Spinelle mit substituierten Nichtmetallfeilgittern. II. Herstellung von Einkristallen im System CdCr2(S1−xSex)4

Single crystals of the system CdCr₂(S_1?xSe_x)₄ have been prepared by chemical transport with I₂/AlCl₃ mixtures and by flux growth from solutions in molten CdCl₂.     

Festkörperreaktionen in Chalkogenidsysfemen,IV [1]: Röntgenographische und elektrische Untersuchungen am System HgCr2(SexS1–x)4

Inhaltsübersicht. Im Spinellsystem HgCr₂Se_xS_1–x)₄ besteht im Gegensatz zu den entsprechenden Zink- und Cadmiumverbindungen, die lückenlose Mischkristallreihen bilden, zwischen 0,20 < x < 0.75 einp Mischungslücke. Im Bereich der Mischungslücke werden HgSe und Cr₂S_3–ySe_y-Mischkristalle gebildet. Die Gitterkonstanten der Spinellmischkristalle erfüllen nur auf der selenreichen Seite des Phasendiagramms die Végardsche Regel. Der Reaktionsverlauf wurde mit Hilfe von Leitfähigkeitsmessungen sowie thermoanalytischer Untersuchungen verfolgt. Über die Möglichkeit der Spinellbildung des Systems wird diskutiert. X-ray and Electric Measurements on the HgCr₂(Se_xS_1–x)₄ System Abstract. In the HgCr₂(Se_xS_1–x)₄ system there is no spinel structure in the 0.20 < x < 0.75 concentration range. In the miscibility gap the formation of HgSe and Cr₂8_3–ySe_y mixed crystals has been noticed. The lattice constants of the spinel solid solutions obey Végard's law only on the selenium-rich side of the phase diagram. Both the temperature dependence of electric conductivity and the thermal analysis of the starting mixtures were studied. The possibility of formation of spinels in the system is discussed.     

Spin glasses in CdCr2S4-ZnCr2S4 solid solutions

Magnetic properties of the continuous series of the solid solutions formed by the ferromagnet CdCr₂S₄ and antiferromagnet ZnCr₂S₄ compounds have been studied. The concentration and temperature boundaries of the magnetically active phases coexisting in the Cd_{1 ? x} Zn _x Cr₂S₄ system have been determined. It has been established that the ferromagnetic samples based on CdCr₂S₄ lie in the interval of concentrations 0 < x < 0.20, and the antiferromagnetic samples based on ZnCr₂S₄ are located in the interval of 0.9 < x < 1.0. The widest concentration interval (0.2 < x < 0.9) corresponds to spin glasses. The results obtained are discussed based on the percolation model.     

Mischkristallbildung in den Systemen Co1−x Ni x Cr2S4, Cu1−x Ni x Cr2S4 und Co1−x Cu x Cr2S4 Chromchalkogenide, 5. Mitt.

Zusammenfassung Durch Zusammensintern der Elemente bzw, der binären Sulfide wurde die gegenseitige Mischbarkeit in den Systemen CoCr₂S₄–NiCr₂S₄, CuCr₂S₄–NiCr₂S₄ und CoCr₂S₄–CuCr₂S₄ untersucht. In den Thiospinellen CoCr₂S₄ und CuCr₂S₄ können bis zu 20 (26) At% des Kobalts (Kupfers) durch Nickel substituiert werden (950°C), in das monokline NiCr₂S₄ wird nur wenig Kobalt bzw. Kupfer eingebaut. Zwischen dem halbleitenden, ferrimagnetischen Kobaltchromthiospinell und der metallisch leitenden, ferromagnetischen Kupferverbindung wurde lückenlose Mischkristallbildung beobachtet. Der von derVegardschen Regel abweichende Verlauf der Gitterkonstanten wird im Vergleich mit dem elektrischen und magnetischen Verhalten der Mischkristallreihe diskutiert.

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Chromium chalcogenides, V. Miscibility within the SystemsCoCr ₂S₄–NiCr₂S₄, CuCr₂S₄–NiCr₂S₄ andCoCr ₂S₄–CuCr₂S₄

The miscibility within the systems CoCr₂S₄–NiCr₂S₄, CuCr₂S₄–NiCr₂S₄ and CoCr₂S₄–CuCr₂S₄ was studied by annealing the elements or binary sulphides. In the thiospinels CoCr₂S₄ and CuCr₂S₄, 20 per cent of cobalt and 26 per cent of copper, resp., can be substituted by nickel at 950°C. In monoclinic NiCr₂S₄, only small amounts of cobalt or copper are dissolved. The formation of a complete solid solution series was observed between the semiconducting ferrimagnetic CoCr₂S₄ and the metallic conducting ferromagnetic CuCr₂S₄. The deviation fromVegard's rule of lattice constants is discussed with respect to the electrical and magnetic behaviour of the solid solution series.

