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1.
Raman and infrared spectra of polycrystalline6Li2C2O4 and7Li2C2O4 have been investigated in the wavenumber region from 1,800 to 40 cm–1. The internal C2O4 –2 vibrations have been studied on the basis of a D2h molecular structure and the correlation field splittings have been found to be about 40 cm–1 for the stretching modes and about 15 cm–1 for the bending modes. The external vibrations of the Li+ and C2O4 –2 sites have been discussed by considering the results of the factor group analysis and the6Li/7Li isotope effect on the normal vibrations.
Raman- und Infrarot-Spektren von6Li2C2O4 und7Li2C2O4
Zusammenfassung Es wurdenRaman- und IR-Spektren von polykristallinem6Li2C2O4 und7Li2C2O4 im Bereich der Wellenzahlen von 1800 bis 40 cm–1 untersucht. Die internen Schwingungen wurden auf der Basis einer D2h Molekülstruktur analysiert. Für die Streckschwingungen wurde eine Korrelationsaufspaltung von etwa 40 cm–1 gefunden, für die Deformationsschwingungen etwa 15 cm–1. Die Diskussion der externen Schwingungen von Li+ und C2O4 –2 erfolgte unter Berücksichtigung der Resultate der Faktorgruppenanalyse und des6Li/7Li Isotopeneffekts auf die Normalschwingungen.
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2.
The crystal structures of the lithium-rich and lithium-deficient spinel phases Li2[Mn2]O4 and Li0.2[Mn2]O4 have been determined by neutron-diffraction techniques. Structure refinements confirm earlier reports that the [Mn2]O4 framework of the Li[Mn2]O4 spinel remains intact during both lithium insertion and extraction, but demonstrate unequivocally that in Li2[Mn2]O4 the Li+ ions reside in face-shared tetrahedra and octahedra of the cubic-close-packed oxygen-anion array; in Li0.2[Mn2]O4 the Li+ ions are located randomly on only the tetrahedral sites of the spinel structure.  相似文献   

3.
The formation and mobility of Li point defects in Li(2)B(4)O(7) are investigated theoretically with periodic quantum chemical calculations. Calculated defect formation energies obtained with a density functional theory/Hartree-Fock hybrid method and with the Perdew-Wang density functional method are compared. The basis set effect is investigated by comparison of results obtained with atom-centered basis functions and plane waves. With both methods only a moderate relaxation is observed for the atoms surrounding the Li defect position. The defect-induced change of electronic properties is investigated by calculating the density of states for the stoichiometric and defective supercells. The activation energy for the movement of a Li(+) ion along the (001) direction is calculated. It is observed that Li(+) ion migrates through a one-dimensional channel formed by the five-vertex lithium-oxygen (LiO(5)) polyhedra. The calculated activation energies are in excellent accord with experiment.  相似文献   

4.
5.
Polarized i.r. reflection spectra of single crystals of Li-2,4-pentanedionate (Li-acac) were recorded in the region from 200–600 cm−1. Bands due to vibrations of the lithium ions were identified using the 6Li/7Li isotopic replacement technique. Various LiO distances as well as different degrees of distortion in the four symmetrically unequal LiO4 coordination polyhedra lead to a specific spectroscopic behaviour for each of these polyhedra. It is therefore possible to suggest an assignment of the observed LiO bands to specific LiO4 groups. The results of a rough calculation support this assignment. A correlation between LiO distances and LiO stretching force constants is proposed.  相似文献   

6.
EPR and optical absorption spectra of Cr3+ ions doped in KZnClSO4 x 3H2O single crystals have been studied at room temperature. The EPR spectrum exhibits a group of three fine structure transitions characteristic of Cr3+ ions. From the observed EPR spectra, the spin-Hamiltonian parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in an octahedral symmetry. From the observed band positions, the crystal field parameters have been evaluated.  相似文献   

7.
Yang Y  Pan S  Li H  Han J  Chen Z  Zhao W  Zhou Z 《Inorganic chemistry》2011,50(6):2415-2419
A new noncentrosymmetric polyborate, Li(4)Cs(3)B(7)-O(14), has been synthesized using the conventional solid state reaction method. It crystallizes in the trigonal space group P3(1)21 (No. 152) with unit cell parameters of a = 6.9313(6) ?, c = 26.799(3) ?, and Z = 3. The new structure contains an infinite three-dimensional matrix that is built from B(7)O(14) building blocks rarely found in anhydrous borate compounds and LiO(n) (n = 4, 5), CsO(n) (n = 9, 10) polyhedra. The optical characterization of the compound indicates that the compound is phase matchable, and the UV cutoff edge is below 190 nm. IR spectroscopy, thermal analysis, and second-harmonic generation were also performed on the reported material.  相似文献   

