Magnetic Investigations and 151Eu Mössbauer Spectroscopy of MYbSi4N7 with M = Sr,Ba, Eu

The isotypic nitridosilicates MYb[Si₄N₇] (M = Sr, Ba, Eu) were obtained by the reaction of the respective metals with Si(NH)₂ in a radiofrequency furnace below 1600 °C. On the basis of powder diffraction data of MYb[Si₄N₇] Rietveld refinements of the lattice constants were performed; these confirmed the previously published single‐crystal data. The compounds contain a condensed network of corner‐sharing [N(SiN₃)₄] units. The central nitrogen thus exhibits ammonium character. Magnetic susceptibility measurements of MYb[Si₄N₇] (M = Sr, Ba, Eu) show paramagnetic behavior with experimental magnetic moments of 3.03(2), (Sr), 2.73(2) (Ba), and 9.17(2) (Eu) μ_B per formula unit. In EuYbSi₄N₇ the europium and ytterbium atoms are in stable divalent and trivalent states, respectively. According to the non‐magnetic character of the alkaline earth cations, ytterbium has to be in an intermediate valence state Yb^III‐x in the strontium and barium compound. Consequently, either a partial exchange N^3—/O^2— resulting in compositions MYb^III‐x[Si₄N_7—xO_x] or an introduction of anion defects according to MYb^III‐x[Si₄N_7—x/3□_x/3] has to be assumed. The phase width 0 ≤ x ≤ 0.4 was estimated according to the magnetic measurements. ¹⁵¹Eu Mössbauer spectra of EuYb[Si₄N₇] at 78 K show a single signal at an isomer shift of δ = —12.83(3) mm s^—1 subject to quadrupole splitting of ΔE_Q = 5.7(8) mm s^—1, compatible with purely divalent europium.     

Thermoanalytical study of the formation of compounds in the PbO−MO (M=Ca,Sr, Ca+Sr) system

In order to clarify the effect of PbO addition on the formation steps of the superconducting phases in the system Bi₂O₃?SrO?CaO?CuO, a study of solid-state reactions under non-isothermal conditions, in the PbO?MO (M=Ca, Sr, Ca+Sr) system has been carried out. Results suggest that the reactivity of the components in the system containing PbO and CaO is much higher than in the system containing SrO. The Ca₂PbO₄ compound is formed first even in the system whereM=Ca+Sr. It is confirmed that Ca₂PbO₄ systems containing PbO.     

Crystal structures of disordered A2Mn3+M5+O6 (A=Sr,Ca; M=Sb,Nb, Ru) perovskites

Polycrystalline samples of A₂MnMO₆ (A=Sr, Ca; M=Nb, Sb, Ru) were prepared by conventional solid state synthesis and their crystal structures were determined using neutron powder diffraction data. All six compounds can be classified as distorted, disordered perovskites. The Mn³⁺/M⁵⁺ distribution is disordered in all six compounds. The strontium containing compounds, Sr₂MnMO₆ (M=Nb, Sb, Ru), undergo out of phase rotations of the octahedra about the c-axis (tilt system a⁰a⁰c⁻) leading to tetragonal I4/mcm space group symmetry. The calcium containing compounds, Ca₂MnMO₆ (M=Nb, Ru, Sb), have orthorhombic Pnma space group symmetry, as a result of a GdFeO₃-type octahedral tilting distortion (tilt system a⁻b⁺a⁻). A cooperative Jahn–Teller distortion is observed in Sr₂MnSbO₆ and Sr₂MnRuO₆, but it is much smaller than the distortion observed in LnMnO₃ (Ln=lanthanide ion) perovskites. It is possible that Jahn–Teller distortions of the MnO₆ octahedra take place on a short-range length scale in the other four compounds, but there is little or no evidence for cooperative ordering of the local distortions. These findings demonstrate a link between orbital ordering, cation ordering and octahedral tilting.     

