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1.
EPR of Gd3+ doped in Ce2M3(NO3)12.24H2O (M″ = Mg, Zn, Co) single crystals has been studied at various temperatures from room temperature to 77 K using ∼ 9.45 GHz EPR spectrometer. The observation of resolved Gd3+ spectra at room temperature in Ce3Co2(NO3)12.24H2O has been interpreted in terms of a random modulation of the interaction between the Gd3+ and the Co2+ ions by the rapid spin-lattice relaxation of Co2+ ions. It is found that the effective spin-lattice relaxation time T1T−n where n = 1.85 (Bz axis) and n = 1.75 (Bz axis) if 103 < T < 283 K.  相似文献   

2.
EPR studies of [Mg(H2O)6]BF6 (B=Si, Ge) crystals are performed by using Mn2+ paramagnetic probes. The temperature dependence of the EPR spectra shows that the crystals undergo a ferroelastic phase transition to a monoclinic phase. In both systems the ferroelastic phase transition is preceded by intermediate states. The spin Hamiltonian parameters determined in the low and high temperature phases of the systems are useful to precise some aspects of the local atomic displacements involved in the intermediate states. The nature of this state is analyzed in the framework of different models as well.  相似文献   

3.
The electron paramagnetic resonance spectra of Cu2+ in [Cd(sac)2(H2O4]·2H2O and [Cd(sac)2(HydEt-en)2] (HydEt-en=N-(2-hydroxyethyl)-ethylenediamine) single crystals and powder were examined at room temperature. A detailed study of the spectra of the compounds indicates the replacement of Cd2+ in the host compounds with Cu2=. [Cd(sac)2(H2O)4]·2H2Oshows the presence of two sites for Cu2+ and [Cd(sac)2(HydEt-en)2] has a single site. The principal values for theg-tensor and the hyperfine tensor for Cu2+ in the two compounds were obtained. The Cu2+ ion was found to be mostly in the 3dx 2y 2 orbital and the ground-state wavefunction of [Cd(sac)2(HydEten]2] was constructed.  相似文献   

4.
The temperature and angular dependences of the EPR spectra of Mg[H2O]6SiF6:Mn2+ crystal were investigated in order to clarify the successive phase transitions and existence of the incommensurate phase. Five successive phase transitions were found to occur, and phase II was found to be incommensurately modulated. The modulated structure is caused mainly by the vibrational displacement of the Mg[H2O]2+ 6 ion along the c-axis. The soliton density of this phase is almost independent of temperature and remains equal to unity.  相似文献   

5.
The IR spectra and polarization Raman spectra of Kal(SO4)2·12(H2O) and Kal(SO4)2·12[H2O)0.3(D2O)0.7] crystals at 93 K and room temperature have been obtained experimentally. The vibrational spectra of structural elements of potassium alum — the complexes [Al(H2O)6 3+ and [Al(D2O)6]3+ — have been calculated. The vibrational spectra have been interpreted based on the calculation and factor-group analysis data. The spectral data obtained point to the fact that, in the crystals considered, the sulfate ions are partially disordered and there exist two crystallographically different types of water molecules.  相似文献   

6.
The single‐crystal Raman spectra of minerals brandholzite and bottinoite, formula M[Sb(OH)6]2•6H2O, where M is Mg+2 and Ni+2, respectively, and the non‐aligned Raman spectrum of mopungite, formula Na[Sb(OH)6], are presented for the first time. The mixed metal minerals comprise alternating layers of [Sb(OH)6]−1 octahedra and mixed [M(H2O)6]+2/[Sb(OH)6]−1 octahedra. Mopungite comprises hydrogen‐bonded layers of [Sb(OH)6]−1 octahedra linked within the layer by Na+ ions. The spectra of the three minerals were dominated by the Sb O symmetric stretch of the [Sb(OH)6]−1 octahedron, which occurs at approximately 620 cm−1. The Raman spectrum of mopungite showed many similarities to spectra of the di‐octahedral minerals, supporting the view that the Sb octahedra give rise to most of the Raman bands observed, particularly below 1200 cm−1. Assignments have been proposed on the basis of the spectral comparison between the minerals, prior literature and density functional theory (DFT) calculations of the vibrational spectra of the free [Sb(OH)6]−1 and [M(H2O)6]+2 octahedra by a model chemistry of B3LYP/6‐31G(d) and lanl2dz for the Sb atom. The single‐crystal spectra showed good mode separation, allowing most of the bands to be assigned to the symmetry species A or E. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

