首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 46 毫秒
1.
We report the synthesis and elementary properties of the Co7Se8−xSx (x=0-8) and Ni7Se8−xSx (x=0-7) solid solutions. Both systems form a NiAs-type structure with metal vacancies. In general, the lattice parameters decrease with increasing x, but in the Ni7Se8−xSx system c increases on going from x=5 to 7. Magnetic susceptibility measurements show that all samples exhibit temperature-independent paramagnetism from 25-250 K. Samples within the Co7Se8−xSx system, as well as Ni7Se8 and Ni7SeS7, were found to be poor metals with resistivities of ∼0.20 and ∼0.06 mΩ cm at 300 K, respectively. The Sommerfeld constant (γ) was determined from specific heat measurements to be ∼13 mJ/molCoK2 and ∼7 mJ/molNiK2 for Co7Se8−xSx and Ni7Se8−xSx, respectively.  相似文献   

2.
Layered compounds have been synthesized and structurally characterized for the n=5 and 6 members of the perovskite-related family La4Srn−4TinO3n+2 by combining X-ray diffraction and transmission electron microscopy. Their structure can be regarded as comprising [(La,Sr)5Ti5O17] and [(La,Sr)6Ti6O20] perovskite blocks joined by crystallographic shears along the a-axis, with consecutive blocks shifted by 1/2 [100]p. The n=5 member is similar to the previously reported n=5 member of other AnBnO3n+2-related series. The n=6 member, which has only been briefly reported in other systems previously, is also a well-behaved member of this AnBnO3n+2 series.  相似文献   

3.
The actual oxygen environment of the tungsten dopant in the Ba2In2−xWxO5+3x/2 solid solution was revealed by combining X-ray absorption spectroscopy at the tungsten LI and LIII edges and at the indium LI edge. Whatever the substitution ratio, the tungsten atoms exhibit a regular octahedral environment. When the substitution ratio increases, the oxygen vacancies are progressively filled until their total occupancy for x=2/3. For x?0.3, the perovskite structure is stabilised; the tungsten atoms are randomly distributed in the structure. Although X-ray diffraction revealed a cubic symmetry for these compositions, a local distortion of the indium environment is observed when a tungsten atom is in its surrounding.  相似文献   

4.
A new direct route for the “bottom up” syntheses of phases in the Lan+1NinO3n+1 series (n=1, 2, 3 and ∞) has been achieved via single-step heat treatments of nanosized co-crystallized precursors. The co-crystallized precursors were prepared using a continuous hydrothermal flow synthesis system that uses a superheated water flow at ca. 400 °C and 24.1 MPa to produce nanoparticulate slurries. Overall, a significant reduction in time and number of steps for the syntheses of La3Ni2O7 and La4Ni3O10 was achieved compared with more conventional synthesis methods, which typically require multiple homogenization and reheating steps over several days.  相似文献   

5.
The solid solutions of ScBRh3-ScRh3 and CeBRh3-CeRh3 are synthesized by the arc melting method, where RBRh3 and RRh3 (R=rare earth element) have perovskite and AuCu3 type structures, respectively. The binding energy of Sc 2p3/2 for ScBxRh3 increases with the boron concentration. The Knight shift of 45Sc observed by nuclear magnetic resonance spectroscopy decreases with increase of boron concentration. The decrement of the Knight shift corresponds the Sc 4s electron density at the Fermi level. The intensity ratio of f2f1f0 of Ce 3d XPS spectrum changes with boron concentration of CeBxRh3. It is concluded that in both cases of ScBxRh3 and CeBxRh3 the charge on the atoms on A-site changes with the concentration of the atoms on B-site, where the atoms are not directly bound.  相似文献   

