samples for the others. This characterisation was completed by TEM and solid state 19F NMR experiments. For the Ca(1.5) square (0.5)M2O6F (x = 0) pyrochlore phases, the presence of a double ordering phenomenon is demonstrated, involving on one hand the Ca(2+) ions and the vacancies and on the other hand the oxide and the fluoride anions which are strictly located in the 8b sites of the Fd3m aristotype space group. The Ca(2+) ions/vacancies ordering leads to a reversible phase transition, a (P4(3)32) <--> beta (Fd3m). The 19F NMR study strongly suggests that, in the beta-phases, the fluoride ions are only on average at the centre of the Ca3 square tetrahedron. It shows that slightly different Ca-F distances occuring in alpha-Ca(1.5) square (0.5)Nb2O6F may be related to a more difficult thermal ionic and vacancies diffusion process than in the tantalate compound. This may explain the hysteresis phenomenon presented by the phase transition. A solid solution Li(2x)Ca(1.5-x) square (0.5-x) Ta2O6F (0 < or = x < or = 0.5) was prepared and the order-disorder phase transition observed for Ca(1.5) square (0.5)M2MO6F compounds disappears for all the other compositions where less or no more vacancies exist in the 16d sites. In the LiCaM2O6F compounds, the 19F NMR study allows us to determine the Ca(2+) and Li+ ions distributions around the fluoride ions and shows that the [FLi2Ca2] environment is clearly favoured.     

Präparation und Strukturanalyse der Verbindungen Ba2Pb4F10Br2–xIx (x = 0–2) mit verwandten kristallchemischen Motiven aus der Fluoritund Matlockitstruktur

Preparation and Structure of the Compounds Ba₂Pb₄F₁₀Br_2–xI_x (x = 0–2) with Related Structure Motifs of the Fluorites and Matlockites Colourless single crystals of Ba₂Pb₄F₁₀Br_2–xI_x (x = 0–2) have been obtained under hydrothermal conditions (T = 250 °C, 10 d), starting from stoichiometric amounts of BaF₂, PbF₂, PbBr₂ and PbI₂. The compounds crystallize in the tetragonal space group P4/nmm (No. 129). A complete miscibility in the region x = 0–2 has been observed. The mixed crystals follow Vegard's rule. For the compounds with the composition Ba₂Pb₄F₁₀Br₂ (a = 5.9501(2) Å, c = 9.6768(10) Å, R[F² > 2σ(F²)] = 0.022, wR(F² all reflections) = 0.059), Ba₂Pb₄F₁₀Br_1.1I_0,9 (a = 5.9899(3) Å, c = 9.7848(5) Å, R[F² > 2σ(F²)] = 0.014, wR(F² all reflections) = 0.035) and Ba₂Pb₄F₁₀I₂ (a = 6.6417(3) Å, c = 9.9216(10) Å, R[F² > 2σ(F²)] = 0.023, wR(F² all reflections) = 0.049) complete structure analyses have been performed on the basis of single crystal diffractometer data. Microcrystalline single phase compounds Ba₂Pb₄F₁₀Br_2–xI_x (x = 0–2) have been obtained by coprecipitation from aqueous solutions of KF, KBr (KI) and Ba(CH₃COO)₂, Pb(NO₃)₂ in acetic acid medium. For Ba₂Pb₄F₁₀Br_1.5I_0.5 and Ba₂Pb₄F₁₀Br_0.5I_1.5 powder data of microcrystalline samples were used for the Rietveld analyses (R_Bragg = 0.077 for Ba₂Pb₄F₁₀Br_1,5I_0,5 and R_Bragg = 0.065 for Ba₂Pb₄F₁₀Br_0.5I_1.5). The crystal structure comprises alternating structural features of fluorite related type (CaF₂) around Ba and matlockite related type (PbFCl) around Pb1 and Pb2 along the c axis. Barium shows a {8 + 4} cuboctahedral coordination of fluorine. The coordination polyhedron around the two crystallographically independent lead atoms is a monocapped quadratic antiprism built of {4 + 1} fluorine and {4} bromine or iodine atoms, respectively.     

