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1.
Single-crystal studies on BeP2 indicate that this compound possesses an OD structure. The substructure has a tetragonal unit cell with: a = 3.546 Å, c = 15.01 Å, Z = 4, space group: . The final R factor has a value of 0.033. The atom sites in this substructure correspond to the sites of diamond if the latter is described with a tetragonal cell, where and c = 3adiamond. A short-range order governs the occupation of these sites with Be and P atoms. Each Be has four tetrahedral P neighbors and every P has two Be and two P neighbors. Consideration of the maxima on the diffuse streaks between the sharp reflections of the substructure leads to an intermediate unit cell with a = 7.09 Å and c = 30.02 Å. Coordination considerations allow a structure proposal to be formulated for this intermediate structure which is triclinic but pseudotetragonal. The true unit cell is also pseudotetragonal with a = 7.09 Å and c = N · 15.01 Å, where N is a large integer. 相似文献
2.
The compound Th0.25 NbO3 melts congruently at 1390°C. Single crystals obtained by slow cooling from the melt are transparent and show uniaxial optical properties. A single-crystal X-ray analysis confirms the tetragonal cell found by Kovba and Trunov from a powder data and gives a = 3.90 Å and c = 7.85 Å. No systematic absence of the hkl reflections is observed on precession films. The relative intensities of the main reflections are characteristic of a perovskite-like arrangement ABO3 whose large dodecahedral A sites are only partly occupied. Several domains have been found in the perovskite-type solid solution (1 ? x) Th0.25NbO3-x NaNbO3. For 0 ? x ? 0.5 the phases have a tetragonal cell with and as in pure Th0.25 NbO3. When 0.6 ? x ? 0.8 the corresponding phases crystallize with a small cubic cell (Å), while phases with 0.9 ? x ? 1 have an orthorhombic cell (). 相似文献
3.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Daniel Fruchart 《The Journal of chemical thermodynamics》1983,15(12):1169-1180
The heat capacity of the solid solution Mn3.2Ga0.8N was measured between 5 to 330 K by adiabatic calorimetry. A sharp anomaly with first-order character was detected at TA = (160.5±0.5) K, corresponding to a magnetic rearrangement and a lattice expansion. No sharp anomaly was observed at Tc ≈ 260 K where the magnetic ordering takes place; instead, a smooth shoulder was detected. The thermodynamic functions at 298.15 K are , , , . At low temperatures the coefficient for the linear electronic contribution to the heat capacity was derived: γ = (0.031±0.003) J·K?2·mol?1. Moreover, the different contributions to the heat capacity were obtained and the electronic origin of the phase transitions was established. 相似文献
4.
Junichiro Mizusaki Masafumi Yoshihiro Shigeru Yamauchi Kazuo Fueki 《Journal of solid state chemistry》1985,58(2):257-266
In order to elucidate the defect structure of the perovskite-type oxide solid solution La1?xSrxFeO3?δ (x = 0.0, 0.1, 0.25, 0.4, and 0.6), the nonstoichiometry, δ, was measured as a function of oxygen partial pressure, PO2, at temperatures up to 1200°C by means of the thermogravimetric method. Below 200°C and in an atmosphere of PO2 ≥ 0.13 atm, δ in La1?xSrxFeO3?δ was found to be close to 0. With decreasing log PO2, δ increased and asymptotically reached . The value corresponding to was about ?10 at 1000°C. With further decrease in log PO2, δ slightly increased. For LaFeO3?δ, the observed δ values were as small as <0.015. It was found that the relation between δ and log PO2 is interpreted on the basis of the defect equilibrium among Sr′La (or V?La for the case of LaFeO3?δ), V··O, Fe′Fe, and Fe·Fe. Calculations were made for the equilibrium constants Kox of the reaction and Ki for the reaction Using these constants, the defect concentrations were calculated as functions of PO2, temperature, and composition x. The present results are discussed with respect to previously reported results of conductivity measurements. 相似文献
5.
Evidence is presented for normal-spinel domain of homogeneity between the compositions InS1.50?ε and InS1.35. Structural study of a single crystal of composition InS1.44 indicates indium vacancies on the tetrahedral sites. The compound In2S3, regardless of conditions of formation, is a tetragonal superstructure of the spinel lattice (a0) with and c = 3a0. The spinel-type domain shows peritectic decomposition at 850°C for the composition InS1.40. 相似文献
6.