6.
A series of lithium europium double tungsto-molybdate phosphors LiEu(WO4)2−x(MoO4)x (x=0, 0.4, 0.8, 1.2, 1.6, 2.0) have been synthesized by solid-state reactions and their crystal structure, optical and luminescent properties were studied. As the molybdate content increases, the intensity of the 5D07F2 emission of Eu3+ activated at wavelength of 396 nm was found to increase and reach a maximum when the relative ratio of Mo/W is 2:0. These changes were found to be accompanied with the changes in the spectral feature, which can be attributed to the crystal field splitting of the 5D07F2 transition. As the molybdate content increases the emission intensity of the 615 nm peak also increases. The intense red-emission of the tungstomolybdate phosphors under near-UV excitation suggests them to be potential candidate for white light generation by using near-UV LEDs. In this study the effect of chemical compositions and crystal structure on the photoluminescent properties of LiEu(WO4)2−x(MoO4)x is investigated and discussed.  相似文献   

7.
The synthesis, structure, and physical properties of five R-type Ru ferrites with chemical formula BaMRu5O11 (M=Li and Cu) and BaM2Ru4O11 (M′=Mn, Fe and Co) are reported. All the ferrites crystallize in space group P63/mmc and consist of layers of edge sharing octahedra interconnected by pairs of face sharing octahedra and isolated trigonal bipyramids. For M=Li and Cu, the ferrites are paramagnetic metals with the M atoms found on the trigonal bipyramid sites exclusively. For M′=Mn, Fe and Co, the ferrites are soft ferromagnetic metals. For M′=Mn, the Mn atoms are mixed randomly with Ru atoms on different sites. The magnetic structure for BaMn2Ru4O11 is reported.  相似文献   

8.
A systematic study of the chemical interaction of Ba2YCu3O6+y and Gd3NbO7 was conducted under two processing conditions: purified air (21% po2), and 100 Pa po2 (0.1% po2). Phases present along the pseudo-binary join Ba2YCu3O6z and Gd3NbO7 were found to be in two five-phase volumes within the system. Three common phases that are present in all samples are (Y,Gd)2Cu2O5, Ba(Y,Gd)2CuO5 and Cu2O or CuO (depending on the processing conditions). The assemblies of phases can be categorized in three regions, with Ba2YCu3O6+y: Gd3NbO7 ratios of (I)<5.5:4.5; (II)=5.5:4.5; and (III)>5.5:4.5. The lowest melting temperature of the system was determined to be ≈938 °C in air, and 850 °C at 100 Pa po2. Structure determinations of two selected phases, Ba2(GdxY1−x)NbO6 (Fmm, No. 225), and (GdxY3−x)NbO7 (C2221, No. 20 and Ccmm, No. 63), were completed using the X-ray Rietveld refinement technique. Reference X-ray powder diffraction patterns for selected phases of Ba2(GdxY1−x)NbO6 (x=0.2, 0.4, 0.6, and 0.8) and (GdxY3−x)NbO7 (x=0.6, 1.2, 1.8, 2.4 and 3) have been prepared for inclusion in the Powder Diffraction File (PDF).  相似文献   

9.
Oxides in the system PrCo1−xMgxO3 (x=0.0, 0.05, 0.10, 0.15, 0.20, 0.25) were synthesized by citrate technique and characterized by powder X-ray diffraction and scanning electron microscope. All compounds have a cubic perovskite structure (space group ). The maximum ratio of doped Mg in the system PrCo1−xMgxO3 is x=0.2. Further doping leads to the segregation of Pr6O11 in PrCo1−xMgxO3. The substitution of Mg for Co improves the performance of PrCoO3 as compared to the electrical conductivity measured by a four-probe electrical conductivity analyzer in the temperature range from 298 to 1073 K. The substitution of Mg for Co on the B site may be compensated by the formations of Co4+ and oxygen vacancies. The electrical conductivity of PrCo1−xMgxO3 oxides increases with increasing x in the range of 0.0-0.2. The increase in conductivity becomes considerable at the temperatures ?673 K especially for x?0.1; it reaches a maximum at x=0.2 and 1073 K. From x>0.2 the conductivity of PrCo1−xMgxO3 starts getting lower. This is probably a result of the segregation of Pr6O11 in PrCo1−xMgxO3 , which blocks oxygen transport, and association of oxygen vacancies. A change in activation energy for all PrCo1−xMgxO3 compounds (x=0-0.25) was observed, with a higher activation energy above 573 K and a lower activation energy below 573 K. The reasons for such a change are probably due to the change of dominant charge carriers from Co4+ to Vö in PrCo1−xMgxO3 oxides and a phase transition mainly starting at 573 K.  相似文献   

