Preparation and properties of the systems Co1−xRhxS2, Co1−xRuxS2, and Rh1−xRuxS2

Members of the systems Co_1−xRh_xS₂ (0 ≤ x ≤ 0.6) were prepared, and their crystallographic and magnetic properties studied. The observed ferromagnetic moments for compositions where x ≤ 0.2 indicate a ferromagnetic alignment between Co(3d⁷) and Rh(4d⁷) electrons. This is the first observation of localized behavior of 4d electrons in the pyrite structure. Members of the systems Co_1−xRu_xS₂ (0 ≤ x ≤ 1) and Rh_1−xRu_xS₂ (0.5 ≤ x ≤ 1) were also prepared and their crystallographic and magnetic properties studied. From comparison with the Co_1−xRh_xS₂ system, it appears that the 4d electrons of Rh(4d⁷) are localized in the presence of Co(3d⁷) but are delocalized in the presence of Ru(4d⁶). The magnetic susceptibility of the Co_1−xRu_xS₂ system is sensitive to the homogeneity of the products and indicates that Ru(4d⁶) behaves as a diamagnetic ion.     

Das Ultrarotspektrum von isotaktischem Polypropylen zwischen 1500 cm−1 und 330 cm−1

Zusammenfassung Die Frequenzen der Skelettschwingungen von isotaktischem Polypropylen werden mit Hilfe des Valenzkraft-Modells berechnet und mit den im UR-Spektrum gemessenen Frequenzen verglichen. Die übereinstimmung ist so gut, da? eine Zuordnung der Banden zu den Molekelschwingungen gegeben werden kann. Dagegen k?nnen die Intensit?tsverh?ltnisse nicht gekl?rt werden. Herrn Professor Dr.Hellwege danke ich für Anregungen und Diskussionen zu dieser Arbeit. Ferner danke ich den Firmen Kalle, Wiesbaden, und Farbwerke Hoechst für die zur Verfügung gestellten Polypropylenproben, der Deutschen Forschungsgemeinschaft für die Bereitstellung des Rechenautomaten und HerrnG. Günther für die Hilfe beim Programmieren.     

Synthesis of Novel Organosiliconsulfur-Containing Tetrasubstituted Imidazoles Sonocatalyzed by LaxSr1−xFeyCo1−yO3 Nanoperovskites

Abstract

The one-pot synthesis of tetrasubstituted imidazoles by use of a series of La_xSr_1 ? xFe_yCo_1 ? yO₃ perovskites as catalysts is described. The La_0.8Sr_0.2Fe_0.34Co_0.66O₃ nanocatalyst had the greatest activity in the heterogeneous cyclocondensation of an aldehyde, benzil, ammonium acetate, and a primary aromatic amine in water under ultrasonic irradiation. Some of the derivatives generated during this work were utilized as substrates for the synthesis in good yields of novel multifunctional tetrasubstituted imidazoles with Me₃Si, C=S, and SH groups, via nucleophilic attack of tris(trimethylsilyl)methyllithium (TsiLi) at the carbon of carbon disulphide.     

Vacancy ordering in Gd1−xSe

Vacancy ordering is observed in the compound Gd_0.88Se. The symmetry is reduced fromFm3m¯ for stoichiometric GdSe toPm3m¯ and the cubic cell edge is 5.7669(4)A˚. The Gd occupancies become of Cu₃Au type, whereas no vacancies or distortions were observed for the Se sublattice.     

Hydrothermal processing and characterization of Ce1−xPbxO2−δ solid solutions

Nanocrystals of Ce_1?xPb_xO_2?δ (x = 0.00, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, and 0.35) were prepared by a hydrothermal reaction route. During the formation reaction, buffer solutions were explored as an effective additive to retain the initial molar ratio. With increasing the Pb²⁺ content, the average crystallite size was slightly retarded. Morphologies observed by transmission electron microscope indicated that the particles were spherical-like and highly uniformed. Pb²⁺ ions are homogenously distributed in the solid solutions. Analyses using X-ray diffraction, Raman and UV spectroscopies showed that the solid solubility limit of Pb²⁺ in CeO₂ was about x = 0.20. For x < 0.20, with increasing the Pb²⁺ content, the bulk conductivity increased, and the oxygen storage capacity was enhanced as followed by a decrease in reduction temperature.     