Synthesis and crystal structure of the alkaline-earth thallates MnTl2O3+n (M=Ca,Sr)

The phases present in the Tl₂O₃–MO system, where M=Ca and Sr, have been synthesised and characterised using powder neutron diffraction data. The structures of the phases known to exist in the Ca_nTl₂O_3+n system with n=1, 1.5, 2 and 3 have been refined and the oxycarbonate phase with composition Ca₄Tl₂O₆CO₃ has been identified. In the Sr_nTl₂O_3+n system, the structures of the phases with n=1, 2 and 3 have also been refined. The M_nTl₂O_3+n phases with M=Ca and Sr and n=1–3 are related to the lillianite structure while the n=4 compound is an oxycarbonate that has been found to crystallise in I4/mmm symmetry for M=Ca and in three different modifications with space groups P4/mmm, I4/mmm and Pmmm for M=Sr, depending on the ordering of the carbonate groups. The relationships between these structures are discussed and comparisons are made to the previously published structures determined from X-ray powder diffraction data.     

Nature of the structural distortion and of the chemical bonding in SnM3Rh4Sn12 (M = LaGd,Yb, Ca,Sr, and Th)

The crystal structure of all the Sn(1)M₃Rh₄Sn(2)₁₂ compounds (M = LaGd, Yb, Ca, Sr, and Tb) have been refined from single crystal X-ray diffraction data. Although the compounds with M = La, Ce, Pr, Nd, Sm and Gd have the phase I′ structure the refinements have been carried out by the use of the phase I unit cell. The only significant difference between the two sets of structures lies in the thermal ellipsoid of the Sn(2) atoms. With the exception of the Th compound the major axis of the Sn(2) thermal ellipsoid is on the average 0.06 Å longer for the structures of phase I′ than for those of phase I. The structure of the Th compound exhibits the longest major axis for the Sn(2) thermal ellipsoid, it must contain thus the phase I′ distortion. The absence of the superstructure spots can be explained by a structural disorder. This anomalously long axis has been interpreted as due to a static displacement of the Sn(2) atoms along the Sn(1)Sn(2) bonds. The distortion from phase I to phase I′ consists thus in a loss of point symmetry of the Sn(1)Sn(2)₁₂ polyhedra. A detailed analysis of the variation of the interatomic distances across the series shows that the chemical bonds in these compounds have a covalent/metallic-metallic character as the second-nearest-neighbor interactions are rather strong. However, an electron transfer takes place in these compounds indicating that the bonds have also an appreciable ionic character. The loss of symmetry which takes place when going from phase I to phase I′ is accompanied by a loss of ionic character of the Sn(1)Sn(2)₁₂ polyhedra. The Eu²⁺ and Yb²⁺ compounds contain some appreciable amount of Eu³⁺ and Yb³⁺ cations, respectively.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0?x?0.4, 0?y?0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

Synthese und XPS-Analyse von nano-skaligen Metall/Metalloxid-Kompositen mit Germanium,Zinn und Blei als metallische Komponente

Synthesis and XPS Analysis of nano-scaled Metal/Metaloxid Composites with Germanium, Tin, and Lead as Metallic Component tert-Butanolates of Germanium(II), tin(II), and lead(II) of the formula {M[O-C(CH₃)₃]₂}_n (M ? Ge, n = 2; M ? Sn, n = 2; M ? Pb, n = 3) as well as the corresponding heterometalalkoxides M′M₂[O? C(CH₃)₃]₆ (M ? Ge, M′ ? Sr, Ba; M ? Sn, M′ ? Ca, Sr, Ba; M ? Pb, M′ ? Ca, Ba) have been subject to a single precursor chemical vapour deposition (CVD) process. In this process the volatile precursor has been pyrolized under reduced pressure (0,1 Torr) on a graphit or metal substrate which has been heated by induction in a microwave field to about 300–500°C. The gases originating from this pyrolisis have been analyzed by means of a quadrupole mass spectrometer whereas the solid coating which contained the micro composite was characterized by X-ray diffraction, electron microscopy, EDX-analysis and XPS-spectra. In all cases the solid material contained two phases, in which the element M ((Ge), Sn, Pb) either had oxidation state 0 or +4 (in the surface of the solids made of germanium containing precursors only Ge^II along with Ge⁰ has been detected by XPS spectroscopy). The group 14-element in the starting material had thus undergone a disproportionation from the +2 oxidation state into a lower and a higher one by two units. The elemental phase and the phase containing the formal +4 cation which is amorphous in most cases and which approaches the formula MO₂ or M′MO³ (M ? (Ge), Sn, Pb; M′ ? Ca, Sr, Ba) are uniformally distributed. The composites consist of ball shaped particles on which other smaller particles are placed in a fractal manner ressembling a black berry. In the case of the composite Sn · BaSnO³ the center of the ball shaped particles has been analyzed as pure elemental tin. The organic substituents of the precursors as well as the dynamic vacuum in the decomposition process seem to be responsible for the ball shaped nature of the solid material. In a test experiment gallium tri-tert-but-oxide has been used as precursor: again ball shaped particles are obtained which have the chemical composition Ga₂O₃ but which contain no elemental gallium.     