7.
Mg[Pt(CN)4]·7H2O belongs to the class of tetracyanoplatinates(II) which crystallize in columnar structures. In different Mx[Pt(CN)4yH2O (MCP) single crystals the in-chain Pt-Pt-distance R varies between 3.67 Å (NaCP) and 3.15 Å (MgCP). Two optical transitions can be observed in polarized emission with the electric field vector E either parallel or perpendicular to the columnar (c)-axis. Polarized emission spectra of MgCP are recorded under hydrostatic pressure up to p ≈ 18 kbar (at 295 K). The transition energy v?6 can be tuned from 17,600 cm-1 to about 12,000 cm-1 (2.18-1.48 eV). The pressure induced red shift for the two transitions is: E 6 c: dv?6/dp = -320±20 cm-1/kbar, Ec: dv?/dp = -270±20 cm-1/kbar. These values are discussed in the context of the known functional relationship (for ambient conditions) between v? and R.  相似文献   

8.
Infrared and Raman spectra (10–3100 cm?1) of the layered ZnPSs compound and of intercalates with [Co(η5 ? C5H5)2+] and [Cr(η6 ? C6H6)2+] cations in the polycrystalline state have been recorded 300–10 K temperature range. A complete assignment of the spectra is proposed in terms of PSs group motions, Zn2+ ion translations and [Co(η5 ? C5H5)2+] or [Cr(η6 ? C6H6)2+] internal vibrations. New low frequency for the [Co(η5-C5H5)2+] intercalate at low temperature are assigned to librational and torsional modes of C5H5 rings. Moreover, the preresonance Raman spectra of this intercalate show a selective enhancement for the metal-ligand vibrations when the charge transfer band of the cobalticenium is approached. One concludes that guest molecules are intercalated under their cationic form, are weakly interacting with the host lattice and seem to be dynamically disordered at room temperature.  相似文献   

9.
EPR investigations using Cu2+ ion as a probe have been performed on supersaturated sucrose solution with percent concentration c = 66 as a function of temperature T, and at room temperature as a function of c. The motionally averaged spectrum of [Cu(H2O)6]2+ was used to monitor the changes in intermolecular interactions that occur as a function of [c, T]. A drastic increase in the line width, symptomatic of increase in the rotational correlation time of [Cu(H2O)6]2+, is observed between 293 and 288 K. The motionally averaged spectrum disappears below 281 K. The motionally averaged spectrum is also absent in the room temperature spectra of the solution with c= 85. Even in the [c, T] range where [Cu(H2O)6]2 is found to be nearly static, these molecules appear to have an orientational fluctuation manifesting in the m 1 dependence of the line width of the parallel component.  相似文献   

10.
Parameters of the local coordination of Co2+ and Ni2+ cations in polymer matrices are determined by XAFS spectroscopy at the K edges of the corresponding elements. Ion-exchange complexes of Ni2+ and polymethacrylate, low-molecular acrylamide complexes [M(CH2=CHC(O)NH2)6](NO3)2 (M = Co or Ni), and products of their thermal polymerization are investigated. The final results are in agreement with the octahedral coordination of M atoms (average distances, 2.10–2.11 (Co-O) and 2.05–2.06 Å (Ni-O).  相似文献   

