The preparation of Ln2MX5 where Ln = rare earths,M = Zr and Hf,and X = S,Se

Compounds of the title formula were prepared by reactions of the elements in evacuated silica tubes in the presence of iodine. The compounds formed for the following combinations: When M = Zr or Hf and X = S, all rare earths except Eu and Yb. When M = Zr and X = Se, rare earths between La and Tb, except Eu. When M = Hf and X = Se, rare earths La and Ce. X-Ray powder patterns were indexed on the basis of orthorhombic cells analogous to that of U₃S₅. Electrical measurements show high-resistivity semiconduction for La₂ZrS₅ and Ce₂HfS₅ but lower resistivity for Sm₂HfS₅, perhaps indicative of the presence of some Sm⁺².     

Conductivite ionique des oxydes Li8MO6 (M = Ce,Hf)

The electrical conductivity of the oxides Li₈CeO₆ and Li₈HfO₆, which are thermodynamically stable against Li (1), has been studied under oxygen atmosphere in the temperature range between room temperature and 200°C. As for Li₈ZrO₆ and Li₈SnO₆ (2), the materials can be considered as solid electrolytes with medium conductivity. The interpretation of the results, considering the Ca²⁺ ions as impurities, are in agreement with those based on the diffusion mechanisms of the Li⁺ ions recently established by ⁷Li NMR in isostructural oxides by Simpson et al. (3).     

Crystal structure and superconductivity of new ternary MTGe germanides (M = Ti,Zr,Hf and T = Ru,Os,Rh,Ir)

ZrIrGe and HfIrGe crystallize in the TiNiSi-type structure and exhibit a superconducting transition at 2.75K and 4.98K respectively. TiIrGe and HfRhGe have two allotropic varieties and their superconducting properties are strongly influenced by their crystal structure. On the other hand no superconducting transition has been observed above 1.6K for TiTGe (T = Ru,Os,Rh), ZrTGe (T = Ru,Os) and HfTGe (T = Ru,Os) which adopt either the ordered Fe₂P-type or the TiFeSi-type superstructure. This investigation shows clearly that the TiNiSi-type structure favors occurence of superconductivity in ternary germanides as previously found for ternary silicides.     

Medium-entropy(Me,Ti)0.1(Zr,Hf,Ce)0.9O2(Me = Y and Ta): Promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking

With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC) materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature ...     

New superconducting lead cuprate with 1201 structure, (Pb0.5B0.5) (SrLa)CuOz

New Pb-based superconducting cuprate with the 1201 structure has been synthesized in the (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z system. From X-ray powder diffraction study, the almost-single 1201 phase sample is found to be obtained at x = 1.0 and y = 0.5 for the nominal composition of (Pb_1 − yB_y)(Sr_2 − xLa_x)CuO_z. The crystal structure has a tetragonal symmetry with the lattice parameters of a = 0.3779 nm and c = 0.8654 nm. The sample shows an onset of superconductivity at about 32 K as measured by the temperature dependence of the DC magnetic susceptibility.     

A new family of superconducting silicides: The ThMxSi2−x compounds (M = Rh or Ir with 0 < x < 1) of α-ThSi2-type structure

New superconducting materials have been prepared by substitution of silicon by Rh or Ir atoms in the α-ThSi₂ disilicide. The ThM_xSi_2?x compounds crystallize in the tetragonal α-ThSi₂-type structure with a large homogeneity range: 0? x ? 0.96 for Rh and 0? x ? 1 for Ir. A sharp increase of the superconducting transition temperature T_cr is observed for x > 0.75 in both cases. Among the superconducting compounds with an α-ThSi₂-type structure, ThRh_0.96Si_1.04 and ThIrSi have the highest T_cr values with respectively 6.45 and 6.5 K about twice that of α-ThSi₂ (T_cr = 3.16 K). Superconductivity enhancement has been attributed to the formation of Rh-Rh or Ir-Ir metallic type bonding.     

Effect of Al2O3 concentration on zirconolite (Ca(Zr,Hf)Ti2O7) crystallization in (TiO2,ZrO2,HfO2)-rich SiO2–Al2O3–CaO–Na2O glasses

Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti₂O₇) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO₂–Al₂O₃–CaO–Na₂O–TiO₂–ZrO₂–HfO₂ system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al₂O₃ concentration in glass composition had a strong effect on the nucleation rate I _z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite + anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al³⁺ and (Ti⁴⁺, Zr⁴⁺, Hf⁴⁺) ions for their association with charge compensators cations to facilitate their incorporation in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predominantly in 4-fold coordination. Neodymium optical absorption and fluorescence spectroscopies showed that the Al₂O₃ concentration changes performed in this study had not significant effect on Nd³⁺ ions environment in glasses.     