Synthese und Kristallstrukturen der Ternären Selten-Erd-Chloride NaMCl4 (M = Eu—Yb,Y)

Synthesis and Crystal Structures of the Ternary Rare Earth Chlorides NaMCl₄ (M = Eu—Yb, Y) Single crystals of NaErCl₄ were obtained from the melt of NaCl and ErCl₃ (1:1 molar ratio) by slow cooling. It crystallizes in the monoclinic crystal system (space group P2/c) with the structure of α-NiWO₄ with a = 632.24(9) pm, b = 759.78(9) pm, c = 674.2(1) pm, b? = 92.310(3)°, Z = 2. Two preparative routes to pure powder samples of the chlorides NaMCl₄ are described. At room temperature, these are found to be isotypic with NaErCl₄ (M = Tm—Yb; II) while the triclinic structure of NaGdCl₄ is adopted with M = Gd—Ho, Y (I). Phase transitions from one structure to the other are observed for all compounds. The transition temperatures decrease with decreasing size of the ion M³⁺.     

Darstellung von Germanium-Mangan-, Germanium-Rhenium- und Zinn-Rhenium-Clustern des Typs M2(CO)8[μ-EXM(CO)5]2, (M = Mn,E = Ge,X = Br,I; M = Re,E = Ge bzw. Sn,X = I bzw. Cl,Br, I)

Preparation of Germanium-Manganese-, Germanium-Rhenium- and Tin-Rhenium-Clusters of the Type M₂(CO)₈[μ-EXM(CO)₅]₂ (M = Mn, E = Ge, X = Br, I; M = Re, E = Ge or Sn, X = I or Cl, Br, I) The clusters Re₂(CO)₈[μ-SnXRe(CO)₅]₂ are prepared by reaction of Re₂(CO)₁₀ and SnX₂ in a Schlenk-tube under release of pressure (X = Cl, Br, I) or in a sealed glass tube (X = Br, I). As central structural unit a four-membered Re₂Sn₂ ring has to be assumed. This unit can be opened again by reaction with CO under pressure. X₂Sn[Re(CO)₅]₂, which is also formed during the preparation of the clusters in dependance of the CO-pressure, indicates insertion of SnX₂ into the Re—Re bond to be the primary step. The corresponding clusters M₂(CO)₈[μ-GeXM(CO)₅]₂ (M = Mn, X = Br, I; M = Re, X = I) are prepared by reaction of GeI₂ and M₂(CO)₁₀ or of I₂Ge[Mn(CO)₅]₂ and Mn₂(CO)₁₀ or of Br₃GeMn(CO)₅ and BrMn(CO)₅. Ir frequencies of the new clusters are assigned.     

