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1.
The luminescence associated with the Eu3+ ion in LiEuCl4 has been studied at cryogenic temperatures under conditions of high resolution. Emission was observed to originate from both the 5D0 and 5D1 excited states, and transitions to the , and 7F4 ground levels were observed. The fine structure observed within these emission bands was found to be consistent with the existence of an effective D4 site symmetry for the emitting Eu3+ species, even though the europium polyhedron was found to be that of a bisdisphenoid. 相似文献
2.
Use of Nd3+, Eu3+, and Gd3+ as local structural probes allows the determination of the rare earth positions in the NaxSr3?2xLnx(PO4)2 (Ln = La to Tb) and KCaLn(PO4)2 phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation and levels of the Gd3+ ions. 相似文献
3.
E.M. Akulonok V.Ya. Khaimov-Malkov Yu.K. Danileiko A.A. Manenkov V.S. Nechitailo T.P. Lebedeva 《Journal of solid state chemistry》1978,26(1):17-25
A problem of trap diffusion, that is diffusion of point defects in crystals participating in a solid-phase chemical reaction with motionless impurity ions, is solved. Time dependences of the reaction-front displacement, Xf, and its steepness, are determined analytically for N0 ? C0 and numerically for all relations of N0 and C0where C0 and N0 are the initial concentration of impurity and the eqilibrium defect concentration, respectively, D is a diffusion coefficient, and g is a chemical reaction constant. Dependence of Xf vs C0 and t is confirmed for oxygen annealing of corundum crystals doped with titanium which, reacting with the point defects, changes its valency. The data are obtained for dependence of displacement Xf upon partial oxygen pressure and thermotreatment temperature as well as upon the sign of the constant electric field applied to the sample. From these data we conclude that the reaction of titanium impurity, changing from the three-valent to the tetravalent state at the activation energy of 80 ± 8.5 kcal/mole is due to anisotropic diffusion of charged aluminum vacancy and holes in the valence band. The diffusion coefficient for that process at 1500°C is estimated to be larger than 10?5 cm2/sec. Using the trap-diffusion features, the concentration of optical centers of the 0.315-μm absorption band in ruby is also estimated. 相似文献
4.
Paul Poix 《Journal of solid state chemistry》1981,40(2):175-179
The study of K2NiF4 and perovskite structure type by the “method of invariants” leads to the relationship: , where (A-X)9 and (A-X)12 are the invariant values associated with cation A in coordination number 9 and 12. In the case where A = K+ and X = F?, we propose the relationship: where R is the coordination number. 相似文献
5.
Proton NMR relaxation times (T2T1, and T1?) and absorption spectra are reported for the compounds H1.71MoO3 (red monoclinic) and H0.36MoO3 (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH2 groups coordinated to Mo atoms in H1.71MoO3 and as pairs of OH groups in H0.36MoO3. The room temperature lineshape for H1.71MoO3 shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give EA = 22 kJ mole?1 and for H1.71MoO3 and EA = 11 kJ mole?1 and for H0.36MoO3. 相似文献
6.
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
7.
D.A. Lemenovskii V.P. Fedin A.V. Aleksandrov Yu.L. Slovohotov Yu.T. Struchkov 《Journal of organometallic chemistry》1980,201(1):257-268
Electron-acceptor properties of bis-niobocenes (η5-C5H4Y)(H)b(H)(η5-C5H4Y) with X Y H and XY SiMe2OSiMe2have been investigated. Bis-niobocenes are shown to readily add two electrons forming stable salts of the corresponding dianions [(η5-C5H4Y)(H)Nb(η5 : η1- C5H3X)2Nb(H)(η5-C5H4Y)]2-. The surplus electrons can be removed to give quantitative regeneration of initial neutral bis-niobocenes. The crystal and molecular structure of the title compound has been determined; R 0.044, interatomic distance are Nb…Nb 3.93, NbH 1.62, average NbC(π) 2.36, NbC(σ) 2.31 Å, other distances correspond to the usually observed values. Unlike the neutral bis-niobocenes, there is no direct metalmetal bond in the dianionic structures. This conclusion is supported by electronic spectra of neutral and dianionic species. 相似文献
8.