10.
The crystal structures of ternary compounds RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt3−xSi1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt3−xSi1−y can be considered as a packing of four types of building blocks which derive from the CePt3B-type unit cell by various degrees of distortion and Pt, Si-defects.  相似文献   

11.
Zr1−xLnxW2O8−x/2 solid solutions (Ln=Eu, Er, Yb) of different substitution fractions x have been synthesized. Their X-ray diffraction (XRD) patterns have been indexed and lattice parameters calculated based on the α-ZrW2O8 structure. The coefficients of thermal expansion (CTEs) of these solid solutions were estimated to be −10.3×10−6 K−1 in temperature range of 30-100 °C. The solubility of lanthanide ions in these solid solutions decreases linearly with the increase in the radius of substituted lanthanide ions. Based on the concentration dependence of phase transition temperatures, a novel method for determination of solubility of the lanthanide ions in Zr1−xLnxW2O8−x/2 solid solutions has been developed. This method seems to be more sensitive as compared with that based on XRD technique.  相似文献   

12.
A-site substituted cerium orthovanadates, Ce1−xSrxVO4, were synthesised by solid-state reactions. It was found that the solid solution limit in Ce1−xSrxVO4 is at x=0.175. The crystal structure was analysed by X-ray diffraction and it exhibits a tetragonal zircon structure of space group I41/amd (1 4 1) with a=7.3670 (3) and c=6.4894 (1) Å for Ce0.825Sr0.175VO4. The UV-vis absorption spectra indicated that the compounds have band gaps at room temperature in the range 4.5-4.6 eV. Conductivity measurements were performed for the first time up to the strontium solid solution limit in air and in dry 5% H2/Ar with conductivity values at 600 °C ranging from 0.3 to 30 mS cm−1 in air to 30-45 mS cm−1 in reduced atmosphere. Sample Ce0.825Sr0.175VO4 is redox stable at a temperature below 600 °C although the conductivity is not high enough to be used as an electrode for solid oxide fuel cells.  相似文献   

13.
The structure of pseudorhombohedral-type InFe1−xTixO3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO3-In2Ti2O7 including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P21/a is the alternate stacking of an edge-shared InO6 octahedral layer and an Fe/Ti-O plane along c*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10−4 S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.  相似文献   

14.
Ag-doped n-type (Bi2Te3)0.9-(Bi2−xAgxSe3)0.1 (x=0-0.4) alloys were prepared by spark plasma sintering and their physical properties evaluated. When at low Ag content (x=0.05), the temperature dependence of the lattice thermal conductivity follows the trend of (Bi2Te3)0.9-(Bi2Se3)0.1; while at higher Ag content, a relatively rapid reduction above 400 K can be observed due possibly to the enhancement of scattering of phonons by the increased defects. The Seebeck coefficient increases with Ag content, with some loss of electrical conductivity, but the maximum dimensionless figure of merit ZT can be obtained to be 0.86 for the alloy with x=0.4 at 505 K, about 0.2 higher than that of the alloy (Bi2Te3)0.9-(Bi2Se3)0.1 without Ag-doping.  相似文献   

15.
Intercalation behavior of n-alkylamines into a protonated form of an A-site defective layered perovskite H2W2O7 has been investigated. Results from XRD indicate these materials are layered with the corresponding interlayer spacing governed by the n-alkylamine chain length, and a reversible intercalation and deintercalation property is observed among these intercalation compounds. The IR spectra of the intercalation compounds with n-alkylamines clearly show that n-alkyl chains possess an all-trans conformation, and H2W2O7 accommodate n-alkylamines (CnH2n+1NH2: n=3, 4, 7, 8, 12, 16) to form intercalation compounds via an acid-base mechanism. A linear relationship between the interlayer distance and the number of carbon atoms in n-alkyl chains is observed to show a bilayer arrangement of the n-alkyl chains with a tilt angle of ∼71.6°. Elemental analysis studies reveal that the amounts of intercalated n-alkylamines are about 2.0 mol per [W2O7]. Despite the surface geometry of H2W2O7 is almost identical to those of layered perovskites H2[An−1BnO3n+1], the amounts of intercalated n-alkylamines of them are different. A reasonable explanation is given through our research.  相似文献   