Mössbauer spectroscopic analysis of Bi1−xSrxFeO3−δ perovskites

Bi_1?xSr_xFeO_3?δ perovskites synthesised by solid-state reaction in ambient atmosphere or in a closed vessel were analysed by X-ray diffraction and Mössbauer spectroscopy. The evolution of the valence state of iron with both Bi/Sr ratio and oxygen content has been more particularly discussed. The samples are single phase and homogeneous for x ≤ 0.5 (Bi-rich) and x > 0.8 (Sr-rich). For intermediate Sr contents, the samples are less homogeneous and tend to contain both Bi-rich and Sr-rich phases. The appearance of Sr-rich phases for x > 0.5 corresponds to the appearance of Fe⁴⁺, to compensate for the lack of positive charges due to the replacement of Bi³⁺ by Sr²⁺.     

Sintering, microstructures and dielectric properties of Ba1−xPbx(Ti1−xLix)O3−3xF3x ferroelectric ceramics

Various compositions (1−x)BaTiO₃ + xPbF2 + xLiF were prepared, shaped to pellets then sintered at 900°C for 2 h in gold sealed tubes. The purity and the symmetry of the obtained samples were checked by X-ray diffraction. A new solid solution with Ba_1−x Pb _x (Ti_1−x Li _x ) O_3−3x F_3x formula occurs in the composition range 0 ≤ x ≤ 0.20. SEM observations were performed on polished and fractured ceramics. The complex permittivity was measured as a function of temperature (−120°C ≤ T ≤ 250°C) and frequency (50 Hz ≤ f ≤ 4 × 10⁷ Hz). The dielectric performances are the best for ceramic Ba_0.97Pb_0.03(Ti_0.97Li_0.03)O_2.91F_0.09. The real component ε′, exhibits a maximum of approximately 7500 at the ferroelectric Curie temperature T _C ≈ -18°C, the dielectric losses tan δ value being 0.012. At room temperature, the relaxation frequency f _r is around 40 MHz for this ceramic. This novel ferroelectric oxifluoride is a promising material for applications, in particular in the field of Z5U multilayer capacitors.      

Defects in doped perovskite-like lanthanum cobaltite crystals La1−x SrxCo1−y MeyO3−δ (Me = Cu and Mn)

The paper presents a thermodynamic analysis of the formation of equilibrium defects in perovskitelike La_1?x Sr_xCo_1?y Me_yO_3?δ oxides, where Me = Cu or Mn, x = 0.0 or 0.3, and y = 0.0, 0.25, or 0.3, at high temperatures (873 K ≤ T ≤ 1373 K) depending on the composition and oxygen pressure (10^?8 atm ≤ $p_{O_2 } $ ≤ 1 atm). The results were used to study the nature of charge transfer. Small-radius polarons were shown to be responsible for the electric properties of the cobaltites under consideration; their concentrations and mobilities were calculated.     

A Mössbauer spectroscopy investigation of SrFe1−xScxO3−δ perovskites

Polycrystalline samples of oxygen deficient perovskites SrFe_1?xSc_xO_3?δ (0 ≤ x ≤ 0.5) have been synthesized by direct solid state reactions. Each compound has been stabilized with two different oxygen stoichiometries. The structural study shows, firstly, the good cationic homogeneity of the samples and, secondly, that the Sc and Fe atoms are randomly distributed over the same crystallographic site, whatever the scandium content. This implies that no anionic order is possible. A detailed Mossbauer spectroscopy study clearly shows that the substitution of scandium for iron involves an oxygen content decrease which decreases the tetravalent iron content until its total disappearance for x = 0.5. The evolutions of the isomer shift, the quadrupolar splitting and the relative intensity versus the Sc³⁺ content are depicted in the present paper.     