Effects of the partial replacement of La by M (M=Ce, Ca and Sr) in La2-xMxCuO4 perovskites on catalysis of the water-gas shift reaction

The performance of La2-xMxCuO4 perovskites (where M = Ce, Ca or Sr) as catalysts for the water-gas shift reaction was investigated at 290 ℃ and 360 ℃. The catalysts were characterized by EDS, XRD, N2 adsorption-desorption, XPS and XANES. The XRD results showed that all the perovskites exhibited a single phase (the presence of perovskite structure), suggesting the incorporation of metals in the perovskite structure. The XPS and XANES results showed the presence of Cu²⁺ on the surface. The perovskites that exhibited the best catalytic performance were La2-xCexCuO4 perovskites, with CO conversions of 85%-90%. Moreover, these perovskites have higher surface areas and larger amounts of Cu on the surface. And Ce has a higher filled energy level than the other metals, increasing the energy of the valence band of Ce and providing more electrons for the reaction. Besides, the La1.80Ca0.20CuO4 perovskite showed a good catalytic performance.     

Phase equilibria and crystal structures of complex oxides in systems La-M-Fe-O (M = Ca or Sr)

Phase equilibria in systems La-M-Fe-O (M = Ca or Sr) at 1100° in air were studied. The homogeneity ranges and structures of solid solutions La_{1 ? x} M _x FeO_{3 ? δ} (0 ≤ x ≤ 0.3 for M = Ca and 0 ≤ x ≤ 0.8 for M = Sr), Sr_{2 ? y} La _y FeO_{4 ? δ} (0.8 ≤ y ≤ 1.0), and Sr_{3 ? z} La _z Fe₂O_{7 ? δ} (0 ≤ z ≤ 0.2) were determined using X-ray powder diffraction. The structural parameters of complex oxides were refined using the full-profile Rietveld technique. Correlations between the unit cell parameters and the compositions of solid solutions were derived. Isobaric/isothermal phase diagrams were constructed for systems La-M-Fe-O (M = Ca or Sr) at 1100°C in air.     

Neue Fluoride MIIIMIVF7 mit MIII = SE,Tl und MIV = Sn,Pb, Pt

New Fluorides M^IIIM^IVF₇ with M^III = SE, Tl and M^IV = Sn, Pb, Pt Colourless Fluorides MSnF₇ (M = La, Sm, Gd, Yb, Lu, Tl), TlPbF₇ and yellow compounds MPtF₇ (M = Eu, Y, Lu) were obtained for the first time either as single crystals or powder samples. They crystallize isostructural to SmZrF₇ (space group P2₁/c-C_2h⁵, Nr. 14; P2₁/n, Z = 4). Crystal data see “Inhaltsübersicht”.     

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.     

Synthesis, structure and dielectric properties of Ba1-xSrxMyTi1-yO3 (M = Zr, Sn)

A series of Ba_1-xSr_xM_yTi_1-yO₃ (M = Zr, Sn, 0⩽x⩽0.4, 0⩽y⩽0.3) solid solutions were synthesized with the soft chemical method below 100 °C. XRD pattern and cell parameters-composition figures of the prepared powder demonstrate that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM shows that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of the powder doped with Sr²+and Zr⁴⁺ or Sn⁴⁺ have dielectric constant eight times higher and dielectric loss thirty per cent lower than those of pure BaTiO₃ phase at room temperature.     

M5(PO4)3F (M=Ca, Sr, Ba)中Sm3+的电荷迁移态及Sm3+和Eu3+的电荷迁移能量关系

采用高温固相反应合成了M_5-2xSm_xNa_x(PO₄)₃F(M=Ca,Sr,Ba)荧光体,研究了其在真空紫外-可见光范围的发光特性。发现在Ca₅(PO₄)₃F中Sm³⁺的电荷迁移带约在191 nm,在Sr₅(PO₄)₃F中约在199 nm,而在Ba₅(PO₄)₃F中约在204 nm,随着被取代碱土离子半径的增大电荷迁移能量逐渐减小。比较了M₅(PO₄)₃F (M=Ca,Sr,Ba)中Sm³⁺和Eu³⁺电荷迁移能量的关系。     

Verbindungsbildung in den quasi-binären Systemen AcX4?MX2 (Ac = Th,U; M = Ca,Sr, Ba,Eu, Ge,Sn, Pb; X = Br,I)

