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1.
In a series of investigations on normal tetrahedral compounds we present mixed crystals in the system Cu2MnxCo1?xGeS4 (0 < x < 1) and an inspection of their tetrahedra volumes. Cu2CoGeS4 crystallizes tetragonal in a stannite type structure, Cu2MnGeS4 crystallizes orthorhombic in the wurtzstannite structure type. The crystal structures of Cu2CoGeS4 and Cu2Mn0.68Co0.32GeS4 were refined from single crystal diffraction data. The refinement of Cu2CoGeS4 converged to R = 0.0547 and wR2 = 0.0847 for 299 unique reflections. The refinement of Cu2Mn0.68Co0.32GeS4 converged to R = 0.0481 and wR2 = 0.0877 for 1556 unique reflections. From these data the tetrahedra volumes of the end members and of Cu2Mn0.68Co0.32GeS4 are calculated. In Cu2CoGeS4 tetrahedra [MS4] are similar in size. In contrast, the differences of the volumes of the polyhedra [MS4] in the orthorhombic wurtzite superstructure type compounds Cu2MnGeS4 and Cu2Mn0.68Co0.32GeS4 are significant (M = Cu, Mn, (Mn0.68Co0.32), Co, Ge). From x = 0 to x = 0.5 the tetragonal structure type dominates while from x = 0.7 to the Cu2MnGeS4 end member the products crystallize in the orthorhombic structure type. Melting points of the mixed crystals decrease linearly with increasing manganese content.  相似文献   

2.
The cation ordering in the fluorite-like transparent conductors In4+xSn3−2xSbxO12 and In6TeO12, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb7O12-type structure with a strong preference of the smaller 4d10 cations (Sn4+, Sb5+, Te6+) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM4 tetrahedral network of the antistructure. The relationships between the M7O12 and the M2O3 bixbyite-type structures are explored. Within the whole series of compositions In4+xM3−xO12 (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M7O12 type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb.  相似文献   

3.
A structural, magnetic and electronic study of the cobaltocuprate CoSr2Y2−xCexCu2Oδ (x=0.5-0.8) has been performed. All materials crystallise in the orthorhombic Cmcm symmetry space group in which chains of corner linked CoO4 tetrahedra run parallel to the 1 1 0 direction. An antiferromagnetic transition is observed for x=0.5-0.8; TM increases with x. A change in the dimensionality of the magnetic order occurs at x=0.8 as the interchain distance increases to a critical value. There is charge transfer between the cuprate planes and cobaltate layer as Ce doping increases, so that Co3+ is partially oxidised to Co4+ with a concomitant reduction in the valence of Cu. Superconductivity is not observed in any of the samples and a crossover from Mott to Efros and Shklovskii variable range hopping behaviour is evidenced as x increases from 0.5 to 0.8.  相似文献   

4.
New ternary antimonide Dy3Cu20+xSb11−x (x≈2) was synthesized and its crystal structure was determined by direct methods from X-ray powder diffraction data (diffractometer DRON-3M, CuKα-radiation, RI=6.99%,Rp=12.27%,Rwp=11.55%). The compound crystallizes with the own cubic structure type: space group , Pearson code cF272, . The structure of the Dy3Cu20Sb11−x (x≈2) can be obtained from the structure type BaHg11 by doubling of the lattice parameter and subtraction of 16 atoms. The studied structure was compared with the structures of known compounds, which crystallize in the same space group with similar cell parameters.  相似文献   

5.
6.
Solid solutions SrAuxIn4−x (0.5?x?1.2) and SrAuxSn4−x (1.3?x?2.2) have been prepared at 700 °C and their structures characterized by powder and single-crystal X-ray diffraction. They adopt the tetragonal BaAl4-type structure (space group I4/mmm, Z=2; SrAu1.1(1)In2.9(1), a=4.5841(2) Å, c=12.3725(5) Å; SrAu1.4(1)Sn2.6(1), a=4.6447(7) Å, c=11.403(2) Å), with Au atoms preferentially substituting into the apical over basal sites within the anionic network. The phase width inherent in these solid solutions implies that the BaAl4-type structure can be stabilized over a range of valence electron counts (vec), 13.0-11.6 for SrAuxIn4−x and 14.1-11.4 for SrAuxSn4−x. They represent new examples of electron-poor BaAl4-type compounds, which generally have a vec of 14. Band structure calculations confirm that substitution of Au, with its smaller size and fewer number of valence electrons, for In or Sn atoms enables the BaAl4-type structure to be stabilized in the parent binaries SrIn4 and SrSn4, which adopt different structure types.  相似文献   