Des conducteurs ioniques pseudo-bidimensionnels: Li8MO6 (M = Zr,Sn), Li7LO6 (L = Nb,Ta) et Li6In2O6

The ionic conductivity of the pseudo-2D oxides Li₈MO₆ (M = Zr, Sn), Li₇LO₆ (L = Nb, Ta) and Li₆In₂O₆ has been measured and related to their structures. The ideal lattice consists of octahedral sheets [(Li₂M)O₆]_n, [(Li□L)O₆]_n or [(In₂□)O₆]_n of CdI₂-type, between which 6 Li⁺ ions are inserted with a tetrahedral environment. As expected from the structures the highest lithium mobility is observed for Li₇LO₆ phases and the smallest one for Li₈MO₆.     

New ternary molybdenum chalcogenides containing Mo6 and Mo9 clusters: M2Mo15Se19 (M = K,Ba, In,Tl) and K2Mo15S19

New superconducting Mo^II compounds M₂Mo₁₅X₁₉ (M = K, Ba, In, Tl and X = Se; M = K and X = S have been found. These materials crystallize in a new structural type containing isolated Mo₆X₈ and Mo₉X₁₁ units. They are superconducting (T_c = 3.32 K for K₂Mo₁₅S₁₉), and have high initial slopes $\text{dHc}{}_2\text{dT}$ of the upper critical field.     

Crystal growth and luminescence of Sb3+-Doped Cs2NaMCl6 (M = Sc,Y, La)

Crystal growth and the luminescence properties of Cs₂NaMCl₆-Sb³⁺ (M = Sc, Y, La) are described. The emission consists of one band which shifts to lower energies for an increasing ionic radius of M³⁺ (i.e. from Sc via Y to La). The excitation bands of the luminescence of all three compounds are at the same energy and show a structure which can be explained by assuming a dynamical Jahn-Teller effect to be operative in the excited state of the Sb³⁺-ion.     

Synthesis, structure and dielectric characterization of Ln2Ti2−2xM2xO7(Ln=Gd, Er; M=Zr, Sn, Si)

The progress in wireless communications and information access has demanded the use of electronic ceramics exhibiting desired properties. To further our understanding of these properties, compounds in the Ln₂Ti_2-2xM_2xO₇ (Ln=Gd, Er; M=Zr, Sn, Si) systems were synthesized by ceramic methods and characterized by powder X-ray diffraction. The ZrO₂-doped Gd₂Ti_2−2xZr_2xO₇ compounds adopt the pyrochlore structure type and form a complete solid solution. Er₂Ti_2−2xZr_2xO₇ forms a pyrochlore solid solution for x<0.1. However, stoichiometric Er₂Zr₂O₇ does not form; instead Er₄Zr₃O₁₂ forms a with defect fluorite structure. The Sn-doped Ln₂Ti_2−2xSn_2xO₇ (Ln=Gd, Er) compounds form complete solid solutions, and the Si compounds adopt the pyrochlore structure up to x=0.05. At ambient temperature, dielectric constants range from 10 to 61 for Er₂Ti_2−2xZr_2xO₇ and 16-31 for Gd₂Ti_2−2xZr_2xO₇ with low dielectric loss (1×10⁻³) at 1 GHz.     

The preparation of some ternary sulphides MR2S4 (M = Ca,Cd; R = La,Sm,Er) and the melt growth of CaLa2S4

The Preparation of the binary sulphides CaS, La₂S₃, Er₂S₃, and Sm₂S₃ in high purity powder form from the elements is described, with the subsequent synthesis of ternary sulphides with Th₃P₄ and spinel structures. Single crystals of CaLa₂S₄ and CaLa₂S₄La₂S₃ solid solutions, up to 10 mm³ volume, have been grown from the melt in sealed crucibles using the Stöber technique.     

Phase relationships of the ternary chromium sulfides CrII1−xMxCrIII2S4 (M = Mn,Fe, Co) with Cr3S4 and spinel structure

The phase diagrams of the chromium sulfide systems Cr_1?xM_xCr₂S₄, Cr_1?xFe_xCr₂S₄, andCr_1?xCo_xCr₂S₄ were studied with the help of X-ray powder Guinier photographs of quenched samples. The phase widths of the monoclinic Fe₃Se₄ (Cr₃S₄) type solid solutions increase with increasing temperature from x < 0.1 below 500°C to x = 0.23, 0.45, and 0.44 for M = Mn, Fe, and Co, respectively, at 900°C. The observed alterations of the unit cell parameters, e.g. increase of the volume V, but decrease of the lattice constant a with increasing × for M = Mn and Fe, are discussed in terms of the ionic radii and metal-semiconductor transitions. The phase widths of the spinel type chromium sulfides MCr₂S₄ are very small for all temperatures studied. The relative stability of the Cr₃S₄ and the spinel structure can be interpreted using site preference and covalent bonding arguments.     

