Über die Verbindung Sr7Mn4O15 und Beziehungen zur Struktur von Sr2MnO4 und α-SrMnO3

On the Compound Sr₇Mn₄O₁₅ and Structure Relations to Sr₂MnO₄ and α-SrMnO₃ The “compound” hitherto described as a α modification of Sr₂MnO₄ is shown to consist of a mixture of SrO and the new monoclinic compound Sr₇Mn₄O₁₅ crystallizing in the space group P 2₁/c, a = 681.78(6), b = 962.24(8), c = 1038.0(1) pm, β = 91.886(7)°, Z = 2. Up to 0.3 mm long black crystals were grown from prereacted Sr₇Mn₄O₁₅, SrO, and SrCl₂ at 1350°C in a sealed platinum tube under argon. Its structure is related to α-SrMnO₃. It contains layers of cornershared double octahedra [O_2/2OMnO₃MnO₂O_1/2]^7? parallel to (100). Above 100 K the magnetism of Sr₇Mn₄O₁₅ follows the Curie Weiss law with Θ ～ -426 K and a moment μ_eff = 3.62 μ_B corresponding Mn⁴⁺.     

Über Glasbildung und Eigenschaften von Chalkogenidsystemen. IV. Bleithiogermanat (II,IV)-Gläser und ihre Eigenschaften

On Glass-Forming and Properties of Chalkogenide Systems. IV. Leadthiogermanate(II, IV) Glasses and their Properties PbS forms with GeS₂ in the presence of GeS stable glasses in a large range of composition. Melts containing an excess of sulphur yield inhomogenious products. Substituting PbS for GeS, the values of the atomic volume of the glasses at first decrease. The glass transition points as well as the optical and electrical properties are noticed and the crystalline phases received on annealing are discussed with respect to the glass-forming region. The results give the fundamentals to consider the vitreous materials of the system PbS? GeS? GeS₂ as leadthiogermanate(II, IV) glasses.     

Thermoanalytic characterization of NiMn2O4 formation

Comparative thermogravimetric and heat-flux DSC investigations of phase formations by heating of sinteractive powders, which were prepared by thermal decomposition of a NiCO₃ MnCO₃=12 mixture and thermal decomposition of oxalate mixed crystals NiMn₂(C₂O₄)₃.6H₂O, show the metastability of the defect spinel from the oxalate precursor and its high reactivity.Dilatometric shrinkage measurements show that reaction sintering leads to the shrinkage and maximum shrinkage rate at lower temperatures. Decomposition of the spinel NiMn₂O₄ under NiO separation and O₂ release at 975 in oxygen atmosphere is in contrast to the known phase diagram. Utilization of the thermodynamic driving force of the primarily formed metastable oxide phase and the NiMn₂O₄ formation leads, supported by a sinteradditive, to high density semiconductor ceramics.

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Zusammenfassung Vergleichende thermogravimetrische und WÄrmeflu\-DSC Untersuchungen der Phasenbildungsprozesse beim Aufheizen sinteraktiver Pulver, erhalten aus der thermischen Zersetzung von NiCO₃MnCO₃=12 Mischungen bzw. Zersetzung von Oxalatmischkristallen NiMn₂(C₂O₄)₃.6H₂O zeigen die MetastabilitÄt des Defektspinells aus der Oxalatvorstufe, sowie seine erhöhte ReaktivitÄt. Wie dilatometrische Schwindungsmessungen belegen, führt das reaktive Sintern zum Schwindungsbeginn und Maximum der Schwindungsgeschwindigkeit bei erniedrigter Temperatur. Die Zersetzung des Spinells NiMn₂O₄ unter NiO Ausscheidung und Sauerstoffabgabe ab 975C in SauerstoffatmosphÄre steht im Widerspruch zum bekannten Phasendiagramm. Bei Nutzung thermodynamischer TriebkrÄfte primÄr entstandener metastabiler Oxidphase und der NiMn₂O₄ Bildung werden, unterstützt durch den Zusatz von Sinterhilfsmittel, Halbleiterkeramiken hoher Dichte erhalten.

