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1.
Czesłlaw Rudowicz 《Journal of Physics and Chemistry of Solids》1977,38(11):1243-1251
The paper deals with the spectroscopic and magnetic properties of Fe2+ ions in FeF2. The microscopic spin Hamiltonian theory for Fe2+ in crystalline environments with second-kind orthorhombic symmetry is considered. Explicit formulas for the parameters B0(2)(D),B2(2)(E), gx, gy, gz and, for the first time in the literature, the fourth-order parameters B0(4), B2(4) and B4(4), are derived. Using semi-empirical data for the 5D-term energy levels of Fe2+ ion in FeF2, the pressure dependence of the parameters Bq(k) in the region from 0 to 133 kbar is discussed. The relative role of the fourth-order parameters with respect to the second-order ones is found to increase strongly with pressure (e.g. in the region studied, D increases only by a factor of 3, whereas B0(4) increases by a factor of nearly 20). The magnetocrystalline anisotropy of FeF2; is considered in the strong anisotropy model taking into account the fourth-order spin Hamiltonian terms. The uniaxial anisotropy constants K1 and K2 are derived theoretically and their pressure dependence is discussed quantitatively. The theory and numerical results of this paper are useful with regard to Fe2+ in other isomorphic fluorides, namely: MgF2, ZnF2, VF2 and MnF2. It is found that the fourth-order spin Hamiltonian parameters are accessible to experimental detection from spectroscopic studies on Fe2+ in non-magnetic fluorides and magnetic studies on Fe2+ : MnF2 and FeF2, preferably under high pressure. 相似文献
2.
We study the electronic structures and magnetism of SrFe0.5Ru0.5O2 by first-principles calculations in the framework of density functional theory (DFT) with generalized gradient approximation plus on site repulsion (GGA+U). The DFT calculations were carried out with ten kinds of Fe-site doping form. Calculations show that the d-orbital electronic configurations of Fe2+ and Ru2+ ions are (dz2)2(dyzdxz)2(dxy)2(dx2−y2)1 and (dz2)2(dyzdxz)3(dxy)1(dx2−y2) , respectively, which are independent of the doping form. The degenerated (dxzdyz) orbitals of Ru2+ ions are occupied by three electrons, so it gives rise to the Jahn–Teller distortion. The calculated magnetic moments of Fe2+ and Ru2+ ions are 3.7 μB and 1.6 μB, respectively. The exchange parameters including nearest neighbor (NN) ions and next nearest neighbor (NNN) ions are calculated by using Heisenberg model and the magnetic frustration in the ordered structure is explained by the competition of the exchange parameters. We also study the external pressure effect on the compound. A pressure-induced orthorhombic to tetragonal structure transition accompanied by an insulator to half-metal transition and an antiferromagnetic (or spin glass) to ferromagnetic state transition is observed. 相似文献
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5.
The study of thermally induced depolarization (TD) in crystals of calcium fluoride doped with oxygen reveals the existence of nearest-neighbour (nn) dipolar complexes comprising substitutional oxide ions (Os2?) and fluoride ion vacancies (Fv?) on nn sites. Evidence for this relaxation is seen in TD experiments both on pure calcium fluoride doped with oxygen and on Na+ doped CaF2 crystals that had been heated in air. Similar measurements on CaF2: Y3+, O2? reveal six separate relaxations, two of which are due to Ys3??Fi? complexes that do not involve oxygen, one is due to Os2??Fv? dipoles, and one is t the T1 complex, Ys3+ (O2?)4(Fv?)3. The remaining two relaxations were not identified but are probably d larger defect clusters. 相似文献
6.
Polarization labeling spectroscopy is used to simplify the visible absorption spectrum of NO2. State-selected spectra of the 2B2-2A1 transition in the range 16 600–17 000 and 17 350–17 850 cm?1 are developed using a narrow-band pump operated (1) near 545 nm, where the pumped transitions also belong to the 2B2 system, and (2) near 436 nm on a selected transition of the 2B1-2A1 (Douglas-Huber) band system. Rotational analyses are given for the Ka = 0 and Ka = 1 subbands of 11 vibronic bands and limited observations reported for the Ka = 0 or 1 manifold of a further 8 bands. Polarization-labeling experiments within the 2B1-2A1 band system are also described. 相似文献
7.