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Mit 3 Abbildungen     

Festköperreaktionen in Chalkogenidsystemen. III. Bestimmung der Aktivierungsenergie von Pulvereaktionen aus Leitfähigkeitsglowkurven

In the case of the formation of thiospinels (MnCr₂S₄, ZnCr₂S₄ and CdCr₂S₄) a simple method for the determination of the activation energy of solid state reactions in polycrystalline samples by means of conductivity measurements is shown. The maxima and minima of conductivity (glow curve maxima and -minima) in the σ vs T-curves got by annealing with linearly increasing temperature are shifted towards higher temperatures with increasing rate of heating(q). By plotting ln (q/T) vs 1/T_σmax a straight line results. The activation energy of the reaction may be deduced from the slope of this straight line in analogy to the determination of the trap depth of electrons from glow curves observed in thermoluminescence.     

Der Einfluß von Sauerstoff,Wasser, Chlor und Brom auf den Transport von Kohlenstoff in fluorhaltigen Systemen

Quaternary System ZnSe - Cr₂Se₃ - In₂Se₃ The section Zn_1-xIn_0.667xCr₂Se₄ and ZnCr_2-yIn_ySe₄ as well as some samples of compositions outside these joins of the quaternary system ZnSe Cr₂Se₃ - In₂Se₃ were studied with the help of X-ray Guinier photographs of quenched samples. Whereas no detectable amounts of chromium can be incorporated into ZnIn₂Se₄ of the thiogallate structure (MnIn₂Te₄ type) in the case of the spinel ZnCr₂Se₄ (a = 1050.0 pm) up to 21 mol % of chromium and up to 20 mol % of zinc can be substituted by indium. However, spinel type solid solutions with larger indium content (up to a = 1076 pm) are formed by coincident substitution of both zinc and chromium corresponding to Zn_1-xIn_0.667xCr_2-yIn_ySe₄ (0 < x + y < 0.6) with indium in both tetrahedral and octahedral lattice sites.     

Phase relationships of the quaternary systems MCr2Se4MGa2Se4 (M = Mn,Fe, Co,Ni): New layered ZnIn2S4-III type selenides

The phase relationships of the quaternary systems MCr₂Se₄MGa₂Se₄ (M = Mn, Fe, Co, Ni) and MV₂S₄MGa₂S₄ (M = Fe, Ni) and the ternary system NiSGa₂S₃ were studied by X-ray phase analyses with the aim to prepare new layered structure and spinel-type chalcides. The hitherto unknown selenides MnCr_0.5Ga_1.5Se₄, FeCr_0.5Ga_1.5Se₄, CoCr_0.5Ga_1.5Se₄, and (Ni, Cr, Ga, □)₃Se₄ (all ZnIn₂S₄-III type) were obtained and characterized by X-ray and FIR studies. No quaternary chalcides are formed in the systems MV₂S₄MGa₂S₄; ternary NiGa₂Se₄ and CoGa₂Se₄ were likewise not obtained. Whereas the phase widths of the end-member phases are small (with the exception of α′-Ga₂S₃ at 1000°C) because of the strong tetrahedral and octahedral site preferences of gallium and both chromium and vanadium, respectively, the quaternary selenides form solid solutions of the type MCr_2−2xGa_2xSe₄ with x = 0.65-0.80 for M = Mn and Fe.     

Conductibilité electrique aux basses températures des composés binaires Cr2X3 et Cr3X4 (X = S,Se ou Te)

Electrical resistivity of some binary compounds Cr₂X₃ and Cr₃X₄ (X = S, Se or Te) is studied on polycrystalline samples with the four point probe method, at temperatures between 4.2 and about 330 K. A metallic behavior is observed on Cr₂Te₃, Cr₃Te₄, Cr₃S₄ and the 3c′ form of Cr₂Se₃. Some other compounds are semiconductors: Cr₃Se₄ (E_300K ≈ 0.07 eV; E_4.2K = 2.07 × 10^?4 eV), the 2c′ form of Cr_2+εSe₃ (E_300K ≈ 0.074 eV; E_4.2K = 2.76 × 10^?4 eV) and the 3c′ form of Cr₂S₃ (E_275K ≈ 0.55 eV). The observed results seem to be closely related to the nature of the octahedral neighborhood of the cations.     