The crystal structure of trisodium monophosphate hemihydrate was determined. The space group is and a unit cell contains eight formula units. The unit cell dimensions of are a = 9.631(3), b = 5.416(2), c = 16.938(8) Å, β = 102.60(5)°. The final R value is 0.027 for a set of 1430 independent reflections. This atomic arrangement is mainly a three-dimensional network of distorted NaO6 octahedra. The hydrogen bonding scheme is given. 相似文献
7.
John R. Günter 《Journal of solid state chemistry》1980,35(1):43-49
Thermal dehydration of copper(II) formate tetrahydrate leads to a modification of the anhydrous salt different from that produced by direct preparation of the latter. As the dehydration is a topotactic process, the known crystal structure of the tetrahydrate and the topotactic orientation relations can be used to deduce the crystal structure of the product. Single-crystal X-ray diffraction patterns of decomposed pseudomorphs yield the following unit cell for the dehydrated formate: monoclinic, a = 8.195 ? 0.006 Å, b = 7.925 ? 0.006 Å, c = 3.620 ? 0.005Å, β = 122.21 ? 0.09°, probable space group . The structure contains copper formate layers very similar to those in the tetrahydrate, stacked in such a way that columns of distorted coordination polyhedra, linked by formate bridges, are formed. The topotactic dehydration occurs in such a way that two-dimensional elements of the structure are unaltered but the mode of stacking is changed. 相似文献
8.
Jean-Claude Jumas Etienne Philippot Françoise Vermot-Gaud-Daniel M. Ribes Maurice Maurin 《Journal of solid state chemistry》1975,14(4):319-327
The crystal structure of Na4SnS4 and Ba2SnS4 (α) were determined.Na4SnS4 crystallizes in tetragonal system, space group with parameters a = 7.837 Å, c = 6.950 Å, Z = 2 and Ba2SnS4 (α) in the monoclinic system, space group with a = 8.481 Å, b = 8.526 Å, c = 12.280 Å, β = 112.97° and Z = 4.In these compounds, the crystal structure is built up from discrete orthothiostannate tetrahedra SnS4. The structure of Ba2SnS4 (α) is modified K2SO4β type. 相似文献
9.
Iwami Higashi 《Journal of solid state chemistry》1983,47(3):333-349
The crystal structure of γ-AlB12 (P212121; a = 16.573(4), b = 17.510(3), c = 10.144(1)Å) was reinvestigated by single-crystal X-ray diffractometry and the nature of the metal distribution in the boron framework examined. Starting from the structure data published by Hughes et al. (Journal of the American Chemical Society 83, 2337 (1977)), 458 independent parameters, including the occupancies of 11 Al sites, were finally refined to a conventional R value of 2.9%. A total of 5282 observed unique reflections (MoKα radiation; 2θ < 64°) were used. Although distributed in an apparently complicated manner, the aluminum atoms occur in the boron framework according to a simple rule as in the crystals of the α-AlB12 structure type. The numbers of the valence electrons of Al, allotted to the six boron subunits, B12(i–iv), B20-(C2, Cs), proportionately to the contact frequencies of Al with the units, are 2.2, 1.9, 2.2, 1.9, 5.3, and 5.2, respectively. The charge assignment is compatible with the ionic formula , proposed from preliminary molecular orbital calculations. A negative charge balance among the six boron units at about 1:1:1:1:3:3 seems to be essential for making up the stable boron framework of γ-AlB12. 相似文献
10.
K.R. Poeppelmeier M.E. Leonowicz J.C. Scanlon J.M. Longo W.B. Yelon 《Journal of solid state chemistry》1982,45(1):71-79
Low-temperature synthesis of the oxygen-deficient compound CaMnO2.5 from polycrystalline CaMnO3 preserves the existing structural framework of the oxidized precursor. The crystal structure of CaMnO2.5 was determined using neutron powder diffraction data analyzed by the Reitveld profile refinement method. The structure of the reduced phase can be described by the orthorhombic distortion , where ac is the simple cubic distance (~3.7 Å) characteristic of the Mn4+O2?Mn4+ framework in CaMnO3. The unique features of the structure are five-coordinate Mn3+ cations with nearly square pyramidal (~C4v) coordination and ordered oxygen vacancies. The preparation, structure refinement, and noncubic distortions of single crystals of CaMnO3 are also described. Attempts to transform single crystals of CaMnO3 into CaMnO2.5 by well-ordered topotactic changes have not been successful. 相似文献
11.
