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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. 相似文献
3.
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). 相似文献
4.
《Materials Research Bulletin》1987,22(3):331-336
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. 相似文献
5.
Shuaihang Qiu Huimin Xiang Fu-Zhi Dai Hailong Wang Muzhang Huang Chunlei Wan Qing Meng Jiangtao Li Xiaohui Wang Yanchun Zhou 《材料科学技术学报》2022,(28):144-153
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 ... 相似文献
6.
New Pb-based superconducting cuprate with the 1201 structure has been synthesized in the (Pb1 − yBy)(Sr2 − xLax)CuOz 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 (Pb1 − yBy)(Sr2 − xLax)CuOz. 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. 相似文献
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P. Lejay B. Chevalier J. Etourneau J.M. Tarascon P. Hagenmuller 《Materials Research Bulletin》1983,18(1):67-71
New superconducting materials have been prepared by substitution of silicon by Rh or Ir atoms in the α-ThSi2 disilicide. The ThMxSi2?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 Tcr is observed for x > 0.75 in both cases. Among the superconducting compounds with an α-ThSi2-type structure, ThRh0.96Si1.04 and ThIrSi have the highest Tcr values with respectively 6.45 and 6.5 K about twice that of α-ThSi2 (Tcr = 3.16 K). Superconductivity enhancement has been attributed to the formation of Rh-Rh or Ir-Ir metallic type bonding. 相似文献
9.
Daniel Caurant Pascal Loiseau Isabelle Bardez Christel Gervais 《Journal of Materials Science》2007,42(20):8558-8570
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. 相似文献
10.
C. Delmas A. Maazaz F. Guillen C. Fouassier J.M. Réau P. Hagenmuller 《Materials Research Bulletin》1979,14(5):619-625
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. 相似文献
11.
Roger Chevrel Michel Potel Marcel Sergent Michel Decroux Oystein Fischer 《Materials Research Bulletin》1980,15(7):867-874
New superconducting MoII 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 (Tc = 3.32 K for K2Mo15S19), and have high initial slopes of the upper critical field. 相似文献
12.
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. 相似文献
13.
Erin E EricksonDanielle Gray Kathryn TaylorRobin T Macaluso Lee Ann LeTardG.S Lee Julia Y Chan 《Materials Research Bulletin》2002,37(13):2077-2083
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 Ln2Ti2-2xM2xO7 (Ln=Gd, Er; M=Zr, Sn, Si) systems were synthesized by ceramic methods and characterized by powder X-ray diffraction. The ZrO2-doped Gd2Ti2−2xZr2xO7 compounds adopt the pyrochlore structure type and form a complete solid solution. Er2Ti2−2xZr2xO7 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 Ln2Ti2−2xSn2xO7 (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 Er2Ti2−2xZr2xO7 and 16-31 for Gd2Ti2−2xZr2xO7 with low dielectric loss (1×10−3) at 1 GHz. 相似文献
14.
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 CaLa2S4La2S3 solid solutions, up to 10 mm3 volume, have been grown from the melt in sealed crucibles using the Stöber technique. 相似文献
15.
The phase diagrams of the chromium sulfide systems Cr1?xMxCr2S4, Cr1?xFexCr2S4, andCr1?xCoxCr2S4 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. 相似文献
16.
Ya-Wen Zhang 《Materials Research Bulletin》2004,39(11):1763-1777
By the citrate gel method, (ZrO2)0.85(REO1.5)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(REO1.5)0.15 can be remarkably improved by avoiding the phase separation (solid/liquid) phenomenon during the preparation of the gels. 相似文献
17.
The Nb2O98? and Ta2O98? 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 CrNbO910? and CrTaO910? complexes are responsible for the spectra observed. 相似文献
18.
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) Å3, 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.
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Translated from Radiokhimiya, Vol. 47, No. 5, 2005, pp. 408–411.
Original Russian Text Copyright ? 2005 by Nazarchuk, Krivovichev, Burns. 相似文献
19.
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. 相似文献
20.
Theeranun Siritanon Krishnendu Biswas Arthur W. Sleight M.A. Subramanian 《Materials Research Bulletin》2011,46(11):2016-2020
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. 相似文献