New germanates RCrGeO5 (R=Nd-Er, Y): Synthesis, structure, and properties

The new complex germanates RCrGeO₅ (R=Nd-Er, Y) have been synthesized and investigated by means of X-ray powder diffraction, electron microscopy, magnetic susceptibility and specific heat measurements. All the compounds are isostructural and crystallize in the orthorhombic symmetry, space group Pbam, and Z=4. The crystal structure of RCrGeO₅, as refined using X-ray powder diffraction data, includes infinite chains built by edge-sharing Cr⁺³O₆ octahedra with two alternating Cr−Cr distances. The chains are combined into a three-dimensional framework by Ge₂O₈ groups consisting of two edge-linked square pyramids oriented in opposite directions. The resulting framework contains pentagonal channels where rare-earth elements are located. Thus, RCrGeO₅ germanates present new examples of RMn₂O₅-type compounds and show ordering of Cr⁺³ and Ge⁺⁴ cations. Electron diffraction as well as high-resolution electron microscopy confirm the structure solution. Magnetic susceptibility data for R=Nd, Sm, and Eu are qualitatively consistent with the presence of isolated 3d (antiferromagnetically coupled Cr⁺³ cations) and 4f (R⁺³) spin subsystems in the RCrGeO₅ compounds. NdCrGeO₅ undergoes long-range magnetic ordering at 2.6 K, while SmCrGeO₅ and EuCrGeO₅ do not show any phase transitions down to 2 K.     

Meson production in p + d reactions

Total and differential cross sections for the reactions p + d → ³He + m ⁰ with m=π, η and p + d → ³H+π⁺ were measured with the GEM detector at COSY for beam momenta between threshold and the maximum of the corresponding baryon resonance. For both reactions a strong forward-backward asymmetry was found. The data were compared with model calculations. The aspect of isospin symmetry breaking is studied. Representing the GEM Collaboration     

Working group report: Heavy-ion physics and quark-gluon plasma

This is the report of Heavy Ion Physics and Quark-Gluon Plasma at WHEPP-09 which was part of Working Group-4. Discussion and work on some aspects of quark-gluon plasma believed to have created in heavy-ion collisions and in early Universe are reported.     

Fluorinated heterometallic β-diketonates as volatile single-source precursors for the synthesis of low-valent mixed-metal fluorides

Hexafluoroacetylacetonates that contain lead and divalent first-row transition metals, PbM(hfac)(4) (M = Ni (1), Co (2), Mn (3), Fe (4), and Zn (5)), have been synthesized. Their heterometallic structures are held together by strong Lewis acid-base interactions between metal atoms and diketonate ligands acting in chelating-bridging fashion. Compounds 1-5 are highly volatile and decompose below 350 °C. Fluorinated heterometallic β-diketonates have been used for the first time as volatile single-source precursors for the preparation of mixed-metal fluorides. Complex fluorides of composition Pb(2)MF(6) have been obtained by decomposition of 1-5 in a two-zone furnace under low-pressure nitrogen flow. Lead-transition metal fluorides conform to orthorhombically distorted Aurivillius-type structure with layers of corner-sharing [MF(6)] octahedra separated by α-PbO-type (Pb(2)F(2)) blocks. Pb(2)NiF(6) and Pb(2)CoF(6) were found to exhibit magnetic ordering below 80 and 43 K, respectively. The ordering is antiferromagnetic, with a weak, uncompensated moment due to the canting of spins. The Pb(2)MF(6) fluorides represent a new class of prospective magnetoelectric materials combining transition metals and lone-pair main-group cations.     

Interaction between explosive and analyte layers in explosive matrix-assisted plasma desorption mass spectrometry

An HMX/insulin two-layer system was chosen as a model for further investigation of the matrix properties of explosive materials for protein analytes in plasma desorption mass spectrometry. The dependencies of the molecular ion yield and average charge state as a function of the analyte thickness were studied. An increase in the charge state of multiply protonated molecular species was confirmed as the major matrix effect, with the average charge state z at the smallest thickness studied being higher than in matrix-assisted laser desorption/ionization and closer to the value obtained in electrospray ionization under standard acidic conditions. Observed charge state distributions are significantly narrower than the corresponding Poisson distributions, which suggests that the protonation of insulin is limited in plasma desorption by the number of basic sites in the molecule, similar to electrospray ionization. Both the curve displaying total molecular ion yield and the one showing the total charge (proton) yield as a function of the insulin thickness have maxima at a thickness different from an insulin monolayer. These observations diminish the significance of a matrix/analyte interface mechanism for the explosive matrix assistance. Instead, a mechanism related to the chemical energy release during conversion of the explosive after the ion impact is proposed. As additional mechanisms, enhanced protonation of the analyte through collisions with products of the explosive decay is considered, as well as electron scavenging by other products, which leads to a higher survival probability of positively charged protein molecular ions. Copyright 1999 John Wiley & Sons, Ltd.     