The addition of trimethylphosphane to five-membered metallacyclic vinylketone complexes of the type ArR) (I) (Ar = η5-aromatic ring system: C5H5, C5H4Me, C5Me5; R = Me, Et, n-Bu; M = Mo, W) in pentane solution results in the formation of the ylidic metallacyclopropane complexes ArH(COR)] (II). In these 1:1 adducts the three-membered ring is stabilized by an electron-donating phosphonium and an electron-attracting acyl substituent. The negative charge in the ylidic complexes II is localized on the central metal providing it with Lewis base properties. An extraordinary high electron density can be observed on the metal of the derivative C5H5H-(COMe)] (III) which is formed by a 1:2 addition of C5H5W(CO)(C2H2)-(COMe) and PMe3. The metallacyclopropane complexes II and III are characterized by IR, 1H NMR, 13C NMR, 31P NMR and mass spectroscopy. For C5H5H(COMe)], the results of an X-ray structure determination are presented. 相似文献
9.
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
10.
D.J. Ruben S.G. Kukolich L.A. Hackel D.G. Youmans S. Ezekiel 《Chemical physics letters》1973,22(2):326-330
Very high resolution measurements of hyperfine structure on the P(13) and R(15), 43?0, transitions in iodine 127 were made using laser molecular beam spectroscopy. The observed linewidth was 300 kHz (fwhm) giving a resolution of 5 × 10?10 The observed spectrum was fitted to obtain a quadrupole coupling strength difference of ΔeQq = 1906 ± 2 MHz and a spin rotation interaction strength difference of ΔCI = 181 ± 7 kHz between the upper and lower levels of the P(13) transition. For the R (15) transition ΔeQq = 1905 ± 2 MHz and ΔCI = 167 ± 5 kHz. 相似文献
11.
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
12.
The novel λ4-thia-λ5-phospha-h2-manganabicyclo[2.2.1]heptadienes (OC)3Mn[] (R1 = CH3, C6H5; R2 = CO2CH3, CO2C2H5, CO2C6H11) are formed by action of the activated alkynes R2C CR2 on the heterocycles [(OC)4MnPR12S]2 via the isolable, five-membered heterometallacyclopentadienes (OC)4(R2). The compound with R1 = CH3 and R2 = CO2CH3 crystallizes in the triclinic space group P with Z = 2 and separates quantitatively the thiophene derivative under CO pressure or by reaction with (NH4)2Ce(NO3)6. The use of various acetylenes and of acetylenes with different alkyl groups yields the unsymmetric substituted manganabicycloheptadienes (OC)3Mn[] (R2 = CO2CH3, R3 = R4 = CO2C2H5; R2 = R4 = CO2CH3, R3 = H). With propionic acid methylester the alkyne insertion proceeds regiospecifically. With Raney nickel selective S elimination under ring contraction and formation of the λ4-phospha-h2-manganabicyclo[2.1.1]hexenes (OC)3Mn[R12] (R1 = CH3: R2 = R3 = CO2CH3, CO2C2H5; R2 = CO2CH3, R3 = H; R1 = C6H5: R2 = R3 = CO2C2H5) occurs. (OC)3Mn[(CH3)2] (R2 = R3 = CO2CH3) crystallizes in the monoclinic space group P21/m with Z = 2. The IR and NMR spectra of the heterocycles are discussed in detail. 相似文献
13.
J. Mulak 《Journal of solid state chemistry》1977,21(2):117-126
Based on the experimentally determined temperature dependence of the paramagnetic susceptibility of tetragonal USiO4 within the temperature range 2–500°K, the crystal field parameters of D2d symmetry have been estimated (in cm?1): B02 = ?24, B04 = ?1.25, B44 = ?12.8, B06 = ?0.031, B46 = 0.51, and . The Γ5 doublet with the approximate composition: 0.78|±1> + 0.63|?3> is the ground level of the U4+ ion. Singlet Γ1 lying ca. 100 cm?1 above is the first excited level. The total splitting of the 3H4 term of the U4+ ion was estimated to be equal to ca. 7500 cm?1. 相似文献
14.
A preliminary study of the PbF2LnF3 systems (Ln = lanthanides and Y) has allowed the characterisation of three phases: a disordered fluorite-like solid solution Pb1?xLnxF2+x the domain of which increases with increasing temperature and dopant ion radius, and two anion-excess fluorite related superstructures: Pb2YF7 (tetragonal, space group I4 or ) and Pb4Ln3F17 with Ln = SmLu (rhombohedral, space group ). The crystallographic characteristics of the two ordered phases have been confirmed by electron diffraction. 相似文献
15.