Untersuchungen in den Systemen: V−B,Nb−B,V−B−Si und Ta−B−Si

Zusammenfassung Mit Hilfe röntgenographischer Messungen werden die Boride von Vanadin und Niob untersucht, wobei eine neue Phase der ungefähren Zusammensetzung V₂B identifiziert wird, welche mit der entsprechenden Nb-Borid-Phase isotyp ist. Dieselbe Kristallart tritt auch im System: Ta–B auf. Die in der Literatur angegebene -Phase im Zweistoff: Nb–B erweist sich als NbO.Im System: V–B–Si wird wie im analogen Mo-System die Existenz einer ternärenT 2-Phase Me₅(Si_1/3, B_2/3)₃ nach-gewiesen¹; ihre Gitterkonstanten werden ermittelt.Im Schnitt Ta₂Si–Ta₂B besteht ein geringes Lösungs-vermögen der beiden Phasen ineinander. Durch Zusatz von 20 Mol-% Ta₂Si zu Ta₂B erhält man die oben erwähnte neue Kristallart.Bei den Borid-Siliziden der Metalle aus der 4a-, 5a- und 6a-Gruppe werden die Stabilitätsbereiche derT 1-,T 2- undD 8₈-Phasen miteinander verglichen.     

Thermal behaviour of chemically deintercalated Li1−1Ni1+xO2

The thermal behaviour of chemically deintercalated samples obtained by HCl treatment of non-stoichiometric Li/Ni mixed oxides is studied. A multi-step reduction of Ni with O₂ evolution is observed between room temperature and 800C. Two cation redistribution processes are shown by the exothermal occurrence of a spinel phase at 300C and the endothermal reduction to a rock-salt phase with random distribution of Li and Ni cations in octahedral sites at 800C.The authors wish to express their acknowledgement to CICYT and PFPI for financial support.     

Structure,nonstoichiometry and magnetic properties of the perovskites Sr1−xCaxMnO3−δ

The structural, thermal and magnetic properties of the perovskite-type alkaline-earth manganites of the series Sr_1−xCa_xMnO_3−δ (0⩽x⩽1) were investigated. SrMnO_3−δ forms a hexagonal perovskite lattice and shows a first-order transformation to a highly defective cubic high-temperature modification. By substituting Ca for Sr (x>0.25) the hexagonal perovskite is suppressed and a cubic (or orthorhombic) lattice becomes stabilized for all temperatures. For x=0.5 and 0.75 cubic perovskites with a large nonstoichiometry (e.g., δ=0.25 for x=0.5) are obtained at 1400 °C. The defective perovskites are prepared by either quenching from high temperature or by cooling in an inert atmosphere. The oxygen vacancies are easily filled by subsequent reoxidation at low temperature (400–600 °C) and stoichiometric samples are obtained. Orthorhombic perovskites are formed at T⩽1200 °C with the nonstoichiometry δ increasing with increasing temperature (e.g., δ=0.06 at 1000 °C and δ=0.14 at 1200 °C for x=0.5). Slow cooling in air results in almost complete reoxidation (δ=0). CaMnO_3−δ is an orthorhombic perovskite with a large range of nonstoichiometry (0⩽δ⩽0.30). The cubic to hexagonal phase transformation of the Sr-rich samples is accompanied by a large expansion of the lattice that is reduced by Ca substitution. The Ca/Sr-manganites are antiferromagnets with T_N of 170 K for x=0.5 and δ=0.02 and 120 K for x=1 and δ=0.05.     

Synthesis and properties of BaCe1−xYxO3−δ–BaWO4 composite protonic conductors

Barium cerate doped by trivalent rare earth metal ions is a potentially huge component of materials for electrochemical industry due to its high protonic conductivity. However, the poor chemical stability especially in the presence of CO₂, SO₂ or H₂O, resulting in decreasing the mechanical durability of obtained materials, limits their possible applications. The new approach towards stable ceramic protonic conductors with high electrical conductivity is presented. Thermal stability of yttrium doped (10 mol%) of BaCeO₃ was enhanced by forming the composite material BaCe_0.9Y_0.1O₃–BaWO₄ (10 mol% of BaWO₄). The synthesis was performed by solid-state reaction method. The detailed study of thermal decomposition of starting powders mixture was performed using thermogravimetry and differential thermal analysis (TG/DTA) techniques combined with Evolved Gas Analysis (EGA—mass spectrometry). Structure, phase composition and microstructure together with thermal stability of sintered materials were determined. The exposition tests were performed to characterise the stability of composites in carbon dioxide and water vapour-rich atmospheres. The samples were exposed to atmosphere containing CO₂/H₂O (7 % of CO₂ in air, 100 % RH) at temperature of 25 °C for 300 h. Thermal analysis supplied with mass spectrometry was applied to analyse the materials after the test. The results of this experiment showed better chemical resistance of composite material—BaCe_0.9Y_0.1O₃ with 10 mol% of BaWO₄ compared to single phase material.     