11.
The vibrational spectra of Eu[Co(CN)6]·4H2O and luminescence spectra of Eu3+ in this compound, using 355 nm excitation at temperatures down to 10 K, have been assigned. A clear distinction is made between the n=5 and 4 members of the Ln[M(CN)6nH2O series from the vibrational spectra. The electronic spectra show prominent vibronic structures, particularly for the 5D07F2 sideband. A resonance occurs between the transitions 5D07F1(III) and 5D07F0+ν(Eu−N). A crystal field analysis of the derived energy data set is presented for Eu3+ in eight coordination geometry.  相似文献   

12.
The EPR spectra of the Mn2+ ion in crystals of the perchlorate hexahydrates Zn(ClO4)2 · 6H2O, Mg(ClO4)2 · 6H2O, and Cd(ClO4)2 · 6H2O were studied in the temperature range 77–320 K under hydrostatic pressure. It is shown that the octahedron of six molecules H2O surrounding this paramagnetic ion is contracted along the c axis and that pressure decreases this distortion. The second-order phase transition that occurs near 200 K in the perchlorates and in other crystal hydrates is shown to be associated with changes in the bonds in the nearest ligand environment. As the pressure is increased, the phase-transition temperatures shift and the perchlorate crystals tend to a single-phase state. The low-temperature phase is assumed to disappear as the pressure increases, and this phase exists in a closed T-P region in the phase diagram. As the pressure increases, the character of the high-temperature transition in the Cd(ClO4)2 · 6H2O changes: the jumplike transition at T 1 with a 1-K hysteresis changes into a smooth transition and then disappears as the pressure increases further.  相似文献   

13.
Chlorides, nitrates and sulfates of M (M=Mn, Fe, Co, Ni and Zn) were dissolved in aqueous solutions of SnF2 at M/Sn molar ratios of 0.5 to 3. No HF was used. The solutions were allowed to evaporate in air. Very small amounts of hexagonally shaped crystals of unknown materials were obtained for M=Mn, Co, Ni and Zn. Fe did not yield this phase. X-ray powder diffraction gives identical patterns for the four materials, which are therefore most likely isostructural, and showed that the products are not MSn2F6·6H2O or MSnF6·6H2O. Tin-119 Mössbauer spectroscopy gives a single line at negative isomer shift, characteristic of [Sn(IV)F6]2– ions.  相似文献   

14.
Alkaline hexafluorostantanate red phosphors Na2SnF6:Mn4+ and Cs2SnF6:Mn4+ are synthesized by chemical reaction in HF/NaMnO4 (CsMnO4)/H2O2/H2O mixed solutions immersed with tin metal. X-ray diffraction patterns suggest that the synthesized phosphors have a tetragonal symmetry with the space group D4h14 (Na2SnF6:Mn4+) and a trigonal symmetry with the space group D3d3 (Cs2SnF6:Mn4+). Photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and the Raman scattering techniques are used to investigate the optical properties of the phosphors. The Franck-Condon analysis of the PLE data yields the Mn4+-related optical transitions to occur at ∼2.39 and ∼2.38 eV (4A2g4T2g) and at ∼2.83 and ∼2.76 eV (4A2g4T1g) for Na2SnF6:Mn4+ and Cs2SnF6:Mn4+, respectively. The crystal field parameters (Dq) of the Mn4+ ions in the Na2SnF6 and Cs2SnF6 hosts are determined to be ∼1930 and ∼1920 cm−1, respectively. Temperature-dependent PL measurements are performed from 20 to 440 K in steps of 10 K, and the obtained results are interpreted by taking into account the Bose-Einstein occupation factor. Comprehensive discussion is given on the phosphorescent properties of a family of Mn4+-activated alkaline hexafluoride salts.  相似文献   

