Mössbauer studies of PbFe2/3W1/3O3 multiferroics

Mössbauer studies of ceramic samples of the antiferromagnetic perovskite PbFe_2/3W_1/3O₃ have been carried out. It has been established that the temperature of transition to the magnetically ordered state is T _N = 365 K. Iron ions in PbFe_2/3W_1/3O₃ are found to reside in the high-spin Fe³⁺ state. The Fe³⁺ ions occupy inequivalent positions differing in the nearest cation environment, or more precisely, tungsten and iron ions are distributed in a random manner over the sites of the octahedral sublattice. The inequivalent positions arise as a result of the Fe and W ions being statistically distributed over the octahedral sublattice. For T > 0 K, magnetic fields at the nuclei and, hence, the average thermodynamic values of the magnetic moments of Fe³⁺ ions occupying inequivalent positions are different and, at a given temperature, are determined by the number of the nearest magnetic neighbors, with the effective magnetic fields (H _eff) varying differently with temperature. As the temperature is lowered, the fields H _eff level off gradually in response to the effective magnetic fields of iron ions having different numbers of exchange bonds leveling off with decreasing temperature which lowers thermal excitation.     

Adiabatic approximation forW * quantum systems with particles of massm,M as (m/M)1/2→0

The (m/M)^1/20 limit and the adiabatic approximation for a nonrelativistic system consisting of light and heavy particles of massesm,M are studied. The method used involves a standard representation of quantum mechanics, in which the limit above exists. The standard representation is described in some detail, and the Primas-Raggio theorem is derived, which implies that the limit (m/M)^1/20, the heavy-particle system is a static, semiclassical system, i.e., with a commutative algebra of observables. The adiabatic approximation is derived as the leading correction.     

Mössbauer studies of the layered compound 1T-TAS2

We report the temperature dependence in Tantalum Disulfide 1T-TaS₂ of the elastic and inelastic intensities of the first order satellite (1.285, 0, 0.333) and (3, 0, 0.21) near the Bragg peaks (1, 0, 0) and (3, 0, 0), respectively. The phason temperature factor has been measured as a function of temperature from 70 to 295 K using Mössbauer gamma-ray scattering. The high-energy resolution provided by this technique allowed experimental separation of the elastic scattering from the inelastic thermal diffuse scattering. The first order satellite is found to be 15% inelastic. The results were compared with those found by Chapman and Colella obtained by X-ray method (Moret and Colella, Phys. Rev. Lett. 52:652, 1984).     

Subsidiary conditions of the general Gel'fand-Yaglom wave equation based on the representation (1/2,3/2)⊕(−1/2,3/2)⊕(1/2,5/2)⊕(−1/2,5/2)⊕ (1/2,3/2)⊕(−1/2,3/2)

A method is given of obtaining the subsidiary conditions of the second kind of the general Gel'fand-Yaglom wave equation based on the representation (1/2, 3/2)(–1/2, 3/2)(1/2, 5/2)(–1/2, 5/2)(1/2, 3/2)(–1/2, 3/2) and in the presence of an external electromagnetic field by reformulating the wave equation in spinor form. The wave equations accepting these subsidiary conditions form a class defined by a set of simultaneous equations that is not empty.     

Temperature impedance spectroscopy of (1 − x)Na1/2Bi1/2TiO3-xLaMg1/2Ti1/2O3 solid solutions

The dielectric properties of (1 ? x)Na_1/2Bi_1/2TiO₃-xLaMg_1/2Ti_1/2O₃ solid solutions (0 ≤ x ≤ 0.4) were studied over the temperature range 650–1030 K by measuring the impedance spectra over the frequency range 25–10⁶ Hz. The Curie temperature T _C was determined as a function of the composition of the solid solutions. It is shown that T _C decreases linearly with increasing x. The temperature dependences of the dc component (σ_dc) and the polarization component (σ′_ac) of the real part of the conductivity are found. The activation energy for the conductivity σ_dc is shown to increase abruptly as the temperature increases above approximately 770 K for all solid solution compositions. Over the temperature range corresponding approximately to the region of existence of the tetragonal phase of Na_1/2Bi_1/2TiO₃, the polarization component σ′_ac of the solid solutions, as well as that of the pure compound, is anomalously high at low frequencies, which can be due to structural inhomogeneities.     