Sulfur hexafluoride has a body-centered cubic phase (a = 5.915(3) Å) between its melting point (222.4°K) and 93°K, below which a lower symmetry phase exists. NMR studies show that in both phases there is rapid reorientation of the sulfur hexafluoride molecules. From a neutron diffraction pattern collected at 193°K with λ = 1.086 Å, the data were not satisfied by a model with a spherically symmetrical fluorine density nor by a refinement with conventional ellipsoidal-shaped atoms. The latter gave systematically low S-F distances and abnormally high βij thermal factors. Good agreement was obtained by a combination of Kubic Harmonics with full-matrix least-squares analysis of the neutron profile pattern. The refinement was made with one variable Kubic Harmonic coefficient a2 = 5.94(11), with and . Only four least-squares variables were required with 225 observations in the range of one or more hkl reflections to 2θ = 58.3°. AS-F distance of 1.542(4) Å, obtained from the neutron diffraction data, is in good agreement with the reported value of 1.564(10) Å found from electron diffraction measurements of the vapor. The disordered fluorine distribution has broad maxima on the cell edges similar to those found in the plastic cubic phases of MoF6 and WF6. 相似文献
12.
Z. Dobkowski 《European Polymer Journal》1984,20(4):399-403
Linear and branched bisphenol A polycarbonate (PC) samples were characterized by their average molecular weights, and , polydispersity degree , and branching degree gv. The weight fraction of microgel was also determined for branched samples. The samples were amorphized and densities were measured at 23°C to obtain the values of specific volume, vsp. The dependence of vsp on molecular characteristics is described by the multivariable power function , where Δvsp = vsp ? vsp,∞, and Asp, a, apx and ab are constants. It has been confirmed that a = ?1, apn = 0 and apw = 1. It has also been found that the branching exponent ab significantly depends on microgel content. The relationships found for PC should, in principle, be valid for other polymers. Examples based on literature data are given for linear polyethylene and polydimethylsiloxane. 相似文献
13.
Z. Dobkowski 《European Polymer Journal》1984,20(3):265-267
A method for evaluation of the type of average, which is experimentally obtained for a given property of polydisperse polymer, is described. A multivariable power function where P is the polymer property, is the x-average molecular weight, q is the polydispersity degree, Ap, a and apx are constants, and the apx = 0 criterion (apx being the polydispersity exponent) is used for this purpose. 相似文献
14.
A new hydrate of tungsten trioxide, has been obtained by hydrothermal treatment at 120°C of an aqueous suspension of either tungstic acid gel or crystallized dihydrate. This hydrate has been characterized by different methods. A crystallographic study was carried out from X-ray powder diffraction. The hydrate crystallizes in the orthorhombic system: a = 7.359(3) Å, b = 12.513(6) Å, c = 7.704(5) Å, Z = 12. The existence of structural relationships between the hydrate, , and the product of dehydration, hexagonal WO3, has permitted us to propose a structural model in agreement with the experimental data. must be regarded as an interesting compound because its dehydration leads to a new anhydrous tungsten trioxide, hexagonal WO3. 相似文献
15.
Crystal structures for the fluorite-related phases CaHf4O9) and Ca6Hf19O44 () have been determined from X-ray powder diffraction data. qf1 is monoclinic, , with a = 17.698 Å, b = 14.500Å, c = 12.021 Å, β = 119.47° and Z = 16. qf2 is rhombohedral, , with a = 12.058 Å, α = 98.31° and Z = 2.Both phases are superstructures derived from the defect fluorite structure by ordering of the cations and of the anion vacancies. The ordering is such that the calcium ions are always 8-coordinated by oxygen ions, while the hafnium ions may be 6-, 7-, or 8-coordinated. The closest approach of anion vacancies is a fluorite subcell vector, and in each structure vacancies with this separation form strings. 相似文献
16.
