[en] The compounds Rh₂U₆S₁₅, Cs₂Ti₂U₆Se₁₅, Cs₂Cr₂U₆Se₁₅, and Cs₂Ti₂U₆Te₁₅ have been synthesized at 1173 K. All crystallize in space group O⁹_h - Im3-bar -m of the cubic system. Rh₂U₆S₁₅ has a framework structure with three-dimensional channels. The compounds Cs₂Ti₂U₆Se₁₅, Cs₂Cr₂U₆Se₁₅, and Cs₂Ti₂U₆Te₁₅ have structures similar to that of Rh₂U₆S₁₅, but with Cs cations variably filling the channels. In all four structures the transition element is octahedrally coordinated by chalcogens and the uranium atom is in a bi-capped trigonal-prismatic arrangement. The temperature dependence of the magnetic susceptibility of Cs₂Cr₂U₆Se₁₅ implies both Cr and U magnetic contributions. From these data the compound is not antiferromagnetic, but it could have either a ferrimagnetic or a ferromagnetic ground state. (authors)

[en] A new quaternary uranium(V) selenide, Ba₈PdU₂Se₁₂(Se₂)₂, has been synthesized by reaction of elements at 1173 K. A single-crystal X-ray diffraction study shows that the compound crystallizes in a new structure type with two formula units in space group D_2h¹²-Pnnm of the orthorhombic crystal system with cell constants of a=9.490(1), b=12.240(2),and c=13.780(3) Angstroms. Its crystal structure consists of [PdU₂Se₁₂^12-] units where U atoms are coordinated to six Se atoms in octahedral geometry and Pd atoms are coordinated to four Se atoms in square-planar geometry.These [PdU₂Se₁₂^12-] units are separated by Ba to result in a salt-like crystal structure. This compound also contains Se₂^2- dimers that are part of Ba coordination polyhedra. The formula charge balances as (Ba²⁺)₈(Pd²⁺)(U⁵⁺)₂(Se^2-)₁₂(Se₂^2-)₂. Theoretical calculations predict antiferromagnetic semiconducting behavior for this compound with a band gap of 1.6 eV. Temperature-dependent four-probe resistivity measurements on single crystal confirm the semiconducting nature with an activation energy of 0.18(1)eV. (authors)

[en] The rare earth oxysulfate series Ln²O²SO⁴ (Ln = La, Gd, Y) was synthesized by two different thermal decomposition methods. The complex ion (LnO)/sub n//sup n+/) existing in the structure of various oxysalts seems to have a major effect on the appearance of the spectra. Then it is possible to derive sets of crystal field parameters simulating the spectra, by using the C/sub 4v/ → C/sub 2v/ descending symmetry procedure. Moreover, an alternative method for determining these parameters is described when a C/sub 2v/ point site symmetry is distorted from D/sub 3h/

[en] Two new ternary lanthanide (Ln) uranium selenides, Er₃USe₈ and Yb₃USe₈, were synthesized at 1198 K using NaI as a flux. Single-crystal X-ray studies show these two compounds to be isostructural and to crystallize in space group D2h 11-Pbcm of the orthorhombic crystal system. The Ln and U atoms are disordered on the same crystallographic site in these crystal structures. Each Ln/U atom is coordinated to eight Se atoms in a bi-capped trigonal prism, and sharing of these (Ln/U)Se₈ units creates a three-dimensional network. Se2 atoms are connected to each other to form infinite one-dimensional chains along the c axis. In these chains, the two Se atoms are separated by about 2.74 Angstroms, a distance intermediate to those of a Se-Se single bond and a van der Waals interaction. Temperature-dependent resistivity measurements show that Er₃USe₈ and Yb₃USe₈ are semiconductors with activation energies of 0.08 (1) and 0.17(1)eV, respectively. (authors)

[en] The isothermal decomposition of any ternary oxide A/sub x/B/sub y/O/sub z/ on liberation of n moles of oxygen at a constant pressure is found to be driven by the mixing entropy ΔS/sub m/ = -nRlnP/sub O₂/ of the total entropy change ΔS = ΔS⁰ + ΔS/sub m/. The stability of A/sub x/B/sub y/O/sub z/ towards isothermal decomposition into a biphasic solid mixture is derived from the equilibrium condition ΔG* = 0 as functions of standard changes ΔH⁰ and ΔS⁰. Assuming ΔS⁰ = 44n and calculating ΔH⁰ in terms of lattice energies U(ABO₃) and U(A₂O₃), the stability of perovskites St(ABO₃) = -logP*/sub O₂/(A = La, Sm, Dy; B = Mn, Fe) is given as a function of the ionic radius of the A³⁺ ion. The calculated stability agrees well with that observed. The effect of electronic entropy change ΔS/sub e/ on ΔS⁰ is demonstrated for AFeO₃