15.
EPR spectra of the 59Co+2 ion in oriented crystals of Mg(CH3COO)2·4H2O have been measured at 9.4 GHz and a temperature of 4.2 K. The data for each of the two metal ion sites per unit cell are well-described by a spin Hamiltonian for S = 12, I = 72 with gx = 6.13, gy = 389, gz = 2.49 and Ax = 0.0193, Ay' = 0.075, Az' = 0.0032 cm?1. Only the x-axes of the g- and A-tensors coincide. Orientation of the principal directions relative to the crystal axes has been established for the g- and A-tensors at both sites. They are consistent with the weakly ferromagnetic canted antiferromagnetism found in Co(CH3COO)2·4H2O below TN ?85mK.  相似文献   

16.
From a temperature dependent ESR study of Mn2+-doped crystals of M(BF4)2·6H2O, M Zn, Co and Ni, new structural phase transitions have been detected and studied. First order structural phase transitions occur in Co(BF4)2·6H2O at T1 ~ 281K, T2~189 K and T3~172K (during cooling), in Zn(BF4)2·6H2O at T1 ~ 286 K and in Ni(BF4)2·6H2O at T1 ~ 301 K. A continuous phase transition occurs in Co(BF4)2·6H2O at Tp ~ 257 K, in Zn(BF4)2·6H2O at Tp ~ 277 K and in Ni(BF4)2·6H2O at Tp ~ 294 K. The ESR spectral characteristics suggest similarities in the structures of these fluoroborate compounds in the phase above T1 with the room temperature structure of Mg(ClO4)2·6H2O. All these compounds are found to have a tendency to crystallise in a triply-twinned pseudo-hexagonal form, although the unit cell above T1 is found to be orthorhombic. The structural changes related to the water octahedron around the metal at T1 were found to be very small and basically the same for these three compounds. Although the unit cell structure of Fe(BF4)2·6H2O above the first order phase transition temperature T1 was found to be similar to that of the other fluoroborate compounds, the structural changes occurring at T1 appeared to be quite different. The low temperature thermal behaviour differs considerably in the Co, Fe and Zn compounds.  相似文献   

17.
The electron spin resonance of VO2+ is studied in single crystals of Cs2M″ (SeO4)2·6H2O (M″ = Zn, Co) from 290 to 77 K at ~ 9.45 GHz. The line broadening of VO2+ spectra on cooling the Cs2Co(SeO4)2·6H2O crystal is explained on the basis of host spin-lattice relaxation narrowing. T1 for Co2+ is estimated to be ≈ 1.7 × 10?12 sec. at 290 K.  相似文献   

18.
The contributions from modes of switching, sliding, creep, and Debye relaxation of pinned domain walls to the low-frequency magnetic properties of the chiral and racemic molecular ferrimagnets [MnII(HL-pn)(H2O)][MnIII(CN)6] · 2H2O have been separated. It has been found that the chirality of the atomic and spin structures affects the temperatures of the transitions from the sliding mode to the creep mode and from the creep mode to the mode of Debye relaxation. In the chiral crystals, transitions to the creep and Debye relaxation modes have been observed at temperatures T = 7 and 5 K, respectively. In the racemic crystals, these transitions have been observed at temperatures T = 13 and 9 K, respectively, all other factors being equal.  相似文献   

19.
Mössbauer spectra on single crystals of [Fe(H2O)6]K2(SO4)2 in fields from 1.5 T to 5 T at temperatures from 4.2 K to 20 K show considerable line broadenings up to 0.95 mm/s. This broadening strongly depends on the specific line in the spectrum, the temperature, and the strength and direction of the external field. It is shown that these phenomena are due to electronic relaxation rates that are some-what slower (≈10?8 s) than the fast relaxation limit.  相似文献   

20.
Mössbauer studies on Fe(ClO4)2(H2O)6 salt showed anomalous quadrupole splitting around (230 ± 15)°K which we have established to be due to a new type of phase transition from pseudohexagonal to monoclinic system. Exactly similar type of transition was observed magnetically in all the isomorphous Ni2+, Co2+ and Mn2+ perchlorate hexahydrate single crystals at different critical temperatures.  相似文献   

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