S.C. Abrahams R.C. Sherwood J.L. Bernstein K. Nassau 《Journal of solid state chemistry》1973,8(3):274-279
Three anhydrous polymorphs of cupric iodate, two hydrates, and the basic iodate salesite have been investigated. α-Cu(IO3)2 is monoclinic, space group P21, with a = 5.551 ± 0.008, b = 5.101 ± 0.004, c = 9.226 ± 0.010 Å and β = 95°4′ ± 11′, with two formulas in the unit cell. Below ΘN = 8.5 K, α-Cu(IO3)2 is antiferromagnetic and also pyroelectric. β-Cu(IO3)2 is triclinic, space group , with a = 11.230 ± 0.006, b = 11.368 ± 0.009, c = 10.630 ± 0.009 Å, α = 99°18.3′ ± 0.3′, β = 107°0.4′ ± 0.2′ and γ = 114°23.8′ ± 0.2′ and eight formulas per unit cell: the crystal is paramagnetic to 1.4K. γ-Cu(IO3)2 is monoclinic, space group , with a = 4.977 ± 0.004, b = 6.350 ± 0.004, c = 8.160 ± 0.004 Å and β = 92°20′ ± 4′, with two formulas per unit cell; γ-Cu(IO3)2 becomes antiferromagnetic below ΘN = 5 K. Cu(IO3)2·2H2O is monoclinic, space group , with a = 6.725 ± 0.005, b = 4.770 ± 0.007, c = 11.131 ± 0.013 Å and β = 103°1′ ± 4′, with two formulas per unit cell; Cu(IO3)2·2H2O is paramagnetic to 1.4 K. (mineral bellingerite) is triclinic, space group , with a = 7.197 ± 0.005, b = 7.824 ± 0.004, c = 7.904 ± 0.004 Å, α = 105°2′ ± 2′, β = 97°7′ ± 2′ and γ = 92°54′ ± 2′ with three formulas per unit cell; this crystal is paramagnetic to 1.4 K, with a moderate antiferromagnetic Cu-Cu interaction. Cu(OH)IO3 (mineral salesite) is orthorhombic, with a = 10.772 ± 0.004, b = 6.702 ± 0.002 and c = 4.769 ± 0.002 Å and four formulas per unit cell. The magnetic susceptibility indicates the possibility of antiferromagnetic ordering at 162 K; strong antiferromagnetic interactions give Θp = ?340 K. The only copper iodate studied that generates second harmonics is α-Cu(IO3)2. Indexed powder patterns are given for all six compounds. 相似文献
17.
The incongruent vaporization reactions of Ta2S and Ta6S have been investigated by mass-loss effusion in the temperature range 1576 to 1902 K. By extrapolation of PS(obs) to equilibrium the enthalpies of the reactions and Ta6S = 6 Ta(s) + S(g) were found to be and , respectively. Comparison between the above values, determined by a 2nd law treatment, and 3rd law values was used to derive fef (“free energy function”) values for Ta and S in the compounds. These postulated fef's, which apply only to the elements as present in the compounds measured, are compared to tabulated quantities for the pure solid elements to provide a criterion for 2nd and 3rd law evaluation. 相似文献
18.
Michael I. Bruce Trevor W. Hambley Michael R. Snow A.Geoffrey Swincer 《Journal of organometallic chemistry》1984,273(3):361-376
Reactions between MX(PPh3)2(η-C5H5) (M = Ru, X = Cl; M = Os, X = Br) and 2-CH2CHC6H4PPh2 afford Ph2)(η-C5H5); the Os complex is obtained in two isomeric forms. The X-ray structure of the major isomer shows the CC double bond (OsC, 2.214, 2.195 Å; CC, 1.57 Å) is almost coplanar with the OsBr vector, with the terminal C cis to Br; the minor isomer is assumed to have the alternative, more sterically congested conformation, with the β-C cis to Br. The chlororuthenium complex reacts with NaOMe/MeOH to give the corresponding hydrido complex, which also exists as two isomers in solution; reaction of this complex with CS2 gives the expected dithio acid derivative Ph2)(η-C5H5), together with small amounts of a complex assumed to be Ph2](η-C5H5). The X-ray structure of the major product reveals an unusual η3-S2C mode of coordination of the dithio acid fragment (RuS, 2.418, 2.426(1) Å; RuC 2.175(4) Å). Crystals of OsBr(η2-CH2CHC6H4P)Ph2)( η-C5H5) are monoclinic, space group P21/n, with a 12.696(2), b 21.719(6), c 15.929(3) Å, β 79.77(2)°, Z = 8; 2867 data (I > 2.5σ(I)) were refined to R = 0.040, Rw = 0.044. Crystals of Ph2)(η-C5H5) are orthorhombic, space group Pbca, with a 8.921(2), b 15.982(9), c 32.216(5) Å, Z = 8; 1685 data (I > 2.5σ(I)) were refined to R = 0.027, Rw = 0.030. 相似文献
19.
Single crystals of the title compounds have been grown by the Czochralski technique. Pb4P2O9 crystallizes in the space group with the parameters a = 9.4812 Å, b = 7.1303 Å, c = 14.390 Å, β = 104.51° and Pb8P2O13 in with a = 10.641 Å, b = 10.206Å c = 14.342 Å, β = 98.34°. 相似文献