8.
采用等温蒸发平衡法研究了四元体系K2B4O7-Na2B4O7-Li2B4O7-H2O15℃时的介稳相平衡及平衡液相的物化性质(密度,粘度,电导率,折光率,pH)。根据实验数据绘制了相图,相图中有一个共饱点E,三条单变度曲线E3F,E2F,E1F;三个平衡固相分别为:K2B4O7•4H2O,Na2B4O7•10H2O和Li2B2O4•16H2O;硼酸钾具有最大溶解度,硼酸钠具有最小溶解度。同时,根据试验数据绘制了组成-物化性质关系图,从图可见溶液的密度,粘度和折光率均随着溶液浓度的增大而逐渐增大,在共饱和点F处达到最大值,而溶液的pH值和电导率却随着溶液浓度的增大呈总体下降的趋势。  相似文献   

9.
The room temperature polarized Raman spectra of single crystal Li2SeO4 are assigned using a factor group analysis. The internal optic modes of the selenate ion are responsible for Raman bands from 920 to 440 cm−1, the translational optic modes of the lithium occur in the interval from 444 to 290 cm−1 and the external optic modes of the selenate ion are found between 210 and 70 cm−1. The symmetry-based assignments of these bands are discussed.  相似文献   

10.
K2Al2B2O7 (KABO) is a new nonlinear optical crystal capable of laser harmonic generation in the UV range. However, abnormal UV absorption prevents its application in effectively generating UV light with wavelength shorter than 300 nm. The transmittance spectra of the grown crystals show distinct absorption bands at 216 nm and 264 nm. It is observed that the UV absorption is strongly correlated with iron impurity at a parts per million (ppm) level. Furthermore, electron paramagnetic resonance (EPR) spectra of the absorbing crystals show a strong signal at g = 2.00 position corresponding to a Fe3+ center. A new crystal growth method which reduces the iron content has been proposed and results show that the new KABO crystal is free from the Fe3+ UV absorptions.  相似文献   

11.
Single crystal and powder EPR studies of VO2+ doped di-ammonium hydrogen citrate [(NH4)2C6H6O7] are carried out at room temperature. The angular variation of the EPR spectra show three different VO2+ complexes that are located in different chemical environment, and each environment contains two magnetically inequivalent VO2+ sites in distinct orientations occupying substitutional positions in the lattice. Crystalline field around the VO2+ ion is nearly axial. The optical absorption spectrum shows two bands centred at 16,949 and 12,345cm(-1). Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.  相似文献   

12.
The mechanisms behind the nonlinear optical (NLO) properties of Li2B4O7 are characterized by 7Li static nuclear magnetic resonance (NMR) and magic-angle spinning (MAS) NMR. Furthermore, the structural nature of 3-coordinate BO3 and 4-coordinate BO4 groups is also characterized by the same method. For 7Li and 11B, the spin-lattice relaxation time T1 in laboratory frame gradually decreases with increasing temperature, whereas the spin-lattice relaxation time T in rotating frame, which differs from T1, is nearly constant. In addition, the activation energies of 7Li and 11B, which are obtained via the values of T1 and T, are also compared.  相似文献   

13.
ESR and optical absorption studies of manganese doped ammonium selenate single crystals are performed at X-band and room temperature to ascertain the site symmetry and location of impurity ions in the lattice. Manganese ions are expected to enter the lattice interstitially. Various spin Hamiltonian parameters are determined. Optical absorption study is also done and associated distortion in the crystal lattice is estimated.  相似文献   

14.
EPR study of Mn2+ doped ammonium tartrate single crystals is carried out at room temperature. The spin Hamiltonian parameters are: gx=1.9225+/-0.0002, gy=1.9554+/-0.0002, gz=2.1258+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(191+/-2) x 10(-4) cm(-1), E=(61+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site I and gx=1.9235+/-0.0002, gy=1.9574+/-0.0002, gz=2.0664+/-0.0002, A=(78+/-2) x 10(-4) cm(-1), B=(75+/-2) x 10(-4) cm(-1), D=(180+/-2) x 10(-4) cm(-1), E=(57+/-2) x 10(-4) cm(-1) and a=(22+/-1) x 10(-4) cm(-1) for site II, respectively. The observed optical bands are fitted with inter-electronic repulsion parameters (B and C), crystal field parameter (Dq) and Trees correction (alpha) and the values found are B=752, C=2438, Dq=765 and alpha=76 cm(-1). The data obtained are further used to discuss the surrounding crystal field and the nature of metal-ligand bonding in the crystal.  相似文献   