     

Festkörperaktivität und Mechanismen in Oxidsystemen. X. Untersuchung der Umsetzung von α-Fe2O3 mit BaCO3 mittels RBS-Spektrometrie

Solid State Reactivity and Mechanisms in Oxide Systems. X Investigation of the Reaction of α-Fe₂O₃ with BaCO₃ by RBS-Spectrometry Plate-like shaped α-Fe₂O₃ single crystals with the hexagonal axis perpendicular to the plane are characterized by Rutherford-Back-Scattering measurements. The preparation of dense BaCO₃ layers of a defined thickness is reported. The reaction at 650°C and 800°C leads to the formation of BaFe₂O₄ at the surface. Supported by model calculations the RBS spectra are interpreted by a sequence of phases which are in accordance with the phase diagram. PbO evaporates from the α-Fe₂O₃ single crystal surface at 500°C without reaction.     

Solid state reactivity and mechanisms in oxide systems

Starting from oxalate mixed crystals Ni_xMn_3?x(C₂O₄)₃·6H₂O thermal decomposition at reduced oxygen partial pressure (po₂= 2%) leads to the formation of NiMn₂O₄ (x = 1) at metastable conditions. Ni_1.5Mn_1.5O₄ (x = 1.5) existing in the metastable state only has been also prepared. The spinel compounds both are of the highly inversed type. Following a sol-gel preparation route Mg₂TiO₄ has been also found to be formed in the metastable state. Annealing results in decomposition of the compounds providing NiMnO₃ and 1/2α-Mn₂O₃ or NiMnO₃ only or MgTiO₃ and MgO, respectively. The reaction rates observed are lower for NiMn₂O₄ and Ni_1.5Mn_1.5O₄ than for Mg₂TiO₄ decomposition. The reverse reaction of NiMn₂O₄ formation above 730°C shows an endothermic enthalpy of +61 kJ·mol^?1. For Mg₂TiO₄ formation above 1050°C an endothermic enthalpy of +19.3 kJ·mol^?1 is found. The results are discussed in terms of structural features of the oxides.     

Über Strukturbeziehungen bei Erdalkalivanadin (IV,V)-oxiden

It is reported on compounds and their structural relations in the systems MeV^v-kO_3,5–k/2 with Me = Ca, Sr, Ba. The index k shows values from zero to one. According to the kind of Me-ions different phases are found. CaVO₃ und SrVO₃ crystallize in a perovskit-type. BaVO₃ crystallizes in a structure deriving from the Ba₃V₂O₈-type. X-ray analysis is confirmed by density- and NMR-measurements. Compounds of mixed oxidation numbers for Vanadium are only observed in the Ba and Sr-systems. Likewise their structures are derived from the Ba₃V₂O₈-type.     

Über Glasbildung und Eigenschaften von Chalkogenidsystemen (XII). Das Phasendiagramm SnS-GeS2

SnGeS₃ is the single ternary compound in the system SnS–GeS₂. The incongruent melting happens at 613°C. There is a eutectic mixture at the molar ration SnGeS₃: SnS = 1 which melts at 580°C. Samples of the eutectic composition form slightly undercooled melts which are related to the glass forming tendency found in the system SnS–GeS–GeS₂.     

Glass formation and properties of chalcogenide systems XVIII. On glass formation in the system GePbSeTe

The glass formation range of the system GePbSeTe has been investigated. For selected series properties such as the mole volume, glass transition temperature and the electrical direct current conductivity are discussed with respect to their dependence on composition. For some series the results can be compared with the properties of glasses containing Sn instead of Pb. The change in the energy gap for the crystalline compounds SnSe, SnTe, PbSe and PbTe is reflected by the data of the Sn or Pb containing glasses.