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1.
A series of isotypic silicates of composition RE2M[SiO4]2 (OH) with RE = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, and M = Al3+, Fe3+ has been synthesized under hydrothermal conditions. Lattice constants of two members as determined from single crystal X-ray diffraction data are: La2Al[SiO4]2 (OH) (La2Fe[SiO4]2 (OH)) ao = 7.401 (7.346) A?, bo = 5.702 (5.862) A?, co = 17.072 (97.196) A?, gb = 112.4 (112.5°), P21c, Z=4.  相似文献   

2.
Neutron diffraction experiments have been performed to determine the structures of Ba2LaRuO6 and Ca2LaRuO6. Both are ordered, distorted perovskites. Ba2LaRuO6 is monoclinic, space group P21n with a0=6.0285(7)A?, b0=6.0430(7)A?, c0=8.5409(6)A?, β=90.44(1)o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca2LaRuO6 is triclinic, space group P1 with a0=5.6179(5), b0=5.8350(5), c0=8.0667(4), α=90.0o, β=89.76(1)o, γ=90.0o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.  相似文献   

3.
Europium orthoborate and strontium orthoborate crystallize in the rhombohedral system with two formula units in a cell of dimensions aR=6.697 A?, αR=85.17° for Eu3B2O6, and aR=6.695 A?, αR=85.00° for Sr3B2O6. The equivalent hexagonal lattice parameters are aH=9.069 A?, cH=12.542 A?, and aH=9.046 A?, cH=12.566 A? respectively. Eu3B2O6 appears to be ferromagnetic below 7.5K.  相似文献   

4.
Tridimensional P2NbS8 crystallizes in P4?n2 tetragonal space group, with a = 12.0483(4) A?, c = 7.2070(5) A?, V = 1046.2(1) A?3 and Z = 4. The structure was anisotropically refined down to R = 2.3% from 468 reflexions and 53 variables. It is built from [Nb2S12] biprismatic bicapped units (average dNb?S = 2.571 A?) made of S?II and S?II2 anions (dianionic distance of 2.014(3) Å). The niobium atoms are found as isolated NbIV ? NbIV pairs (dNb?Nb = 2.859(1) A?) in these niobium group otherwise linked to each other through (PS4) tetrahedral units (average dP?S = 2.051 A?) themselves constituting interbonded [P4S12] rings. The P2NbS8 three-dimensional network thus obtained is compared to the (2D) P2NbS8, layered phase already described.  相似文献   

5.
The parameters for the structure of K2Cr2O7 have been refined from 7511 observed reflections; ao = 7.4200(6)A?, bo = 13.399(3)A?, co = 7.3845(9)A?, cosα = ?0.1396(2) (α = 98°2'), cosβ = ?0.0154(2) (β = 90°53'), cosγ = ?0.1078(2) (γ = 96°11'). The discrepancy factor R(Fo2) = 0.0702 with a type 2 extinction correction. The average CrO distances are 1.609Å (unshared) and 1.783Å (shared).  相似文献   

6.
The existence has been proved, for the first time, in the LaLiFeO system of the phase (La1.75Li.25) (Fe.5Li.5)O4?x with tetragonal symmetry (ao=3.765±0.001 A?; co=12.918±0.01 A?; coao=3.43) and K2NiF4-type structure.This phase gives probably the first example of lithium distribution in both A and B sites of A2BO4-type mixed oxides. The high coao ratio suggests a strong elongation of FeO6 octahedra induced by a high spin Fe(IV) d4 configuration. The results of structural studies and of Mössbauer analysis, confirming the above conclusions, are reported.  相似文献   

7.
Single crystals of tricalciumborate were grown by the flux method. Ca3B2O6 crystallizes in the rhombohedral system with the unit cell parameters aR = 6.3577(7) A?, αR = 85.68(8)°, Z = 2. The equivalent hexagonal lattice parameters are aH = 8.640(1), CH = 11.854(1) A?. The anisotropic thermal expansion parameters αa = (1.00 ± 0.14) × 10?5, αc = (3.60 ± 0.47) × 10?5 were determined by X-ray methods in the temperature interval 25 – 1000°C.  相似文献   