Formation of Compounds in the Quasi-binary Systems AcX₄? MX₂ (Ac = Th, U; M = Ca, Sr, Ba, Eu, Ge, Sn, Pb; X = Br, I) T,x-phase diagrams of the systems ThI₄? SnI₂, ThI₄? PbI₂, ThI₄? CaI₂, and ThI₄? SrI₂ were established using thermoanalysis and x-ray methods. The only ternary compounds have a 1:1 composition. Further AcMX₆ compounds (Ac: Th, U; M: Ca, Sr, Ba, Eu, Ge, Sn, Pb; X: Br, I) were synthesized and their structures investigated. Four structure types are found depending on the temperature and the Ac/M combinations. The structures of γ-ThSnI₆ and β-ThSnI₆ were determined with single crystal methods as representatives of a whole series of isotypic compounds.     

Yb2+3—xPd12—3+xP7 (x = 0.40): Different Ytterbium Species in a Substituted Structural Motif of the Zr2Fe12P7 Type

The new compound Yb_2+3—xPd_12—3+xP₇ x = 0.40(4)) was synthesized by sintering of a mixture of elemental components at 1100 °C with subsequent annealing at 800 °C. The crystal structure of Yb_2+3—xPd_12—3+xP₇ was solved and refined from X‐ray single‐crystal diffraction data: space group P6¯, a = 10.0094(4)Å, c = 3.9543(2)Å, Z = 1; R(F) = 0.022 for 814 observed unique reflections and 38 refined parameters. The atomic arrangement reproduces a structure motif of the hexagonal Zr₂Fe₁₂P₇ type in which one of the transition metal positions is substituted predominantly by ytterbium (Yb : Pd = 0.86(1) : 0.14). The ytterbium atoms are embedded in the 3D polyanion formed by palladium and phosphorus atoms. Two different environments for ytterbium atoms are present in the structure. Magnetic susceptibility measurements and XAS spectroscopy at the Yb L_III edge show the presence of ytterbium in two electronic configurations, 4?¹³ and 4?¹⁴. The following model was derived. Ytterbium atoms in the 3k site are in the 4?¹³ state, the two remaining positions contain ytterbium in intermediate‐valence states, giving totally 79 % ytterbium in the 4?¹³ electronic configuration.     

Etude des systemes CaHPO4−MHPO4−H2O (M=Sr,Ba) A 50°C

The systems CaHPO₄−MHPO₄−H₂O (M=Sr, Ba) were studied at 50°C. ForM=Sr, the series of single phases, Ca_1−xSr_xHPO₄ for 0.95<X<0.75 and Ca_xSr_1−xHPO₄ for 0.4<X<1 have been prepared. These solid solution were caracterized by their infrared spectra and their crystallographic unit cell parameters. ForM=Ba a new phase Ca₂Ba(HPO₄)₃ has been determined. It was characterized by DRX, IR, ATD and chemical analyses.

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Zusammenfassung Bei 50°C wurde das System CaHPO₄−MHPO₄−H₂O (mitM=Sr, Ba) untersucht. FürM=Sr wurden Serien von Einzelphasen erhalten: Ca_1−xSr_xHPO₄ für 0.95<X< 0.75 und Ca_xSr_1−xHPO₄ für 0.4<X<1. Diese Mischkristalle wurden anhand ihrer Infrarotspektren und ihrer kristallographischen Elementarzellenparameter charakterisiert. FürM=Ba wurde die neue Phase Ca₂Ba(HPO₄)₃ ermittelt. Sie wurde mittels DRX, IR, ATD und chemischer Analyse charakterisiert.

     

Study on the equilibrium in the MCl2?CH3OH?H2O System (M = Sr2+, Ba2+) at 25°C and 50°C

Studies on the equilibrium in the system MCl₂? CH₃OH? H₂O at 25°C and 50°C (M = Sr²⁺, Ba²⁺) show that the dehydration in the water-methanol systems proceeds stepwise and all possible lower crystal hydrates may be obtained at 25°C depending on the molar ratio for the mixed solvent. The dehydration and solvation processes in the three-component system MCl₂? CH₃OH? H₂O (M = Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺) have been considered in general and compared with those in the bromide system.