15.
Electron paramagnetic resonance of VO(2+) doped sodium hydrogen oxalate monohydrate (NaHC(2)O(4).H(2)O) single crystals and powders are examined at room temperature. Single crystal rotations in each of the three mutually orthogonal crystalline planes namely ac*, b*c* and ab* indicate four different VO(2+) complexes with intensity ratios of 4:2:1:1. It is found from the EPR analysis that the Na(+) ions are replaced with the substitutional magnetically inequivalent VO(2+) ions. The powder spectrum also clearly indicates four different VO(2+) complexes, confirming the single crystal analysis. Crystalline field around the VO(2+) ion is nearly axial. The optical absorption spectrum show two bands centered at 15408 and 12453 cm(-1). Spin Hamiltonian parameters and molecular orbital coefficients are calculated from the EPR and optical data, and results are discussed.  相似文献   

16.
Polycrystal Li2B4O7 (LBO) doped with Cu and In was prepared and then sintered at different temperatures. X-ray diffraction (XRD) was applied to get the parameters of the LBO structure, thermoluminescence (TL) and optically stimulated luminescence (OSL) were measured, and a second-order exponential decay model was fitted to the OSL decay curves. The results indicate that the original number of OSL traps that have captured electroncs is linearly related with the sum of TL decay during the OSL process. Mean decay constant of OSL is related to the sintered temperature. The possible reason is that the sintered temperature affects the crystal sizes of the polycrystal, and consequently affects the stimulating lights’s intensity and the photoionization cross-section of the electrons, which have been captured by the traps. __________ Translated from Acta Scientiarum Naturalium Universitatis Sunyatseni, 2005, 44(4) (in Chinese)  相似文献   

17.
On of the hydrogen bonds formed by water molecules in lithium selenate monohydrate is evidently stronger than in the corresponding sulfate, whereas the other one is weaker. The temperature dependence of the stretching and bending modes of water is similar in both compounds, their frequencies decreasing on lowering the temperature. The study of mixed sulfate—selenate compounds made it possible to clearly show that the effective symmetry of the tetrahedral ions is higher than their local crystallographic one.  相似文献   

18.
The hydrogen storage properties of Li(7)VN(4) and Li(7)MnN(4) were investigated both by experiment and by density functional theory calculations. Li(7)VN(4) did not sorb hydrogen under our experimental conditions. Li(7)MnN(4) was observed to sorb 7 hydrogen atoms through the formation of LiH, Mn(4)N, and ammonia gas. An applied pressurized mixture of H(2)/Ar and H(2)/N(2) gases was helpful to mitigate the release of NH(3) but could not prevent its formation. The introduction of N(2) also caused weight gain of the sample by re-nitriding the absorbed products LiH and Mn(4)N, which correlated with the presence of Li(2)NH, LiNH(2), and Mn(2)N detected by X-ray diffraction. While our observed results for Li(7)VN(4) and Li(7)MnN(4) differ in detail, they are in overall qualitative agreement with our theoretical work, which strongly suggests that both compounds are unlikely to form quaternary hydrides.  相似文献   

19.
Electron Paramagnetic Resonance (EPR) and optical absorption spectra of Cr3+ ions doped in single crystals of zinc maleate tetrahydrate (ZMTH) have been studied at room temperature (300 K). The EPR spectra exhibit a group of three fine structure transitions, characteristic of the Cr3+ ion. From the observed EPR spectra, the spin-Hamiltonian and zero-field splitting parameters have been determined. The optical absorption spectrum exhibits two broad bands characteristic of Cr3+ ions in octahedral symmetry. From the observed spectrum, the crystal field parameters have been evaluated.  相似文献   

20.
采用等温蒸发平衡法研究了四元体系K2B4O7-Na2B4O7-Li2B4O7-H2O在273 K时的介稳相平衡及平衡液相的密度. 研究发现该四元体系为简单共饱和型, 无复盐及固溶体形成, 根据溶解度数据绘制了相图, 相图中有一个共饱点E, 三条单变度曲线E3E, E2E, E1E; 三个平衡固相分别为K2B4O7·4H2O、Na2B4O7·10H2O 和LiBO2·8H2O. 并简要讨论了实验结果.  相似文献   

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