O.J. Żogal B. Nowak W. Wolf P. Herzig 《Zeitschrift für Physik B Condensed Matter》1996,101(2):205-210
The spin-lattice relaxation rates (T 1e T)?1 of transition metal nuclei 45Sc, 49Ti, 51V and 93Nb in cubic dihydrides ScH2, TiH2, VH2 and NbH2 are calculated on the basis of scalar-relativistic self-consistent LAPW band structure calculations. It is found that the s and p electron contributions to the relaxation rates are negligibly small for all the hydrides studied here due to their very low partial densities of electron states at the Fermi level. The d- orbital contributions are dominant and the core polarization and d-dipolar contributions play a minor role. The theoretical relaxation rates reproduce the experiments very well for ScH2 and TiH2 but less satisfactory for VH2 and NbH2. The experimental data were taken from our earlier studies and the results of additional measurements on 93Nb in NbH2 are reported. These have been made in the 30–292K temperature range and at a magnetic field of 7 T. 相似文献
8.
P. J. Daly P. Kleinheinz R. Broda S. Lunardi H. Backe J. Blomqvist 《Zeitschrift für Physik A Hadrons and Nuclei》1980,298(3):173-185
The yrast states of148Dy and149Dy have been studied by γ-ray and conversion electron measurements in (α, xn) and (16O,xn) reactions on enriched152Gd and135Ce targets. Level schemes to above 4 MeV for the two nuclei are reported. The πh 2 11/2 spectrum identified in148Dy and the πh 11/2 effective chargee eff=1.52±0.05e, derived from the measuredE2 transition rate between the (πh 2 11/2) 10+ and 8+ states, are discussed and compared with results for other two-particle nuclei. The yrast cascades in148Dy and149Dy continue above the (πh 2 11/2) 10+ and πh 2 11/2 vf 7/2) 27/2? states by ~ 1 MeVE1 transitions de-exciting the lowest members of octupole multiplets built on these states. The energy shifts for the observed members of the πh 2 11/2 × 3? multiplet are analyzed in terms of twoparticle-phonon exchange coupling using an empirical coupling strength extracted from the one valence particle nucleus147Tb. The dominantvf 7/2×3? character of low-lying 13/2+ isomers in149Dy and otherN=83 nuclei is emphasized. 相似文献
9.
Elastic scattering data and inelastic excitation of the lowest 2+ state in 18O from 120 MeV 18O incident on 208Pb are analyzed in coupled channels including couplings to the second 2+ state of 18O. This analysis favors the positive sign for the product of the four E2 matrix elements, p4 = M0121,M0122M2122M2121 where Mij = ?〈i∥M(E2)∥j〉. This is in agreement with shell-model calculations. 相似文献
10.
The g factors of a tetragonally-compressed Cu2+ center in NaCl: Cu+ crystal X-irradiated at room temperature are calculated from the high-order perturbation formulas based on the two-mechanism model. In the model, the contribution to g factors from both crystal-field (CF) and charge-transfer (CT) mechanisms are included. The calculations are based on the defect model that the tetragonally-compressed Cu2+center is assigned to the Cu2+ ion (which is caused by Cu+ ion (at the Na+ site) irradiated by X-ray) associated with a nearest Na+ ion vacancy VNa along C4 axis due to charge compensation. From the calculations, the g factors g|| and g⊥ are explained and the defect structure (charactering by the displacement ΔZ of the Cl− ion intervening in Cu2+ and VNa) of the Cu2+ (or Cu2+-VNa) center is obtained. The results are discussed. 相似文献
11.
Potential surfaces of the CO2 molecule for the ground and excited 3 B 2, 1 B 2 electronic states are calculated by quantum chemistry methods. The calculation of the spin-orbit coupling in the molecule shows a large the matrix element, which removes the prohibition for the dissociation-recombination process CO2(X 1Σ) + M ? CO(X 1Σ) + O(3 P) + M. The barrier on the potential curve for 3 B 2, the energy of which exceeds the limit of dissociation into components in the ground states, explains the data on the dissociation and recombination energies measured in experiments with shock tubes. The absorption cross section of CO2 molecules in the UV spectral region measured at high temperatures allowed us to plot branches of potential curves near their minima for two upper singlet states assigned to the 1 B 2 and 1 A 2 symmetry. 相似文献
12.