7.
Phase relations in the ternary systems Ce-M-Sb (M=Si, Ge, Sn) in composition regions CeSb2-Sb-M were studied by optical and electron microscopy, X-ray diffraction, and electron probe microanalysis on arc-melted alloys and specimens annealed in the temperature region from 850 to 200 °C. The results, in combination with an assessment of all literature data available, were used to construct solidus surfaces and a series of isothermal sections. No ternary compounds were found to form in the Ce-Si-Sb system whilst Ce12Ge9−xSb23+x (3.3<x<4.2) and CeSnxSb2 (0.1<x<0.8) participate in phase equilibria in the composition region investigated. Crystallographic parameters for the ternary compound Ce12Ge9−xSb23+x (x=3.8±0.1) were determined from X-ray single crystal and powder diffraction. For the binary system Ge-Sb a eutectic was defined L⇔(Ge)+(Sb) at 591.6 °C and 22.5 at%. Ge EPMA revealed a maximal solubility of 6.3 at% Ge in (Sb) at the eutectic temperature.  相似文献   

8.
The local structure of In2O3 cosubstituted with Zn and Sn (In2−2xSnxZnxO3, x≤0.4 or ZITO) was determined by extended X-ray absorption fine structure (EXAFS) for x=0.1, 0.2, 0.3 and 0.4. The host bixbyite In2O3 structure is maintained up to the enhanced substitution limit (x=0.4). The EXAFS spectra are consistent with random substitution of In by the smaller Zn and Sn cations, a result that is consistent with the “good-to-excellent” conductivities reported for ZITO.  相似文献   

9.
A comparative study of two Sn-based composite materials as negative electrode for Li-ion accumulators is presented. The former SnB0.6P0.4O2.9 obtained by in-situ dispersion of SnO in an oxide matrix is shown to be an amorphous tin composite oxide (ATCO). The latter Sn0.72[BPO4]0.28 obtained by ex-situ dispersion of Sn in a borophosphate matrix consists of Sn particles embedded in a crystalline BPO4 matrix. The electrochemical responses of ATCO and Sn0.72[BPO4]0.28 composite in galvanostatic mode show reversible capacities of about 450 and 530 mAh g−1, respectively, with different irreversible capacities (60% and 29%). Analysis of these composite materials by 119Sn Mössbauer spectroscopy in transmission (TMS) and emission (CEMS) modes confirms that ATCO is an amorphous SnII composite oxide and shows that in the case of Sn0.72[BPO4]0.28, the surface of the tin clusters is mainly formed by SnII in an amorphous interface whereas the bulk of the clusters is mainly formed by Sn0. The determination of the recoilless free fractions f (Lamb-Mössbauer factors) leads to the effective fraction of both Sn0 and SnII species in such composites. The influence of chemical composition and especially of the surface-to-bulk tin species ratio on the electrochemical behaviour has been analysed for several Snx[BPO4]1−x composite materials (0.17<x<0.91). The cell using the compound Sn0.72[BPO4]0.28 as active material exhibits interesting electrochemical performances (reversible capacity of 500 mAh g−1 at C/5 rate).  相似文献   

10.
The compounds Bi6+xT1−xP2O15+y, T=Ti, Cr, Mn, Fe, Co, Ni, Cu, Zn and Pb display five polymorphic forms. Polymorph A is formed by the Ti, Mn, Fe and Ni phases. Polymorph B is exhibited by Co and Cu compounds. The Cr phase crystallizes as polymorphic form C and the Zn phase crystallizes as polymorph D. The Pb compound crystallizes in a new structure type designated as polymorph E. The transition metal crystal structures demonstrate a similar motive. OBi4 tetrahedra share edges to form two-dimensional Bi2O2 layers that are spanned by PO4 tetrahedra and TO6−y octahedra, pyramids and a trigonal bipyramid to form a three-dimensional network. Polymorph A crystallizes in space group C2; polymorph B is centrosymmetric with space group C2/c, the unit cell parameters differ and the unit cell volume is about double. Polymorph C crystallizes in space group and polymorph D exhibits space group C2. Bi6.4Pb0.6P2O15.2 can be considered as polymorph E, space group C2, with a new crystal structure but related stoichiometry.  相似文献   

11.
The crystal structure of the promising optical materials Ln2M2+Ge4O12, where Ln=rare-earth element or Y; M=Ca, Mn, Zn and their solid solutions has been studied in detail. The tendency of rare-earth elements to occupy six- or eight-coordinated sites upon iso- and heterovalent substitution has been studied for the Y2−xErxCaGe4O12 (x=0-2), Y2−2xCexCa1+xGe4O12 (x=0-1), Y2Ca1−xMnxGe4O12 (x=0-1) and Y2−xPrxMnGe4O12 (x=0-0.5) solid solutions. A complex heterovalent state of Eu and Mn in Eu2MnGe4O12 has been found.  相似文献   