8.
Twins of Mn1?xGa2+23xS4 were used for crystal structure determination. Twinning is explained by a reticular pseudomerihedry. Axis, plane and obliquity of the twin have been determined. Cell dimensions are: a = b = 5.456(2) A?; c = 10.220(4) A?; α = β = γ = 90°; space group 14; Z = 2. The final R value is 0.059. The material is isostructural with CdGa2S4.  相似文献   

9.
Single crystals of semiconducting compound In2Te5 were grown by chemical transport employing iodine as a transport agent. The crystals had a plate-like habit with the [100] direction perpendicular to the flat surface of the platelets. Nominal dimensions are 10 × 1 × 0.05 mm. In2Te5 has a monoclinic structure with dimensions of the base centered cell: a = 13.47A?, b = 16.51A?, c = 4.365A?, β = 92°5′. The space group is C2c. Pycnometric density is 5.96 g/cm3. The single crystals were all p-type. The conductivity, thermoelectric power and hardness were about 10?5Ω?1cm?1, 650 mkV/°C, and 30 kg/mm2, respectively. The minimum energy gap is 1.26 eV.  相似文献   

10.
Three polymorphic forms of SrNb2O6 are recognized. The monoclinic form has been prepared and studied by x-ray powder diffraction techniques and differential thermal analysis. The results of this study show that SrNb2O6 crystallizes in a pseudo-orthorhombic unit cell with ao = 10.99A?, bo = 7.70A? and co = 5.66A?. Its crystal chemical relations to the other meta-niobates and its thermodynamic stability are discussed.  相似文献   

11.
The new ternary chalcogenides TlxTi6Se8 (x= 0.76) and TlxNb6Se8 (x= 0.70) crystallize with a partially filled up Nb3Te4-structure: space group P63m, z= 1 with
a= 9.882(1) c= 3.590(1)A? (Tl0.76Ti6Se8)
a= 10.033(2) c= 3.475(1)A? (Tl0.70TNb6Se8)
The crystal structures were determined from single crystal diffractometer data and refined to a conventional R-value of 0.077 and 0.055 respectively. The T1 atoms in the octahedral channels cannot be localized. In TlxTi6Se8 diffuse scattering indicates one-dimensional short range order. A model of the cation distribution in Tl0.76Ti6Se8 is discussed.  相似文献   

12.
In copper doped Y2BaZnO5 oxides, copper exhibits a distorted square pyramidal coordination which is consistant with the values of g and A tensors obtained from O band ERS spectrum for a sample containing about 1 % Cu. Three values for g and A are observed, g1 = 2.0495, g2 = 2.0515, g3 = 2.275, ¦A1¦ = 13 10?4cm?1, ¦A2¦ = 10 10?4cm?1 and ¦A3¦ = 147.5 10?4cm?1. Since g1 ? g2 an approximate C4v point symmetry can be assumed for copper. The electronic spectrum shows three bands at 11700, 14500 and 20500 cm?1 which can be assigned to the transitions A1 → B1, B2 → B1 and E → B1 respectively. The orbital reduction parameters are calculated and the bonding covalency is discussed.  相似文献   

13.
A probable model for the structure of the orthorhombic A - type neodymium hydroxycarbonate is presented. It relies on an optical determination of the site symmetry of OH?, CO2?3, and Nd3+ atoms from infrared and visible absorption spectra, together with a computation of 50 X-ray diffraction lines intensities of a high resolution Guinier orthorhombic powder pattern (a = 4,953 A?, b = 8,477 A?, c = 7,210 A?; space group Pmcn (no62)). The CO2?3 groups lies flat between mettalic planes as in the aragonite type of structure and are linked to OH? by hydrogen bond (d(CO2?3 ? OH?) = 2,52 A?). The rare earth coordination is nine fold: two OH? groups being closer (2,58 Å) than the seven oxygen from the CO2?3 groups (2,58 to 2,70 Å).  相似文献   

14.
Pyrochlore type rare-earth vanadites (Ln2V2O7) were prepared and some physical properties were investigated. Ln2V2O7 (Ln:Tm, Yb or Lu) crystallized in the cubic space group Oh = Fd3m, a0 = 9.9575A?, 9.9346A?and 9.9231A? for Tm2V2O7, Yb2V2O7 and Lu2V2O7, respectively. These compounds were all n-type semiconductors and paramagnets in the temperature range 90–300K.  相似文献   

