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1.
The bivalent chromium impurity centers in CdF2 and CaF2 crystals are investigated using electron paramagnetic resonance (EPR) in the frequency range 9.3–300 GHz. It is found that Cr2+ ions in the lattices of these crystals occupy cation positions and form [CrF4F4]6? clusters whose magnetic properties at low temperatures are characterized by orthorhombic symmetry. The parameters of the electron Zeeman and ligand interactions of the Cr2+ ion with four fluorine ions in the nearest environment are determined. The initial splittings in the system of spin energy levels of the cluster are measured.  相似文献   
2.
Emission Mössbauer (nuclear gamma-resonance) spectra of237Np resulting from the alpha-decay of241Am in solid solutions AmO2–ThO2 and AmO2–UO2 prepared by precipitation from LiF–NaF eutectic melts under fluorine-oxygen exchange were first investigated in the temperature range from 77 to 296 K. The resonant absorbers are NpO2 and NpAl2. The possibility is stated of managing the form of the emission Mössbauer spectra of237Np in dioxides by the directed change of the matrix stoichiometry or by its irradiation by visible light. At temperatures from 77 to 230 K the authors measured for the first time the NGR absorption spectra of237Np in solid solution NpO2–ThO2 with various concentrations of neptunium dioxide. An increase of the absorption line width (approximately by a factor of 4) with a decrease in the NpO2 contents (to 10 mol.%) was explained by the influence of fast electron exchange between Np4+ and Np5+ states observed in the NpO2–ThO2 solid solution at low concentrations of neptunium dioxide.  相似文献   
3.
Paramagnetic centers of three types are found in SrF2: Fe(0.2 at. %) crystals. Two types are observed in the untreated crystals, and the third type appears only in the crystals irradiated by x-rays. The EPR spectra of one type of centers in a nonirradiated crystal and of the centers that appear after irradiation are described by the orthorhombic Hamiltonians with an effective spin S eff = 5/2. In both cases, the centers are observed at 4.2 and 77 K. The principal axes of the spin Hamiltonians for them are along the 〈001〉, 〈1 \(\overline 1 \) 0〉, and 〈110〉 axes. However, the fine-structure parameters of their EPR spectra differ significantly. An analysis of the superhyperfine structure (SHFS) of the EPR spectra shows that the radiation center forms through substitution of a Fe2+ ion for a Sr2+ cation. Under x-ray irradiation, the Fe2+ ion transforms into the Fe3+(6 A 1g ) state and is displaced to an off-center position along the C 2 axis of its coordination cube. The absence of a SHFS in the EPR spectra of the orthorhombic centers in a nonirradiated crystal makes it impossible to determine their molecular structure unambiguously. The most probable model is proposed for this structure. The EPR spectra of centers of the third type were observed only at 4.2 K, and the structure of these centers was not studied.  相似文献   
4.
JETP Letters - The temperature dependences of attenuation and the velocity of ultrasonic waves at frequencies of 26–158 MHz in a CaF2 fluorite crystal at the substitution of...  相似文献   
5.
We shall investigate the initial stage of the impact of an axisymmetric fluid jet having a plane face on a rigid obstacle. An example of a numerical calculation by a finite-difference method [1] is cited.  相似文献   
6.
The influence of local distortions on the structure and properties of copper and silver impurity Jahn-Teller complexes in mixed crystals, namely, CaxSr1?x F2: Me 2+ and Sr1?x BaxF2: Me 2+ (0≤x≤1, Me 2+=Cu2+ or Ag2+), is investigated using electron paramagnetic resonance (EPR) spectroscopy at frequencies of 9.3 and 37 GHz in the temperature range 4.2–250 K. Local distortions of the tensile and compressive types are induced by Ca2+, Sr2+, and Ba2+ impurity ions incorporated into the first or second coordination sphere of the cationic environment of the Me 2+ impurity ion during crystal growth.  相似文献   
7.
The local structure of titanium pair centers in SrF2: Ti crystals is investigated using electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) spectroscopy. It is found that titanium pair centers with spin moment S=2 and tetragonal symmetry of the magnetic properties are formed in SrF2: Ti cubic crystals under certain growth conditions and during annealing. The tensor components of the fine and ligand hyperfine structures in the EPR and ENDOR spectra are determined. A model of the Ti+-Ti3+ paramagnetic dimer is proposed. This model provides an adequate interpretation of both the ferromagnetic nature of the exchange interaction and the observed displacements of four ligands in the first coordination sphere of titanium impurity ions in directions perpendicular to the impurity ion-ligand bonds.  相似文献   
8.
Heats of solution and enthalpies of donor-acceptor interaction of several organic O-bases with SbCl5 in dichloroethane, benzene, nitrobenzene, butyl acetate, and acetone were determined by calorimetry. The correlation between the interaction enthalpies and the donor number of O-base is linear in all the solvents. The structure of an inert solvent does not affect the slope of the dependences and is manifested in mutual arrangement of the curves, with the shift being proportional to the donor number of the solvent.  相似文献   
9.
Crystals of CaF2: Cu (with a copper impurity content higher than 0.1 at. %) grown by the Czochralski method from a melt in a mixed helium-fluorine atmosphere are investigated using electron paramagnetic resonance (EPR) spectroscopy. It is found that the crystals contain paramagnetic centers whose magnetic properties at low temperatures are identical to those of [CuF4F4]6? (S=1/2) single centers. The magnetic properties of the centers exhibit a qualitative change in the temperature range 77–300 K. These changes are described within a model according to which the center is treated as a cluster composed of three [CuF4F4]6? impurity complexes involved in exchange interactions and interactions occurring in the field of Jahn-Teller lattice distortions.  相似文献   
10.
Tetragonal paramagnetic centers with spin S = 7/2 were detected in x-ray-irradiated BaF2: Fe (cFe ≈ 0.002 at. %) crystals using the EPR method. Electronic transitions between the |±1/2〉 states of a Kramers doublet were observed in the X and Q ranges. In the EPR spectra of the tetragonal centers, a ligand hyperfine structure (LHFS) was observed corresponding to the interaction of the electron magnetic moment of the tetragonal center with eight equivalent ligands. The large spin moment, significant anisotropy of the magnetic properties, and the characteristic LHFS indicate that the tetragonal center is a Fe1.5+?Fe1.5+ dimer in which the two iron ions are bound via superexchange interaction. It is assumed that, before crystal irradiation, this dimer was in the Fe3+(3d5)?Fe+(3d7) state.  相似文献   
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