12.
The synthesis of a new potassium titanosilicate, K4Ti2Si6O18 (Ti-AV-11), possessing the crystal structure of potassium stannosilicate AV-11, has been reported. The unit cell of this material is trigonal, space group R3 (no. 146), Z=3, a=10.012, c=14.8413 Å, γ=120°, V=1289 Å3. The structure of AV-11 is built up of MO6 (M=Sn, Ti) octahedra and SiO4 tetrahedra by sharing corners. The SiO4 tetrahedra form helix chains, periodically repeating every six tetrahedra. These chains extend along the [001] direction and are linked by isolated MO6 octahedra, thus producing a mixed octahedral-tetrahedral oxide framework. AV-11 materials have been further characterized by bulk chemical analysis, powder X-ray diffraction (XRD), scanning electron microscopy (SEM), 29Si and 119Sn magic-angle spinning (MAS) NMR spectroscopy.  相似文献   

13.
Yb3Cu6Sn5, Yb5Cu11Sn8 and Yb3Cu8Sn4 compounds were prepared in sealed Ta crucibles by induction melting and subsequent annealing. The crystal structures of Yb3Cu6Sn5 and Yb5Cu11Sn8 were determined from single crystal diffractometer data: Yb3Cu6Sn5, isotypic with Dy3Co6Sn5, orthorhombic, Immm, oI28, a=4.365(1) Å, b=9.834(3) Å, c=12.827(3) Å, Z=2, R=0.019, 490 independent reflections, 28 parameters; Yb5Cu11Sn8 with its own structure, orthorhombic, Pmmn, oP48, a=4.4267(6) Å, b=22.657(8) Å, c=9.321(4) Å, Z=2, R=0.047, 1553 independent reflections, 78 parameters. Both compounds belong to the BaAl4-derived defective structures, and are closely related to Ce3Pd6Sb5 (oP28, Pmmn). The crystal structure of Yb3Cu8Sn4, isotypic with Nd3Co8Sn4, was refined from powder data by the Rietveld method: hexagonal, P63mc, hP30, a=9.080(1) Å, c=7.685(1) Å, Z=2, Rwp=0.040. It is an ordered substitution derivative of the BaLi4 type (hP30, P63/mmc). All compounds show strong Cu-Sn bonds with a length reaching 2.553(3) Å in Yb5Cu11Sn8.  相似文献   

14.
The composition range and (composite modulated) structure of compounds within the wide range non-stoichiometric LaSb2Snx, 0.1?x?0.75, solid solution is carefully investigated via a combined electron diffraction, XRD and electron probe microanalysis study. Evidence for metastability of the LaSb2Snx phase at the low x composition end of the solid solution is presented. Direct evidence is found for a reasonably (although by no means perfectly) well ordered Sn sub-structure which is, in general, mutually incommensurable with respect to a very well ordered underlying LaSb2 sub-structure along both a and c directions. The overall (3+2)-d superspace group symmetry is given along with a discussion of the consequences as regards the arrangement of the Sn atoms. The Sn sub-structure c-axis cell dimension shows very little variation with composition x providing direct experimental evidence of the importance of Sn-Sn metallic bonding (along one-dimensional [001] Sn strings) for the stability of the phase.  相似文献   

15.
The three new ternary phases Na16Zn13.54Sn13.46(5) (I), Na22Zn20Sn19(1) (II), and Na34Zn66Sn38(1) (III) were obtained by direct fusion of the pure elements and characterized by single crystal X-ray diffraction experiments: I, Ibam, Z=8, a=27.401(1), b=16.100(1), c=18.431(1) Å, R1/wR2 (all data)=0.051/0.088; II, Pnma, Z=4, a=16.403(1), b=15.598(1), c=22.655(6) Å, R1/wR2 (all data)=0.038/0.071; III, Rm, Z=3, a=16.956(1), c=36.861(1) Å, R1/wR2 (all data)=0.045/0.092. The structures consist of complex 3D cluster networks made of Zn and Sn atoms with the common motif of Kagomé nets of icosahedra. Additionally to the new heteroatomic {Zn12−xSnx} icosahedra that are omnipresent, triangular units, cages, and pairs of triply fused icosahedra fill the cavities of the Kagomé nets in compounds I, II, and III, respectively. Whereas I crystallizes in a new structure type, II and III have structural analogs in trielide chemistry. All three compounds closely approach the electron numbers expected for valence compounds according to the extended 8-N rule. The concept of achieving an isovalent situation to triel elements by combination of electron poorer and richer elements and the readily mixing of Zn and Sn allow the formation of icosahedral and triangular clusters without the participation of a group 13 element.  相似文献   