15.
(CH3NH3)2CdBr4 and Cs2CdBr4 are two compounds with a tetrahedral CdBr4-coordination. Their room temperature structures are determined. (CH3NH3)2CdBr4: monoclinic, P21c, a = 8.1227(13) A?, b = 13.4355(16) A?, c = 11.4194(13) A?, β = 96.194(11) °, z = 4. Cs2CdBr4: orthorhombic, Pnma, a = 10.235(5) A?, b = 7.946(3) A?, c = 13.977(5) A?, z = 4.  相似文献   

16.
The creep and fracture properties of 12Cr12Mo14V ferritic steel have been determined over the stress range 125 to 362 MNm?2 at 838 K using high precision, constant stress equipment. When the variation of the rupture life, tf, and the secondary creep rate, ?dots, with stress, σ, was described as fα?dotsασn a stress exponent of was recorded. Comparison with long term data then established that, at stresses below ~ 100 MNn?2, n decreased gradually until values close to unity were obtained at stresses approaching those encountered in electricity generating plant. This decrease in stress exponent is shown to be attributable to a progressive loss of creep resistance associated with changes in carbide dispersion rather than to any change in the mechanisms by which deformation and failure occur.  相似文献   

17.
A new compound with composition Cu0.75 VS2 has been prepared. Its preparation, X-Ray structure, electrical and magnetic properties are reported. The structure is related to the CdI2-type, as in the case of the previously described CuxTiS2 (1); in Cu0.75 VS2, Cu atoms are ordered in tetrahedral sites between the CdI2-type subunits, whereas in CuxTiS2 Cu atoms are disordered in two independent sites. The vanadium atoms are shifted with respect to the titanium sites which leads a monoclinic distortion of the hexagonal cell. The relation between the CdI2 unit cell and the true monoclinic cell of Cu0.75 VS2 is:
amono = 2ahex3 ; bmono = 43a2hex + c2hex9 ; cmono = 2ahex
In Cu0.75 VS2, vanadium atoms occupy two independent sites, three vanadium atoms forming a triangular cluster (V2—V3 distances are 2.91 Å and V3—V3 are 2.92 Å) while one vanadium atom is isolated (V1?V2 = 3.36 A? and V1?V3 = 3.37 A?. The physical properties exhibit a transition at 50°K approximately, the magnetic susceptibility being temperature-independent above and temperature dependent below the transition (Curie-Weiss behavior). Resistivity and Hall measurements confirm the metallic nature of the compound and show the existence of the low temperature transition. The observed properties could be interpreted as a result of the low temperature localisation of the 3d electron of V1.  相似文献   

18.
Three new compounds, X3InO6 (X = Gd, Tb, Lu) were prepared at 1–4 GPa, ~1050°C. They are monoclinic, space group P21n with a ? 8.9A?, b ? 9.8 A?, c ? 5.9A?, β ~ 95° and Z = 4.  相似文献   

19.
n-PbTep+?Pb1?xSnxTe heterojunctions with a long wavelength spectral cutoff (λc ≈ 6 μm) were prepared using the double-channel hot wall technique. The electrical and photoelectrical properties of the heterojunctions at 77, 197 and 300 K were investigated. Detectors with RoA equal to 170 Ω cm2 and a quantum efficiency of 25–40% were obtained. Reasons for the shift of the long wavelength spectral cutoff of the heterojunctions towards shorter wavelengths are given.  相似文献   

20.
The non stoichiometric compound V0.78PS3 has been obtained as single crystals from a preparation corresponding to the atomic ratio V/P/S = 1/1/3. It cristallizes with monoclinic symmetry, space group C2/m, with the unit cell parameters a = 5.867(1) A?, b = 10.160(2) A?, c = 6.657(1) A?, β = 107.08(2)°, V = 379.3(1) A?3 and Z =4. The structure refinement was made down to a reliability factor value R = 3.3% from 445 reflexions (I > 3 σ (I)) and 31 variables. The material has same layer structure as FePS3 with the occurrence of the thiophosphate anion (P2S6)4?-including a P2 pair. In V0.78PS3, the charge equilibrium implies the following developped formula : V0.34II V0.44III0.22 PIV S3?II. The phase is a semi-conductor with a small activation energy of 0.24 eV, in accord with a vanadium mixed valence, and it presents, at low temperature, an antiferromagnetic order (TN = 62 K).  相似文献   

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