Effect of anions on the phase stability of γ-FeOOH nanoparticles and the magnetic properties of gamma-ferric oxide derived from lepidocrocite 总被引:1,自引:0,他引:1
C. Sudakar 《Journal of Physics and Chemistry of Solids》2003,64(12):2337-2349
The effect of anions such as Cl−, SO42−, and HPO42− on the phase stability of FeOOH (α or γ) during precipitation is investigated. Oxidation of Fe(OH)2·xH2O from FeCl2 solution with high Cl− concentration ([Cl−]/[Fe]=RCl≥8) or (NH4)2Fe(SO4)2 (FAS) with [HPO42−]/[Fe]=RP≥0.02 yields phase-pure γ-FeOOH. In the medium ranges of RCl and RP, mixed phases of α-FeOOH and γ-FeOOH are obtained. Replacement of OH− by Cl− with the bridging cations or strongly bonded HPO42− ions in the matrix of the intermediate phase (Fex2+Fey3+(OH)2x+2y−nz·xH2O(A)zn−, where A is anions such as Cl−, SO42−, HPO42−, etc.), promoted the lower density γ-FeOOH. However, the particles are less developed and have poor crystallinity as evidenced from transmission electron microscope and thermogravimetry-differential thermal analysis of the precipitates. Whereas, monophasic, uniformly sized, nano-lath shaped particles with high aspect ratio >10 are obtained when morphology-controlling cation additives such as Pt4+, Pd2+ or Rh3+ are present in FeCl2 (RCl≥8) solution. Preferential adsorption of additives on (0k0) and (h00) planes limits the growth in the perpendicular directions leading to high aspect ratios. The effect of these additives are suppressed by the phosphate ion, a strong complexing ligand, giving rise to fibrous aggregate with the length of individual particles as small as 10-30 nm. While most of the Cl− ion is removed from the final precipitates on washing, phosphate remained as HPO42− as evidenced from IR absorption spectra. Maghemite obtained by dehydroxylating γ-FeOOH contains randomly distributed micropores bringing in the relaxation effects of spins on the surface atoms as deciphered from Mössbauer spectroscopy. This leads to the low σs (44-48 emu/g) and Hc (120-130 Oe) for γ-Fe2O3−δ particles. Whereas nearly pore-free single crystalline particles obtained by reduction followed by reoxidation has high value of σs (73 emu/g) and Hc (320 Oe), which decreases to 30 emu/g and 75 Oe, respectively, for nanoparticles obtained from phosphate stabilized lepidocrocite. The mobility of iron ions and counter mobility of vacancies during the topotactic transformation of γ-FeOOH to magnetite to γ-Fe2O3−δ renders the particles pore-free. 相似文献
13.
N.B. Durusoy M. Baubillier R. George M. Goldberg A.M. Touchard N. Armenise M.T. Fogli-Muciaccia A. Silvestri 《Physics letters. [Part B]》1973,45(5):517-520
We have studied the I=2, ππ scattering using the classical Chew-Low extrapolation method. Results are given on the cross sections and the phase shifts δ02, δ22 and δ42 up to 2.2. GeV. δ02 values are -7.8 ? 3.0° at the Ko mass, -15. ? 1.5° at the ? mass and -29. ? 2.2° of the fo mass. Above the fo mass |δ02| decreases. 相似文献
14.
The EPR spectra of the (BaF2)1 ? x (CeF3) x system are studied for the concentrations x = 0, 0.001, 0.002, 0.005, 0.01, and 0.02. The appearance of new tetragonal centers is detected beginning from x = 0.002, the intensity of these centers being maximal at x = 0.01. The (CaF2)1 ? x ? y (CeF3) x (YF3) y double solutions with x = 0.001 and y from 0 to 0.02 are also studied. In addition to the ordinary tetragonal center, beginning from y = 0.001, a new tetragonal center appears with the same structure as in the previously studied mixed crystals based on BaF2—namely, the Ce3+-□-R3+ chain elongated along the fourfold axis substitutes the Ca2+-Ca2+-Ca2+ and Ba2+-Ba2+-Ba2+ chains in regular CaF2 and BaF2 crystals (□ is the cation vacancy, and R3+ is the Ce3+, La3+, or Y3+ trivalent ion). 相似文献
15.
J.A. Tossell 《Journal of Physics and Chemistry of Solids》1980,41(10):1047-1052
The Self-Consistent-Field Xα Scattered Wave Cluster MO method is used to calculate molecular orbital energy level diagrams for O2, O2?, O22?, S2, S22?, Se22?, P24?, As24? and AsS3?. Calculated energies are in good agreement with those measured by photoemission spectroscopy for O2, S2, S22? in ZrS3, Se22? in ZrSe3 and P24? in TiP2. For O2? the calculated energy of the πu → πg transition agrees fairly well with that of the UV absorption observed in LiO2. The predicted photoemission spectrum of O22? is consistent with a preliminary study on BaO2. Calculated valence region widths in peroxides are found to be significantly greater than the calculated oxygen atomic valence s-p separation while valence widths for the other anions closely match atomic valence s-p splittings. This effect arises from the instability of the peroxide antibonding orbitals which correlates with the absence of dsun peroxides and Superoxides. Calculations on a Cin2v geometry FeO6su9? cluster show that the difference in energy of O2p nonbonding and Fe3d crystal field type orbitals drops sharply as an O-O edge is contracted, providing a mechanism for Fe3+ → Fe2+ reduction at high pressure. 相似文献
16.