Pb2.63Cd2V3O12, a cation‐deficient garnet‐type vanadate

In the crystal structure of the cation‐deficient garnet Pb_2.63Cd₂V₃O₁₂ (lead cadmium vanadium oxide), the Cd and V atoms fully occupy octahedral and tetrahedral sites, respectively, whereas the Pb atoms partially occupy a dodecahedral site. The total Pb and Cd content indicates that vanadium is slightly reduced from the +5 oxidation state.     

Crystal structure and thermal stability of Ni151.5Pb24S92. Search for selenium- and tellurium-containing analogs

The crystal structure of the subvalent nickel—lead sulfide, which has been described previously as Ni₆₀Pb₉S₃₁, was established and the composition of this sulfide was refined based on powder X-ray diffraction data. The true Ni_151.5Pb₂₄S₉₂ composition of this compound was confirmed by the EDX techniques. The temperature range of stability of this compound (490—578 °C) was refined by differential thermal analysis. In the search for analogs, the triangulation of the Ni—Pb—Se and Ni—Pb—Te systems at 540 °C was carried out for the first time. No new ternary phases were detected.     

Crystal structure and properties of the new vanadyl(IV)phosphates Na2MVO(PO4)2, M=Ca and Sr

Two new complex vanadyl(IV)phosphates Na₂MVO(PO₄)₂ (M=Ca, Sr) were synthesized in evacuated quartz ampoules and investigated by means of X-ray diffraction, electron microscopy, DTA, ESR and magnetic susceptibility measurements. The crystal structure of Na₂SrVO(PO₄)₂ was solved ab initio from X-ray powder diffraction data. Both compounds are isostructural: a=10.5233(3) Å, b=6.5578(2) Å, c=10.0536(3) Å and a=10.6476(3) Å, b=6.6224(2) Å, c=10.2537(3) Å for Ca and Sr, respectively; S.G. Pnma, Z=4. The compounds have a three-dimensional structure consisting of V⁴⁺O₆ octahedra connected by PO₄ tetrahedra via five of the six vertexes forming a framework with cross-like channels. The strontium and sodium atoms are located in the channels in an ordered manner. Electron diffraction as well as high-resolution electron microscopy confirmed the structure solution. The new vanadylphosphates are Curie-Weiss paramagnets in a wide temperature range down to 2 K with θ=12 and 5 K for Ca and Sr phases, respectively.     

Synthesis and crystal structure of new titanyl phosphate Sr2TiO(PO4)2

New strontium titanyl phosphate Sr₂TiO(PO₄)₂ (1) was synthesized and characterized by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy, and band structure calculations. Titanyl phosphate 1 is isostructural with vanadyl phosphate Sr₂VO(PO₄)₂ and has a layered structure. The titanium atoms are shifted from the centers of the TiO₆ octahedra and form short (1.74 Å) titanyl bonds. The structure of 1 is an unusual example of the disordered orientation of the chains formed by TiO₆ octahedra in complex titanium phosphates.     

Crystal Structure and Magnetic Properties of the Novel Oxide Pb2V5O12

The crystal structure of the new oxide Pb₂V₅O₁₂ was determined from X‐ray single crystal and neutron powder diffraction data. The oxide is monoclinic, space group P2/c with a = 8.408(2), b = 5.017(1), c = 11.940(2) Å, β = 98.42(3)°, Z = 2. The crystal structure of Pb₂V₅O₁₂ consists of isolated layers formed by edge and corner sharing VO₅ square pyramids with short vanadyl bonds directed above and below the layers. Six pyramids linked by corner form so‐called “tiling plaquettes”. Neighboring plaquettes are linked by edge sharing. The Pb cations are located in the interstitial positions between layers. The structure of Pb₂V₅O₁₂ is closely related to the MV O_2n+1 homologous series known for Ca, Sr and Cd. Electron diffraction and high resolution electrom microscopy study confirm the crystal structure data and revealed a phase transition induced by irradiation resulting in the formation of a disordered orthorhombic phase (a ≈ 3.75, b ≈ 3.79, c ≈ 5.03 Å) which corresponds to a sublattice of the plaquette‐built structure. The analyses of related structures allowed to suggest a more general formula for this homologous series: M_mV_m+nO_3m+2n. The structures of such compounds may be described by shear planes formed by a shift of the VO₂ units over a 1/2* [110] translation starting from the parent “VO₂” or “MVO₃” structures. Magnetic susceptibility measurements of Pb₂V₅O₁₂ indicate low dimensional behavior and a strong antiferromagnetic exchange within the plaquettes with J of the order of 190 K. Anomalies observed in the susceptibility and the specific heat indicate magnetic order at T_N = 26 K.