Phase relationships in the systems MSCr2S3In2S3 (M = Co,Cd, Hg)

The phase diagrams of the quaternary systems MSCr₂S₃In₂S₃, with M = Co, Cd, and Hg, were studied with the help of X-ray powder photographs of quenched samples, high-temperature X-ray diffraction patterns, DTA and TG measurements, and far-infrared spectra. Because indium sulfides do react with silica tubes, alumina crucibles must be used for annealing the samples. Complete series of mixed crystals are formed among the spinel-type compounds MCr₂S₄, MIn₂S₄ (M = Cd, Hg), and In₂S₃. HgIn₂S₄ is decomposed at temperatures above 300°C. In the sections CoCr₂S₄CoIn₂S₄ and CoCr₂S₄In₂S₃ relatively large miscibility gaps exist due to the change from normal to inverse spinel structure. But the interchangeability of both systems increases with increasing temperature, and at temperatures above 1000°C, complete series of solid solutions are formed, which can be quenched to ambient temperature. Superstructure ordering like that of ordered α-In₂S₃ has been found in the In-rich region of the MIn₂S₄In₂S₃ solid solutions. The unit cell dimensions of all stoichiometric and phase boundary compounds, e.g., Cd_1.15In_1.9S₄, including the chromium spinels MCr₂S₄ (M = Mn, Zn) and ZnCr₂Se₄, are given and discussed in terms of possible deviations from stoichiometry.     

Characterization of TlCu7S4, a crookesite analogue

Previous claims of a compound TlCu₉S₅ are rejected. The true composition is TlCu₇S₄, the compound being isostructural with NH₄Cu₇S₄ and TlCu₇Se₄ (crookesite). The body-centred tetragonal cell (a=10.1797 Å andc=3.8585 Å) contains two formula units.

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Beschreibung von TlCu₇S₄, einer dem Crookesit analogen Verbindung (Kurze Mitteilung)

Zusammenfassung Frühere Feststellungen, daß im pseudobinären System Tl₂S-Cu₂S eine Verbindung TlCu₉S₅ existiert, erwiesen sich als unzutreffend. Die korrekte Formel muß TlCu₇S₄ lauten. TlCu₇S₄ besitzt eine raumzentrierte tetragonale Elementarzelle (a=10.1797 Å,c=3.8585 Å;Z=2) und ist isostrukturell mit NH₄Cu₇S₄ und TlCu₇Se₄ (Crookesit).

     

Structural and magnetic properties of Zn1−xSbxCr2−x/3Se4 (x=0.11, 0.16 and 0.20) single crystals

Single crystals of Zn_1−xSb_xCr_2−x/3Se₄ based on the ZnCr₂Se₄ spinel, which is known to exhibit interesting magnetic and electronic transport properties, have been prepared by solid state reaction from the appropriate selenides. Three compounds of different Sb content (x=0.11, 0.16, and 0.20) were studied by X-ray diffraction, X-ray photoelectron scattering technique and macroscopic magnetic measurements with the aim to determine (i) stability of the cubic symmetry and (ii) influence of the Sb admixture on the magnetic properties. The results show that the Sb³⁺ and Zn²⁺ ions share the tetrahedral sites in the spinel structure, while the Cr³⁺ions carrying magnetic moments, are located in the octahedral sites. The X-ray photoelectron spectroscopy (XPS) data indicate that in this series of compounds the chromium ions have a 3d³ electronic configuration. The three samples studied order antiferromagnetically at low temperatures, with the magnetic characteristics being hardly altered with respect to those reported for the parent ZnCr₂Se₄ compound.     