[en] The heat of reaction and equilibrium pressure for the oxidation reaction TbO/sub 1.5 + x/ + (3/28 - x/2)O₂ → (1/7)Tb₇O₁₂ have been measured by means of a Tian-Calvet-type calorimeter and a thermal balance. The results of the weight measurement show a reproducible hysteresis loop. The heat of reaction has been measured along the oxidation branch of the hysteresis loop. The partial molar enthalpy indicates four distinct compositional regions. First, the TbO/sub 1.5 + x/ region which can be described in terms of a point defect model and strong interaction between neighboring excess oxygen atoms. Second, the region between TbO₁₅₄ and TbO₁₆₁ is interpreted as the intrinsic hysteresis region and discussed in terms of the regular solution model. Third, the region between TbO₁₆₁ and TbO₁₇₀ is recognized as a pseudophase region. Fourth, a region of eta phase exists in which the partial thermodynamic quantities can be compared with those of CeO₁₇₁₄, PrO₁₇₁₄, and TbO₁₇₁₄. The partial molar enthalpy was also measured for a scanning loop which is also interpreted in terms of the four regimes

[en] The phase relations in the Yb₂O₃-Fe₂O₃-CoO system at 1350 and 1300⁰C, the Yb₂O₃-Fe₂O₃-NiO system at 1300 and 1200⁰C, the Yb₂O₃-Fe₂O₃-CuO system at 1000⁰C, and the Yb₂O₃-Fe₂O₃-ZnO system at 1300⁰C were determined in air by means of a classical quenching method. New layered-type compounds, YbFeCoO₄ (a = 3.4295(5) angstrom, c = 25.198(3) angstrom), YbFeCuO₄ (a = 3.4808(2) angstrom, c = 24.100(2) angstrom), and YbFeZnO₄ (a = 3.4251(2) angstrom), c = 25.282(2) angstrom), which are isomorphous with YbFe₂O₄ (space group: R3m; a = 3.455(1) angstrom, c = 25.109(2) angstrom), and a new compound, Yb₂Cu₂O₅, were obtained. In the Yb₂O₃-Fe₂O₃-NiO system, there are no quaternary compounds

[en] The selenide systems of niobium and tantalum were investigated under high pressures in the composition limits of MX₂ to MX₃. Two distinct phases, NbSe₂ and NbSe₃, were obtained in the niobium system. In the tantalum system, there were three phases, TaSe₂, ''TaSe₃,'' which has been thought of as a triselenide, and stoichiometric TaSe₃. The ratio of Se/Ta in ''TaSe₃'' was 2.8. Conversions of the triselenides under high pressure to NbSe₂ or TaSe₂ were observed at the starting composition of Se/M = 2.0 and to ''TaSe₃'' at Se/Ta = 2.8

[en] La³WO⁶GAMMAl³ is representative of a group of rare earth chlorotungstates, where Ln can also be Ce, Pr, Nd, Sm, Eu, and Gd. The structure was determined and refined to an R value of 3.5%. The space group is P6³/m with La in 10-coordination and W in an unusual trigonally prismatic 6-coordination. The local site symmetry for W is D/sub 3h./ Powder diffraction data are reported for La³WO⁶Cl³. Diffuse reflectance, ir, Raman, and luminescence spectra are reported for pure La³WO⁶Cl³, as well as for the activators Sm, Eu, Tb, Dy, and Tm incorporated into this host

[en] Two samples containing 2-line ferrihydrite and copper oxide were synthesized by coprecipitation method, via variation of Fe3+ and Cu2+ precursors milimolar ratio (3:1 and 3:3.1), while the other synthesis parameters were kept constant. Annealing treatment at 1100 °C resulted in the formation of c-CuFe2O4-CuO-α-Fe2O3 and c-CuFe2O4-CuO nanocomposites, respectively. A comparison of properties of the prepared samples was performed by XRD, FTIR and EPR measurements. Formation mechanism of the nanocomposites is discussed with a reference to the influence of Jahn-Teller effect in CuO phase on the final CuFe2O4 structure. For the first time, it is shown that the amount of Fe3+ precursor is of key importance for the size of CuFe2O4 nanoparticles, and enables preparation of c-CuFe2O4 nanoparticles of the same crystallite size (46 nm) in different nanocomposite materials. © 2019 Elsevier Inc.