Citrate gel synthesis and characterization of (ZrO2)0.85(REO1.5)0.15 (RE = Y, Sc) solid solutions

By the citrate gel method, (ZrO₂)_0.85(REO_1.5)_0.15 (RE = Y, Sc) solid solutions in pure cubic fluorite structure were prepared at relatively low calcination temperatures. The existence of the strong coordination interaction between the COO⁻ groups of the ligands and metal ions could effectively prevent the segregation of metal ions during the gel formation. Upon heat treatment within 110-500 °C, the gel decomposed by multi-steps, with the formation of well-defined intermediate decomposition products, while, the bonding nature between COO⁻ groups and metal ions changed with temperature: unidentate (110-250 °C) → bridging (300-350 °C) → ionic (400-500 °C). The oxide powder resulted from the calcination of the gel at 800 °C is an assembly of mesoporous nanoparticles with uniform sizes, but agglomerated in lumps. It was confirmed that the chemical homogeneity, nanoparticle size uniformity and crystallinity, sinterability and electrical conductivity of (ZrO₂)_0.85(REO_1.5)_0.15 can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels.     

Luminescence of Ba3SrM2O9 (M = Nb,Ta)

The Nb₂O₉^8? and Ta₂O₉^8? complexes show efficient luminescence at low temperatures in Ba₃SrM₂O₉ (M = Nb, Ta). This is in line with earlier predictions. Emission and excitation spectra are reported and discussed. The Cr³⁺ ion in these complexes shows ²E emission. Its crystal field is strong. It is shown that CrNbO₉^10? and CrTaO₉^10? complexes are responsible for the spectra observed.     

Crystal Structure of Tl2[(UO2)2(MoO4)3] and Crystal Chemistry of the Compounds M2[(UO2)2(MoO4)3] (M = Tl, Rb, Cs)

A new compound, Tl₂[(UO₂)₂(MoO₄)₃], was prepared by a solid-phase reaction. The compound crystallizes in a rhombic system, space group Pna2₁, a = 20.1296(9), b = 8.2811(4), c = 9.7045(4), V = 1617.69(13) ų, Z = 4. The crystal structrue was solved by the direct method and refined to R ₁ = 0. 04 for 4884 unique reflections. The structural motif is a framework consisting of UO₇ pentagonal bipyramids and MoO₄ tetrahedra. The Tl coordination polyhedra are irregular, with seven and eight vertices. Large channels of the size 6 × 10.8 Å, occupied by Tl⁺ cations, are arranged parallel to the [001] direction. The compound is isostructural to the previously described α-Cs₂(UO₂)₂(MoO₄)₃ and Rb₂(UO₂)₂ (MoO₄)₃. __________ Translated from Radiokhimiya, Vol. 47, No. 5, 2005, pp. 408–411. Original Russian Text Copyright ? 2005 by Nazarchuk, Krivovichev, Burns.     

Crystal structure and ionic conductivity of ruthenium diphosphate ARu2(P2O7)2, A=Li, Na, and Ag, with a tunnel structure

Crystal structure and ionic conductivity of ruthenium diphosphates, ARu₂(P₂O₇)₂ A=Li, Na, and Ag, were investigated. The structure of the Ag compound was determined by single crystal X-ray diffraction techniques. It crystallized in the triclinic space group P−1 with a=4.759(2) Å, b=6.843(2) Å, c=8.063(1) Å, α=90.44(2)°, β=92.80(2)°, γ=104.88(2)°, V=253.4(1) Å³. The host structure of it was composed of RuO₆ and P₂O₇ groups and formed tunnels running along the a-axis, in which Ag⁺ ions were situated. The ionic conductivities have been measured on pellets of the polycrystalline powders. The Li and Ag compounds showed the conductivities of 1.0×10⁻⁴ and 3.5×10⁻⁵ S cm⁻¹ at 150 °C, respectively. Magnetic susceptibility measurement of the Ag compound showed that it did not obey the Curie-Weiss law and the effective magnetic moment decreased as temperature decreased due to the large spin-orbital coupling effect of Ru⁴⁺ ions.     

Synthesis, magnetic and thermoelectric properties of Rh2MO6 (M = Mo, Te, and W) with rutile-related structure

The Rh₂MO₆ compounds with M = Mo, W and Te were synthesized by solid state reaction. The compounds all crystallize in a rutile-type structure. These compounds would be expected to be diamagnetic insulators if the oxidation states were Rh³⁺ and M⁶⁺. In fact, all show relatively high electronic conductivities with Rh₂TeO₆ showing the highest electronic conductivity of ∼500 S/cm at room temperature. Measurable magnetic moments also indicate valence degeneracy between Rh and the M cation. The measured Seebeck coefficients are relatively low and positive indicating hole-type conduction.