K.K. Innes S.J. Jackling T.W. Tolbert 《Journal of Quantitative Spectroscopy & Radiative Transfer》1976,16(5):443-450
Line positions and widths of the B3Πo+u?X1Σ+g electronic transitions of chlorine and bromine gases are measured in absorption as functions of pressure by means of a scanning Fabry-Perot interferometer spectrometer (resolving power > 106). No dependences on quantum numbers are detected. Deconvolutions of measured full-widths-at-half-maxima (FWHM) reveal collision broadening for pressures between 1 and 225 torr. The ratio of self-broadening to shift is always less than that expected for a van der Waals interaction in the impact approximation, namely -2.77. Accordingly, the Lennard-Jones potential is used to determine the effect of the electronic transitions on C6 and C12, and there are found 14 and 6% changes in C6 for Cl2 and Br2, respectively. If, instead, one uses the self-broadening only, and a pure van der Waals interaction, the changes are 6 and 5%. Because the effects are in either model unexpectedly small, comparisons are made with less complete measurements (from the literature) for self-broadening in I2, the B1Σ+g?X3Σ-g system of O2 and the B′Σ+g?X1Σ+g system of HD, and for foreign-gas broadening in the A1Π?X1Σ system of A1H and the A̋1A2(π1, n)?X̋1A1 system of H2CO as well as the HD system. 相似文献
17.
Optical pumping with theD 2 line is used to study the depolarization of the first excited2 P 3/2 states of alkaline earth ions and Yb+ ions in collisions with rare gas atoms. The deorientation cross sections for the even isotopes of Ba+ and Yb+ ions are obtained (in units of 10?16 cm2): rare gas He Ne Ar Kr Xeσ 1 (Ba+ 6p 2 P 3/2) 79(11) 89(13) 123(18) 152(22) 204(30)σ 1 (Yb+ 6p 2 P 3/2) 60(10) 62(9) 107(18) 133(17) 167(37) The cross sections are discussed in comparison with theoretical calculations and those of isoelectronic atoms. The comparison of the2 P 3/2 relaxation of even and odd (I=3/2) isotopes of Ba+ allows to draw conclusions on the nature of the depolarization interaction. 相似文献
18.
M. A. Khodorkovskiĭ A. A. Belyaeva L. P. Rakcheeva T. O. Artamonova P. Yu. Serdobintsev A. A. Pastor A. S. Kozlov S. V. Murashov A. Z. Devdariani R. Hallin K. Siegbahn 《Optics and Spectroscopy》2006,100(4):497-509
The (2 + 1) photoionization mass spectra of Xe2 molecules are studied in a supersonic jet upon excitation by laser radiation in the energy range 80321.3–77821 cm?1, corresponding to the dissociation of the Xe2 molecule into atoms Xe(1 S 0) + Xe*(6p, 5d). Several vibrational progressions are observed, which are attributed to two-photon transitions of Xe2 from the ground state to the excited states of the O + g, 1g, and 2g symmetries. Based on the analysis of these progressions, the molecular constants of a number of excited states of Xe2 are estimated. 相似文献
19.
The deuteron elastic form factors are calculated within the Bethe-Salpeter approach with separable interaction. The charge, quadrupole, and magnetic form factors [F C(q 2), F Q(q 2), and F M(q 2), respectively]; the structure functions A(q 2) and B(q 2); and the tensor polarization components T 20(q 2, T 21(q 2), and T 22(q 2) are investigated up to ?q 2=50 fm?2. The role of relativistic effects is discussed, and a comparison with nonrelativistic calculations is performed. The effect of the neutron form factors on the deuteron form factors and especially on tensor polarization components is discussed too. 相似文献
20.
The time-differential attenuation coefficients for randomly fluctuating interactions in isotropic systems are shown to be of the simple exponential type (well known from the first order treatment of Abragam and Pound) fort?Τ c , notwithstanding the strength of 〈Ω2〉1/2Τ c . Explicit expressions for the relaxation constant are given which are strongly dependent on the strength of 〈Ω2〉1/2Τ c and on the type of interaction but prove to be virtually independent of the stochastic model assumptions. 相似文献