IR-Spektroskopische und Röntgenographische Untersuchungen an Thiospinellmischkristallen

The effect of the tetrahedral and octahedral coordinated metal and nonmetal atoms on the vibrational spectra of spinels is studied by investigation of mixed crystals and defect spinels like In₂S₃. The following solid solutions of chromium thiospinels and indium sulfides have been prepared and investigated by X-rays and FIR-spectroscopy: Hg_xZn_{1 ? x}Cr₂S₄ (I), ZnIn_xCr_{2 ? x}S₄ (II), CdIn_xCr_{2 ? x}S₄ (III), ZnCr₂Se_xS_{4 ? x} (IV), α-In₂S₃ (V), β-In₂S₃ (VI) and Cr_xIn_{2 ? x}S₃ (VII). The lattice constants of (I), (III), (IV) and (VII) obey Vegard's rule. (III) has a miscibility gap between x = 0.3 and x = 1.8. The spectroscopic behavior of the solid solutions (all the four peaks of the spinel spectra split or shift) can not be interpreted on the basis of internal vibrations of different coordination polyhedra. An explanation of the additional peaks in the spectra of the mixed crystals is given according to order of the atoms or distortion of the spinel structure.     

Röntgenographische und schwingungsspektroskopische Untersuchungen an Spinell-Mischkristallen des Systems (Zn,Ga) Cr2Se4

X-ray and I. R. Spectroscopic Studies on Spinel Solid Solutions of the Zn_1–xGa_0.67xCr₂Se₄ System With the aim to get new compounds with spinel defect structure of the ß-In₂S₃ type, we studied the phase diagram of the Zn_1–xGa_0.67xCr₂Se₄ system. The spinel type solid solutions formed within x = 0—0.6 show a relatively large phase width with respect to the metal selenium ratio, i. e. the parameter z in the formula Zn_1–xGa_0.67(x+0.5z)Cr_2–z^IIICr_z^IISe₄. Ternary Ga_0.67Cr₂Se₄ does not exist, it decomposes to Cr₂Se₃ and Ga₂Se₃. Instead of the ß-In₂S₃ type, superstructure reflections of LiFeCr₄O₈ type are observed.     

Neue Verbindungen mit KCu4S3-Struktur

TlCu₄S₃, TlCu₄Se₃, KCu₄Se₃, RbCu₄Se₃, CsCu₄S₃ and CsCu₄Se₃ were prepared by direct synthesis or by the carbonate melt method. They are isotypic with KCu₄S₃, space group P4/mmm,Z=1. The lattice parameters are: TlCu₄S₃:a=3.894(1)Å,c=9.33(1)Å, TlCu₄Se₃:a=3.974(4)Å,c=9.84(2)Å, KCu₄Se₃:a=3.963(4)Å,c=9.81(3)Å, RbCu₄Se₃:a=4.048(2)Å,c=9.86(1)Å, CsCu₄S₃:a=3.964(3)Å,c=9.67(1)Å,and CsCu₄Se₃:a=4.091(2)Å,c=10.08(1)Å. The crystal structure of TlCu₄S₃ was refined from single crystal diffractometer data. Isotypy of the other compounds was checked by visual inspection of rotating crystal orDebye Scherrer film intensities. The relationship between the crystal structures of the MCu₄ X ₃-phases, the TlT₂ X ₂-phases (ThCr₂Si₂ type) and the anti-CaF₂ type is shown.

Hern Professor Dr.H. Bittner zum 60. Geburtstag in Verehrung gewidmet.     

Neue Alkalimetallchromchalkogenide und ihre Struktursystematik

New Alkali Metal Chromium Chalcogenides and their Structural Classification The compounds RbCr₃S₅, K₃Cr₁₁S₁₈, RbCr₅Se₈ and CsCr₅Se₈ could be obtained in the form of wellshaped crystals via fusion reactions of the alkali metal carbonates with chromium and the corresponding chalcogen. The compounds crystallize in the monoclinic space groups C2/m (RbCr₃S₅: a = 19.372(3) Å, b = 3.498(1) Å, c = 12.119(2) Å, β = 122.78(1)°, Z = 4; K₃Cr₁₁S₁₈: a = 41.876(3) Å, b = 3.463(1) Å, c = 16.315(3) Å, β = 150.07(1)°, Z = 2; RbCr₅Se₈: a = 18.737(2) Å, b = 3.623(1) Å; c = 9.016(1) Å, β = 104.65(1)°, Z = 2; CsCr₅Se₈: a = 18.795(2) Å, b = 3.637(1) Å, c = 9.104(1) Å, β = 104.52(1)°, Z = 2). We propose a structure classification from group-subgroup-relations. MAPLE calculations reveal that the reactions of the binary chalcogenides to yield the ternary compounds are exothermic in each case and are dependent on the chromium/alkali metal ratio in the ternary chalcogenides.     