The Sr2+1?yLa3+yFeO3 system with 0.1 ≦ y ≦ 0.6 has been studied mainly by the Mössbauer effect. The results are discussed referring to the Ca1?xSrxFeO3 system. The following four kinds of electronic phases have been observed: the paramagnetic and the antiferromagnetic average valence phases and the corresponding mixed valence phases. Two kinds of Fe ions coexist, in general, in the mixed valence phases. In the antiferromagnetic mixed valence phase, typically at 4 K, the magnetic hyperfine field and the center shift each takes a wide range of value depending on the composition, while a beautiful correlation is kept between them. The extreme values are close to those expected for Fe3+ and Fe5+. The appropriate chemical formulas are, therefore, Ca1?xSrxFe(3+Δ)+0.5Fe(5?Δ)+0.5O3 and . 相似文献
16.
The magnetic interaction in the structural units [Fe2O7]8?, built of two corner-sharing FeO4 tetrahedra, in Na8Fe2O7 () has been studied by magnetic susceptibility measurements (4.2–500 K). An exchange integral of ?37 K is obtained by comparison of the experimental values and the calculated ones using a Heisenberg-Dirac-Van Vleck-type Hamiltonian ? = . The hypothesis of magnetically isolated [Fe2O7]8? groups is corroborated by Mössbauer spectroscopy between 1.5 and 77 K. The susceptibility measurements of the solid solutions Na8Fe2?xMxO7 (M = Al, Ga; 0 ≤ x ≤ 0.2 for Al; 0 ≤ x ≤ 2 for Ga) leads to the same conclusion of the existence of isolated Fe3+Fe3+ pairs in Na8Fe2O7. The type of substitution of Fe by Al or Ga is determined; homonuclear Fe3+Fe3+ and M3+M3+ pairs and heteronuclear Fe3+M3+ pairs are formed. 相似文献
17.
Takamasa Ishigaki Shigeru Yamauchi Junichiro Mizusaki Kazuo Fueki Hifumi Tamura 《Journal of solid state chemistry》1984,54(1):100-107
The tracer diffusion coefficient, , of oxide ions in LaCoO3 single crystal was determined over the temperature range of 700–1000°C by a gas-solid isotopic exchange technique using 18O tracer. For the determination, two methods, the gas phase analysis and the depth profile measurement, were employed. Under an oxygen pressure of 34 Torr, the temperature dependence of in LaCoO3 was expressed by at 950°C was found to be proportional to P?0.35O2. The diffusion of oxide ions occurs through a vacancy mechanism. The activation energy for the migration of oxide ion vacancies was estimated as 18 kcal · mole?1. 相似文献
18.
B. Bochu M.N. Deschizeaux J.C. Joubert A. Collomb J. Chenavas M. Marezio 《Journal of solid state chemistry》1979,29(2):291-298
A series of titanates which have perovskite-like arrangements and are isostructural with [CaCu3](Mn4)O12 have been synthesized. The total charge of the A sites can be modified (1) by substituting the Ca2+ cations with monovalent ones and the tetravalent manganese cations of the B sites by a mixture of (Ti4+ + M5+) in which M = Ta, Nb, Sb, or (2) by substituting the Ca2+ cations by a combination of cations plus vacancies. In this case, if the total charge of the A sites is 2, one obtains compounds such as and ; on the contrary, if the charge is less than 2, then one has to compensate it by changing that of the B sites. This leads to compounds such as [□Cu3](Ti2M2)O12 (M = Ta, Nb, Sb). 相似文献
19.
Joaquín García Juan Bartolomé Domingo González Rafael Navarro Willem Jacobus Crama 《The Journal of chemical thermodynamics》1983,15(12):1109-1126
We present the heat capacities measured by adiabatic calorimetry from 6 to 350 K, and by differential scanning calorimetry from 300 to 500 K, of CsCrCl3 and RbCrCl3. A first-order transition at Tc = (171.1±0.1) K was detected for CsCrCl3. The RbCrCl3 showed at Tc = (193.3±0.1) K a transition with thermal hysteresis at temperatures just below the maximum. At T1 = (440±10) K a continuous transition was also detected. Furthermore, at TN ≈ 16 K, and for both compounds, a small bump due to magnetic long-range ordering was observed. The thermodynamic functions at 298.15 K are
CsCrCl3 | 15.38 | 26.49 | 3503.2 | 14.735 |
RbCrCl3 | 15.76 | 25.99 | 3556.8 | 14.384 |