Sequence of phase transitions in a quasi-one-dimensional β-Na<Subscript>0.33</Subscript>V<Subscript>2</Subscript>O<Subscript>5</Subscript> compound with variable valence

The thermal properties—specific heat, thermal conductivity, and thermal expansion coefficients—of a single crystal of quasi-one-dimensional variable-valence β-Na_0.33V₂O₅ compound were studied. With lowering temperature, it sequentially undergoes the structural (T _S ～ 230 K), charge (T _C ～ 136 K), and magnetic (T _N ～ 22 K) phase transitions. The structural transition at T _S , resulting in the ordering of the Na ions, and the charge ordering at T _C , resulting in the charge redistribution over the positions of V ions, are accompanied by the anomalies in the temperature dependences of all the studied properties. The magnetic ordering at T _N results in the appearance of the canted antiferromagnetic structure and manifests itself only in the anomaly in the temperature dependences of the thermal expansion coefficients.     

Towards the efficient computation of effective properties of microstructured materialsVers le calcul efficace des propriétés effectives de materiaux microstructurés

An algorithm for partially relaxing multiwell energy densities, such as for materials undergoing martensitic phase transitions, is presented here. The detection of the rank-one convex hull, which describes effective properties of such materials, is carried out for the most prominent nontrivial case, namely the so-called T_k-configurations. Despite the fact that the computation of relaxed energies (and with it effective properties) is inherently unstable, we show that the detection of these hulls (T₄-configurations) can be carried out exactly and with high efficiency. This allows in practice for their computation to arbitrary precision. In particular, our approach to detect these hulls is not based on any approximation or grid-like discretization. This makes the approach very different from previous (unstable and computationally expensive) algorithms for the computation of rank-one convex hulls or sequential-lamination algorithms for the simulation of martensitic microstructure. It can be used to improve these algorithms. In cases where there is a strict separation of length scales, these ideas can be integrated at a sub-grid level to macroscopic finite-element computations. The algorithm presented here enables, for the first time, large numbers of tests for T₄-configurations. Stochastic experiments in several space dimensions are reported here. To cite this article: C.-F. Kreiner et al., C. R. Mecanique 332 (2004).     

Definitionen für Fachbegriffe im Bereich der Diffusion im festen Zustand (IUPAC‐Empfehlungen 1999)

Die Übersetzung basiert auf den „Definitions of Terms for Diffusion in the Solid State“ der Commission on High Temperature Materials and Solid State Chemistry der International Union of Pure and Applied Chemistry, veröffentlicht in Pure Appl. Chem. 1999 , 71, 1307–1325. Das Original wurde von M. Kizilyalli (Middle East Technical University, Ankara, Türkei), J. Corish (Trinity College, University of Dublin, Irland) und R. Metselaar (Technische Universiteit Eindhoven, Niederlande) für die Veröffentlichung vorbereitet.     

Synthesis and Reactions of New Dithiolopyrroles

The title compounds were prepared starting from pyrrolinone 4 . Nucleophilic‐displacement and ring‐closure reactions yielded the dithiolopyrrole 5a , which formed salts with electrophiles ( 7, 8 ) as well as with bases. The crystal structure of 5a was determined. Oxidation of the dithioles 5a and 6a led to S(2)‐oxides ( 10a, 11a ) and the corresponding S(2)‐dioxides ( 10b, 11b ) depending on reaction conditions. The thiosulfinate 10a was converted by a ring‐opening/ring‐closure reaction sequence to the bicyclic sulfinamide 12 . The oxidative addition reactions of [Pt(η²‐C₂H₄) (PPh₃)₂] ( 14 ) with the disulfides 5a and 13 led to the dithiolatoplatinum(II) complexes 15 and 16 , respectively. Complex 16 was characterized structurally. The sulfenato‐thiolato complex 17 was synthesized via reaction of 14 with the thiosulfinate 10a . The thiosulfonato Pt^II complex 18 was prepared by an oxidative insertion of Pt⁰ into the C? S bond of the corresponding thiosulfonate 10b . Furthermore, complex 18 was characterized by single‐crystal X‐ray‐diffraction studies.     