Electrochemical Synthesis of Ba2Ag8S7, a Quasi-One-Dimensional Barium Silver(I) Sulfide Containing Mixed S2−/S22− Ligands

A stingray pattern is adopted by Ba₂Ag₈S₇. Crystals of this compound were grown in a two-electrode chemical cell from a BaS₃/ethylenediamine solution. In the pseudo-one-dimensional structure columns of ¹_∞[Ag₈S₇] (shown in the picture) are stacked head-to-tail to create voids where the barium atoms reside. The coexistence of S²⁻ and S₂²⁻ indicates a reductive decomposition [Eq. (1)].     

Ba3V2O4F8: [V4(O,F)20]8− tetrameric groups of octahedra inserted a tridimensional network of (FBa4) tetrahedra

Ba₃V₂O₄F₈ is prepared by hydrothermal synthesis. The crystal structure is established from single crystal X-ray diffraction data: Space group Pnnm, Z = 4, a = 9.945(4) Å, b = 10.277(1) Å and c = 9.673(1) Å R = 0.0331, R_w = 0.0315 for 892 independent reflections and 86 parameters. The structure is related to that Ba₃Al₂F₁₂ and is described in terms of isolated [V₄(O,F)₂₀]^8? tetrameric groups of octahedra inserted in a tridimensional network of (FBa₄) tetrahedra. Location of oxygen and fluorine atoms is discussed with the help of bond valence calculations.     

Ag5Te2Cl1−xBrx (x = 0 – 0.65) and Ag5Te2−ySyCl (y = 0 – 0.3): Variation of Physical Properties in Silver(I) Chalcogenide Halides

The structures, thermal and physical properties of ion conducting polymorphic Ag₅Te₂Cl_1?xBr_x and Ag₅Te_2?ySyCl have been investigated. A maximum substitution degree of x = 0.65 and y = 0.3 was derived from X‐ray powder diffraction. Mixtures of silver halides, silver chalcogenides and Ag₃TeBr were observed for higher substitution degrees. Both silver chalcogenide halide systems show a Vegard type behaviour. Single crystal structure determinations of selected materials were performed at different temperatures to analyse the silver distribution in the tetragonal high temperature α‐ and the monoclinic room temperature β‐phases. After non‐harmonic refinement of the silver positions detailed joint probability density function analysis (jpdf) and determination of one particle potentials (opp) were carried out to investigate the diffusion pathways and bottlenecks of ion transport for those materials. A preferred anisotropic ion transport along the diffusion pathways for the α‐ and 1D zig‐zag diffusion pathways for the β‐phases were found. α–β and β‐γ phase transitions were determined by DSC and DTA methods and conductivities were measured using temperature dependent impedance spectroscopy. The substitution of tellurium by sulphur lowered the α–β phase transition from 334 K (Ag₅Te₂Cl) to 270 K (Ag₅Te_1.8S_0.2Cl) while the opposite trend was found for the Ag₅Te₂Cl_1?xBrx phases. The α–β phase transition of Ag₅Te₂Cl_0.35Br_0.65 at 343 K represents the highest transition observed for the silver chalcogenide halides under discussion. Total conductivities of approx. 1 Ω^?1 cm^?1 (α‐Ag₅Te₂Cl_0.5Br_0.5) and 0.24 Ω^?1 cm^?1 (α‐Ag₅Te_1.8S_0.2Cl) at 473 K were found being slightly higher (Br) and lower (S) than the conductivity observed for α‐Ag₅Te₂Cl. A conductivity jump of more than two orders of magnitude, related to the α–β phase transitions, within the temperature range from 270 to 343 K is adjustable by simple variation of the composition and is therefore an extraordinary feature of these materials. The total conductivity is linearly correlated to the volume of the anion substructure and can be varied within more than half an order of magnitude.     