Formation of the Ni–CrOx/MgO and Ni/MgO Catalysts for Carbon Dioxide Reforming of Methane

Temperature-programmed reduction by hydrogen, temperature-programmed desorption of O₂, local X-ray spectral analysis, and scanning electron microscopy are used to study redox processes occurring on the Ni–Cr₂O₃/MgO and Ni/MgO catalysts for carbon dioxide reforming of methane. The reduction of Ni/MgO leads to the formation of nickel clusters distributed over the surface of MgO. During the reduction of NiO–Cr₂O₃/MgO, chromates are transformed into chromites, and then nickel is formed by the reduction of spinel NiCr₂O₄. Reoxidation leads to the oxidized structures NiO, NiCr₂O₄, and NiCrO₄.     

Gitterschwingungsspektren XVIII.1 Chromthio- und Chromselenospinelle mit 1:1-Ordnung auf den Tetraederpl?tzen

The infrared spectra of spinel-type compounds A⁺A³⁺ Cr₄X₈ (A⁺ = Li, Cu, Ag; A³⁺ = Al, Ga, In; X = S, Se) have been measured. The spectra show that the spinels LiGaCr₄S₈, LiInCr₄S₈, CuGaCr₄S₈, CuInCr₄S₈, AgInCr₄S₈, CuGaCr₄Se₈, CuInCr₄Se₈, and AgInCr₄Se₈, whose structures cannot be determined by X-ray methods in all cases, have a structure with 1:1 ordering on the tetrahedral site (space group $\text{F}\text{4}\text{3m}$). No ordering takes place in AgGaCr₄S₈. The spectra of the ordered spinels are discussed in relation to two-mode type spectra of spinel mixed crystals.     

The effects of doping ferromagnetic spinel CdCr2Se4 with Sb ions

Semiconducting spinel CdCr₂Se₄ orders ferromagnetically below T_C=130 K. A series of single-crystals of CdCr₂Se₄ doped with Sb³⁺ ions has been synthesized in order to study an effect of the substitution on the cation distribution and the magnetic properties. The compounds of Cd_ySb_xCr_zSe₄ have been investigated by means of X-ray diffraction, magnetization measurements and electron spin resonance spectroscopy. Two selected samples of the composition (Cd_1−xSb_x)[Cr₂]Se₄ with x=0.13 and 0.44 retained cubic symmetry with space group . The unit cell parameter appeared to be sensitive to the concentration of Sb³⁺ admixture: it increases with x, despite a close similarity in the ionic radii of Cd²⁺ and Sb³⁺ in tetrahedral coordination. Upon partial substitution of Cd²⁺ by Sb³ no obvious change in the Curie temperature was observed, however, the effective magnetic moment slightly increased, what may result from the appearance of Cr²⁺ ions. The characteristic feature of the system studied is an extended range of short-range magnetic order, in which the magnetic properties in the paramagnetic state are governed by the formation of ferromagnetic clusters, as indicated by both the bulk magnetometric and spectroscopic data.     

Konzentrationen von Isomeren des Typs P m As4−m X 3 in P4S3-As4S3- und P4Se3-As4Se3-Mischungen

The reactions of P₄S₃ with As₄S₃ and of P₄Se₃ with As₄Se₃ in the molten state yields molecules of the type P _m As_4–m S₃ and P _m As_4–m Se₃, respectively. A method was developed to separate the different components by the HPLC technique, and to determine their concentrations. The identification of the isomers in the HPLC pattern was achieved with the aid of the LC-MS method. In the selenium system, the distribution of the different species is statistical. In the system P₄S₃-As₄S₃, the formation of PAs₃S₃ with one phosphorus atom in the apical position is favoured.

     

Etude structurale de combinaisons sulfurées et séleniées du molybdène. III. Structure cristalline de NiMo3S4

The crystals of NiMo₃S₄, are rhombohedral, space group $\text{R}\text{3}$, with two formula units in a cell: a = 6.462 Å, α = 94.68°.The structure was solved by the heavy atom method and refined by a full-matrix least-squares program to R = 0.077 for 1026 independent reflexions. The arrangement of Mo and S atoms in the cell is approximately the same as described before for Mo and Se atoms in Mo₃Se₄ and Ni_0.33Mo₃Se₄; the Ni atoms are situated along the channel based on x = 0, y = 0. However, in these two compounds the lattice of Se presents a covalent character when the lattice of S in NiMo₃S₄ has an essentially ionic character.