16.
Cathode materials Li[CoxMn1−x]O2 for lithium secondary batteries have been prepared by a new route—precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass spectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH·H2O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li+ into the lattice, resulting in the formation of layered Li[CoxMn1−x]O2 with α-NaFeO2 structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[CoxMn1−x]O2, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[CoxMn1−x]O2 have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAh g−1 for the layered material Li[Co0.80Mn0.20]O2.  相似文献   

17.
The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca14−xRxCu24O41 (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2−xCu5O10 (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca14−xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14−xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2−xCu5O10 solid solution is isostructural to Ca2+xY2−xCu5O10, the structure of which is based on an orthorhombic “NaCuO2-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.  相似文献   

18.
Various compositions of solid solutions K3P(Mo1−xWx)12O40 (0?x?1) were prepared using two solid state synthetic routes. The crystallite size was determined by linewidth refinements of X-ray diffraction patterns using the Warren-Averbach method, and the grain size distribution by laser scattering experiments. Optical properties were determined by diffuse reflectance measurements in the UV-visible range. The optical gap Eg was found to increase exponentially from ∼2.5 to ∼3.30 eV with increasing x, and is systematically shifted to a higher energy when the grain size decreases. The relation between Eg and x was analyzed by calculating the HOMO-LUMO gaps of the [P(Mo1−xWx)12O40]3− anions on the basis of tight-binding electronic structure calculations.  相似文献   

19.
A novel quaternary scandium borocarbosilicide Sc3.67−xB41.4−yzC0.67+zSi0.33−w was found. Single crystallites were obtained as an intergrowth phase in the float-zoned single crystal of Sc0.83−xB10.0−yC0.17+ySi0.083−z that has a face-centered cubic crystal structure. Single crystal structure analysis revealed that the compound has a hexagonal structure with lattice constants a = b = 1.43055(8) nm and c = 2.37477(13) nm and space group (No. 187). The crystal composition calculated from the structure analysis for the crystal with x = 0.52, y = 1.42, z = 1.17, and w = 0.02 was ScB12.3C0.58Si0.10 and that agreed rather well with the composition of ScB11.5C0.61Si0.04 measured by EPMA. In the crystal structure that is a new structure type of boron-rich borides, there are 79 structurally independent atomic sites, 69 boron and/or carbon sites, two silicon sites and eight scandium sites. Boron and carbon form seven structurally independent B12 icosahedra, one B9 polyhedron, one B10 polyhedron, one irregularly shaped B16 polyhedron in which only 10.7 boron atoms are available because of partial occupancies and 10 bridging sites. All polyhedron units and bridging site atoms interconnect each other forming a three-dimensional boron framework structure. Sc atoms reside in the open spaces in the boron framework structure.  相似文献   

20.
Cubic ZrW2−xMoxO8 (c-ZrW2−xMoxO8) (x=0-1.3) solid solutions were prepared by a novel polymorphous precursor transition route. X-ray diffraction (XRD) analysis reveals that the solid solutions are single phase with α- and β-ZrW2O8 structure for 0?x?0.8 and 0.9?x?1.3, respectively. The optimum synthesis conditions of ZrWMoO8 are obtained from differential scanning calorimetry-thermal gravimetric analysis (DSC-TGA), XRD and mass loss-temperature/time curves. Following the above experience, the stoichiometric solid solutions of c-ZrW2−xMoxO8 (x=0-1) are obtained within 1 wt% of mass loss. The relationships of lattice parameters (a), phase transition temperatures (Tc) and instantaneous coefficients of thermal expansion (αi) against the content x of Mo are discussed based on the variation of order degree parameters of ZrW2−xMoxO8.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号