Ein Beitrag Über die Verbindung CaBeNd2O5 und Phasen der Zusammensetzung M1−xM′xBeLn2O5 (M = Ca,Ba; M′ = Sr; x = 0,5)

A Contribution on the Compound CaBeNd₂O₅ and Phases of the Composition M_1?xM_x'BeLn₂O₅ (M = Ca, Ba; M′ = Sr; x = 0.5). CaBeNd₂O₅ and the phases (I): Ba_0,5Sr_0,5BeLa₂O₅ and (II): Ca_0,5Sr_0,5BeDy₂O₅ have been prepared by high temperature reactions using a CO₂-LASER. They crystallize with orthorhombic symmetry, space group D-Pnma, CaBeNd₂O₅: a = 9.448(1), b = 7.155(1), c = 6.483(1) Å; (I) a = 9.821(4), b = 7.436(3), c = 6.734(3) Å; (II): a = 9.352(2), b = 7.016(2), c = 6.375(2) Å; Z = 4, and belong to the isotypic series CaBeLn₂O₅ and SrBeLn₂O₅. Calculations of Coulomb energies of ordered BaBeLn₂O₅ and EuBeLn₂O₅ and disordered CaBeLn₂O₅, SrBeLn₂O₅ and EuBeNd₂O₅ show dependencies of the ionic radii of the M²⁺ and Ln³⁺ ions as well as of the order/disorder state.     

Barium‐deficient celsian,Ba1−xAl2−2xSi2+2xO8 (x = 0.20 or 0.06)

Barium‐deficient forms of celsian (barium aluminium silicate) with the formula Ba_1−xAl_2−2xSi_2+2xO₈ (x = 0.20 and 0.06) have been identified. In contrast with the celsian–orthoclase solid solutions which have been reported previously, these forms, refined in the space group C2/m, with Ba and one O atom in the 4i sites with m site symmetry, and a further O atom in a 4g site with twofold axial symmetry, suggest a slight solid solution with silica. The serendipitous preparation of the compounds represents a possible hazard associated with solid‐state synthesis.     

Influence of a Second Cation (M = Ca2+, Mg2+) on the Phase Evolution of (BaxM1–x)F2 Starting from Amorphous Deposits

A second type of cation (Mg²⁺, Ca²⁺) was introduced into BaF₂ by low‐temperature atomic beam deposition. The structure evolution from low‐temperature (–150 °C) amorphous deposits to high‐temperature (< 1000 °C) annealed crystalline phases was studied by in‐situ transmission electron microscopy and X‐ray diffraction. Amorphous (Ba_0.5, Ca_0.5)F₂ crystallizes in a first step to metastable solid solution phase (fluorite‐type), which then decomposes into the pure phases of CaF₂ and BaF₂ at higher temperature. The crystallization behavior of amorphous (Ba_xMg_1–x)F₂ is completely different. When the Mg/Ba atomic ratio is around 1:1, the mixture transforms to the ternary compound BaMgF₄ at annealing, and no decomposition occurs by further heating up to 1000 °C. When the Ba concentration is below 15 % in atomic ratio (x < 0.15), the mixture forms a solid solution phase (rutile type) with the lattice expanded by +1 % compared to rutile type MgF₂. The difference between the phase evolutions of the two mixture systems is discussed.     

Magnetic Ordering in the Solid Solution CePt1–xPdxAl (x = 0.1–0.8)

In order to investigate the magnetic properties of the solid solution CePt_1–xPd_xAl the individual compounds were synthesized from the elements using an arc furnace. From x = 0–0.8 the solid solution crystallizes in the orthorhombic TiNiSi‐type structure (Pnma, no. 62; a = 721–722, b = 448–453 and c = 778–779 pm) and for x = 0.9 both the TiNiSi‐ as well as the hexagonal ZrNiAl‐type structures were observed. The solid solution exhibits an interesting magnetic behavior as for small values of x ferromagnetic ordering can be found. At higher palladium content this changes towards an antiferromagnetic ordering. Furthermore the solid solution exhibits a spin‐reorientation (meta‐magnetic step) for x = 0.2–0.7.     

Mechanochemical synthesis,structure and properties of lead containing alkaline earth metal fluoride solid solutions MxPb1-xF2 (M = Ca,Sr, Ba)

The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M_xPb_1-xF₂ (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M_0.5Pb_0.5F₂. Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M_xPb_1-xF₂ with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by ¹⁹F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of ¹⁹F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M_0.25Pb_0.75F₂, bearing in mind the much higher conductivity of PbF₂ compared to MF₂.