Untersuchungen in den Dreistoffen: Cr−W−Si und Mo−W−Si

Zusammenfassung Der Schnitt: Me₃Si (Me=Cr, W bzw. Mo, W) wird an Hand heißgepreßter und in Argon homogenisierter Legierungen untersucht; es läßt sich weder das metastabile W₃Si, noch eine W-reiche Mischphase von diesem Typ beobachten. Cr₃Si nimmt bei 1500°C etwa 20 Mol%, W₃Si auf, während Mo₃Si selbst bei 1900°C praktisch kein W₃Si löst (ev. wenige Mol%). Dagegen bestehen lückenlose Mischreihen zwischen den Me₅Si₃-Phasen mit W₅Si₃-Typ. Die grundsätzliche Aufteilung der Phasenfelder ist damit möglich.Mit 2 Abbildungen     

Nonstoichiometry and structural intergrowth in the CaFexMn1−xO3−y (0 ≤ x ≤ 1) system

An electron diffraction and microscopy study of the CaFe_xMn_1−xO_3−y system treated at 1100°C in air has been performed. An increase of y is accompanied by an increase of the cubic perovskite substructure parameter, the nonstoichiometry being accommodated in several ways. The system contains two solid solutions of the perovskite-type (P) and of the brownmillerite-type (B) and also an intermediate phase (x = 0.6) which makes disordered intergrowth with the B-type solid solution. These results are discussed in terms of multitwinning, randomly dispersed oxygen deficiency, and ordered and disordered intergrowth formation.     

Magnetische Messungen an den Teilsystemen TiC−ZrC,TiC−HfC,ZrC−HfC,TiC−VC,TiC−NbC,TiC−TaC und NbC−TaC

Ohne ZusammenfassungMit 3 Abbildungen     

An In-Situ Cyanidation Strategy To Access Tetracyanodiacenaphthoanthracene Diimides with High Electron Mobilities Exceeding 10 cm2 V−1 s−1

A family of novel highly π-extended tetracyano-substituted acene diimides, named as tetracyanodiacenaphthoanthracene diimides (TCDADIs), have been synthesized using a facile four-fold Knoevenagel condensation strategy. Unlike conventional cyano substitution reactions, our approach enables access to a large π-conjugated backbone with the in-situ formation of four cyano substitutents at room temperature while avoiding extra cyano-functionalization reactions. TCDADIs decorated with different N-alkyl substituents present good solubility, near-coplanar backbones, good crystallinity, and low-lying lowest unoccupied molecular orbital energies of −4.33 eV, all of which contribute to desirable electron-transport performance when applied in organic field-effect transistors (OFET). The highest electron mobility of an OFET based on a 2-hexyldecyl-substituted TCDADI single crystal reaches 12.6 cm² V⁻¹ s⁻¹, which is not only among the highest values for the reported n-type organic semiconductor materials (OSMs) but also exceeds that of most n-type OSMs decorated with imide units.     

Electrical and electro-chemical characterisation of La0.99Fe1−x Ni x O3−δ perovskites

(LFN, 0<x<0.6) perovskites were synthesised by a solid-state route and were characterised by powder XRD, dilatometry, four-point DC conductivity measurements and electro-chemical impedance spectroscopy (EIS) on cone-shaped electrodes using a Ce_1.9Gd_0.1O_1.95 (CGO10) electrolyte. All the compounds were of single phase, and they belong to either the cubic or the hexagonal crystal system. The thermal expansion coefficient (TEC) was in the range 10.7*10⁻⁶ K⁻¹ to 13.4*10⁻⁶ K⁻¹, which continued to increase with increasing nickel content. The highest electronic conductivity was measured for the composition giving a value of 670 S/cm at 380 °C. The highest electro-chemical performance was measured for the composition giving an area specific resistance as low as 5.5 Ωcm² at 600 °C based on EIS measurements on a cone-shaped electrode. Composite cathodes made from and CGO10 revealed a rather low performance due to an un-optimised micro-structure.

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Magnetische Kernresonanzuntersuchungen an Ti−C−H-Legierungen

Ohne ZusammenfassungMit 4 Abbildungen