Isotype Strukturen einiger Hexaamminmetall(II)-halogenide von 3d-Metallen: [V(NH3)6]I2, [Cr(NH3)6]I2, [Mn(NH3)6]Cl2, [Fe(NH3)6]Cl2, [Fe(NH3)6]Br2, [Co(NH3)6]Br2 und [Ni(NH3)6]Cl2

The Structures of some Hexaammine Metal(II) Halides of 3 d Metals: [V(NH₃)₆]I₂, [Cr(NH₃)₆]I₂, [Mn(NH₃)₆]Cl₂, [Fe(NH₃)₆]Cl₂, [Fe(NH₃)₆]Br₂, [Co(NH₃)₆]Br₂ and [Ni(NH₃)₆]Cl₂ Crystals of yellow [V(NH₃)₆]I₂ and green [Cr(NH₃)₆]I₂ were obtained by the reaction of VI₂ and CrI₂ with liquid ammonia at room temperature. Colourless crystals of [Mn(NH₃)₆]Cl₂ were obtained from Mn and NH₄Cl in supercritical ammonia. Colourless transparent crystals of [Fe(NH₃)₆]Cl₂ and [Fe(NH₃)₆]Br₂ were obtained by the reaction of FeCl₂ and FeBr₂ with supercritical ammonia at 400°C. Under the same conditions orange crystals of [Co(NH₃)₆]Br₂ were obtained from [Co₂(NH₂)₃(NH₃)₆]Br₃. Purple crystals of [Ni(NH₃)₆]Cl₂ were obtained by the reaction of NiCl₂ · 6H₂O and NH₄Cl with aqueous NH₃ solution. The structures of the isotypic compounds (Fm3 m, Z = 4) were determined from single crystal diffractometer data (see “Inhaltsübersicht”). All compounds crystallize in the K₂[PtCl₆] structure type. In these compounds the metal ions have high-spin configuration. The orientation of the dynamically disordered hydrogen atoms of the ammonia ligands is discussed.     

Synthese und Kristallstruktur von Mangan(II)‐ und Zinkamid,Mn(NH2)2 und Zn(NH2)2

Synthesis and Crystal Structure of Manganese(II) and Zinc Amides, Mn(NH₂)₂ and Zn(NH₂)₂ Metal powders of manganese resp. zinc react with supercritical ammonia in autoclaves in the presence of a mineralizer Na₂Mn(NH₂)₄ resp. Na₂Zn(NH₂)₄_.0.5NH₃ to well crystallized ruby‐red Mn(NH₂)₂ (p(NH₃) = 100 bar, T = 130°C, 10 d) resp. colourless Zn(NH₂)₂ (p(NH₃) = 3.8 kbar, T = 250°C, 60 d). The structures including all H‐positions were solved by x‐ray single crystal data: Mn(NH₂)₂: I4₁/acd, Z = 32, a = 10.185(6) Å, c = 20.349(7) Å, N(F_o) with F > 3σ (F) = 313, N(parameter) = 45, R/R_w = 0.038/0.043. Zn(NH₂)₂: I4₁/acd, Z = 32, a = 9.973(3) Å, c = 19.644(5) Å, N(F_o) with F > 3σ (F) = 489, N(parameter) = 45, R/R_w = 0.038/0.043. Both compounds crystallize isotypic with Mg(NH₂)₂ [1] resp. Be(NH₂)₂ [2]. Nitrogen of the amide ions is distorted cubic close packed. One quarter of tetrahedral voids is occupied by Mn²⁺‐ resp. Zn²⁺‐ions in such an ordered way that units M₄(NH₂)₆(NH₂)_4/2 occur. The H‐atoms of the anions have such an orientation that the distance to neighboured cations is optimum.