16.
A tin(II) squarate Sn2O(C4O4)(H2O) was synthesized by hydrothermal technique. It crystallizes in the monoclinic system, space group C2/m (no. 12) with lattice parameters a=12.7380(9) Å, b=7.9000(3) Å, c=8.3490(5) Å, β=121.975(3)°, V=712.69(7) Å3, Z=4. The crystal structure determined with an R=0.042 factor, consists of [(Sn4O10)(H2O)2] units connected from one another in the [101] and [010] directions via squarate groups to form layers separated by Sn(II) lone pairs. This compound presents the same remarkable structural arrangement as observed in the tin-oxo-fluoride Sn2[Sn2O2F4] inorganic compound with Sn(II) lone pairs E(1) and E(2) concentrated in large rectangular-shape tunnels running along [001] direction.  相似文献   

17.
Bi6.4Pb0.6P2O15.2 is a polymorph of structures with the general stoichiometry Bi6+xM1−xP2O15+y. However, unlike previously published structures that consist of layers formed by edge sharing OBi4 tetrahedra bridged by PO4 and TO6 (T=transition metal) tetrahedra and octahedra the title compound's structure is more complex. It is monoclinic, C2, a=19.4698(4) Å, b=11.3692(3) Å, c=16.3809(5) Å, β=101.167(1)°, Z=10. Single-crystal X-ray diffraction data were refined by least squares on F2 converging to R1=0.0387, wR2=0.0836 for 7023 intensities. The crystal twins by mirror reflection across (001) as the twin plane and twin component 1 equals 0.74(1). Oxygen ions are in tetrahedral coordination to four metal ions and the O(BiPb)4 units share corners to form layers that are part of the three-dimensional framework. Eight oxygen ions form a cube around the two crystallographically independent Pb ions. Pb-O bond lengths vary from 2.265(14) to 2.869(14) Å. Pairs of such cubes share an edge to form a Pb3O20 unit. The two oxygen ions from the unshared edges are part of irregular Bi polyhedra. Other oxygen ions of Bi polyhedra are part only of O(BiPb)4 units, and some oxygen ions of the polyhedra are also part of PO4 tetrahedra. One, two, three and or four PO4 moieties are connected to the Bi polyhedra. Bi-O bond lengths ?3.1 Å vary from 2.090(12) to 3.07(3) Å. The articulations of Pb cubes, Bi polyhedra and PO4 tetrahedra link into the three-dimensional structure.  相似文献   

18.
19.
A combination of electron, synchrotron X-ray and neutron powder diffraction reveals a new orthorhombic structure type within the Sr-doped rare earth perovskite cobaltates Ln1−xSrxCoO3−δ (Ln=Y3+, Dy3+, Ho3+, Er3+, Tm3+and Yb3+). Electron diffraction shows a C-centred cell based on a 2√2ap×4ap×4√2ap superstructure of the basic perovskite unit. Not all of these very weak satellite reflections are evident in the synchrotron X-ray and neutron powder diffraction data and the average structure of each member of this series could only be refined based on Cmma symmetry and a 2√2ap×4ap×2√2ap cell. The nature of structural and magnetic ordering in these phases relies on both oxygen vacancy and cation distribution. A small range of solid solution exists where this orthorhombic structure type is observed, centred roughly around the compositions Ln0.2Sr0.8CoO3−δ. In the case of Yb3+ the pure orthorhombic phase was only observed for 0.850?x?0.875. Tetragonal (I4/mmm; 2ap×2ap×4ap) superstructures were observed for compositions having higher or lower Sr-doping levels, or for compounds with rare earth ions larger than Dy3+. These orthorhombic phases show mixed valence (3+/4+) cobalt oxidation states between 3.2+ and 3.3+. DC magnetic susceptibility measurements show an additional magnetic transition for these orthorhombic phases compared to the associated tetragonal compounds with critical temperatures > 330 K.  相似文献   

20.
We show that Rh substitution at the Co site in Zr0.5Hf0.5Co1−xRhxSb0.99Sn0.01 (0≤x≤1) half-Heusler alloys strongly reduces the thermal conductivity with a simultaneous, significant improvement of the power factor of the materials. Thermoelectric properties of hot-pressed pellets of several compositions with various Rh concentrations were investigated in the temperature range from 300 to 775 K. The Rh “free” composition shows n-type conduction, while Rh substitution at the Co site drives the system to p-type semiconducting behavior. The lattice thermal conductivity of Zr0.5Hf0.5Co1−xRhxSb0.99Sn0.01 alloys rapidly decreased with increasing Rh concentration and lattice thermal conductivity as low as 3.7 W/m*K was obtained at 300 K for Zr0.5Hf0.5RhSb0.99Sn0.01. The drastic reduction of the lattice thermal conductivity is attributed to mass fluctuation induced by the Rh substitution at the Co site, as well as enhanced phonon scattering at grain boundaries due to the small grain size of the synthesized materials.  相似文献   

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