Study of hypercharge exchange reactions of the type 0−1/2+→2+1/2+ at 4GeV/c

Results are presented for the quasi two-body hypercharge exchange reactions of the type 0^?1/2⁺→2⁺1/2⁺: $$\begin{gathered} \pi ^ - p \to K^0 (1420)(\Lambda ,\sum ^0 ), \hfill \\ K^ - p \to f^0 (1270)(\Lambda ,\sum ^0 ), \hfill \\ K^ - p \to f\prime (1515)(\Lambda ,\sum ^0 ), \hfill \\ \end{gathered} $$ using data from two high statistics bubble chamber experiments. The total and differential cross sections are presented and compared with those obtained for the corresponding vector meson reactions and with simple phenomenological ideas.     

Isotope shift of the 2s ~2S_(1/2)→ 2p ~2P_(1/2,3/2) transitions of Li-like Ca ions

The mass-and field-shift parameters of the two 2 s ~2 S_(1/2)→2 p ~2 p_(1/2,3/2) transitions in the Li-like Ca ions are calculated by using multi-configuration Dirac-Hartree-Fock(MCDHF) and the relativistic configuration interaction(RCI) methods with the inclusion of the transverse photon(Breit) interaction,vacuum polarization and self-energy corrections.In addition,the mass shift and field shift of these two transitions are calculated,where the field shift is calculated by using the evaluated value δr~2 obtained by [Atomic Data and Nuclear Data Tables 99 69(2013)].It is found that the mass shift of Li-like Ca ions is greater than the field shift.     

Measurement of the caesium 6S1/2?8P1/2 transition frequency

The caesium 6S _1/2? 8P _1/2,3/2 transitions at 387.6 nm and 388.8 nm have been observed with a linewidth of <5 MHz by laser spectroscopy. The absolute frequency of the 6S _1/2?8P _1/2 transition was determined to an uncertainty of ±1 MHz using the calibrated rubidium 5S _1/2?5D _5/2 two-photon transition and accurate interferometry. The potential of this caesium transition as a useful secondary frequency standard in blue–UV region is discussed. Received: 7 February 2000 / Revised version: 24 March 2000 / Published online: 24 July 2000     

Recent Experimental Results of HL-1M Tokamak and Progress of HL-2A Project

Recent experimental results of HL-1M tokamak and progress of HL-2A project are presented. Strong fishbone instability was observed during off-axis ECRH. This is first observation of the fishbone instability purely driven by energetic electrons produced by ECRH. The MBI was first proposed and demonstrated on HL-1M. Recently new results of MBI experiment were obtained by increasing the pressure of gas. A stair-shape density increment was obtained with high-pressure multi-pulse MBI just like the density evolution behavior during the multipellet injection. It is shown     

Plasmon-phonon mechanism of nonradiative transition 2S 1/2 → 2P 1/2 in grazing scattering of a hydrogen atom at the surface of a solid

The probability of nonradiative transition 2S _1/2 ?? 2P _1/2 in the case of grazing scattering of a hydrogen atom with an energy on the order of 1 keV at an Au and LiF surface is calculated in the semiclassical theory of nonadiabatic transitions. The transitions are induced by the interaction of the atom with the fields of surface plasmons and optical phonons, respectively. A formalism is developed which makes it possible to exceed the approximation based on the method of electrical images of charges. The value of the probability of scattering at LiF is high enough for experimental observation of the effect. The probability of this transition is determined for the motion of the atom parallel to the metal surface.     

Relativistic many-body calculations of E1, E2, M1, and M2 transitions rates for the 1 s 2 l′ 2 l′ ′ – 1 s 2 2 l lines in Li-like ions

Reduced matrix elements, oscillator strengths, and transition rates are calculated for all allowed and forbidden 1s2l′ 2l′ ′ – 1s ²2l electric dipole (E1), magnetic dipole (M1), electric quadrupole (E2), and magnetic quadrupole (M2) transitions in lithiumlike ions with nuclear charges ranging from Z?=?6 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1, M1, E2, and M2 matrix elements. The calculations start with a Dirac potential and include all possible 1s2l′ 2l′ ′ configurations, leading to seven odd-parity and nine even-parity states. First-order perturbation theory is used to obtain intermediate coupling coefficients. Second-order RMBPT is used to determine the matrix elements, which are evaluated for the 22, 20, 16, and 18 possible E1, M1, E2, and M2 transitions, respectively. A detailed discussion of the various contributions to the energy levels and E1, M1, E2, and M2 matrix elements is given for lithiumlike iron, Z?=?26. The transition energies used in the calculation of oscillator strengths and transition rates are evaluated using second-order RMBPT. Trends of E1, M1, E2, and M2 transition rates as functions of nuclear charge Z are shown graphically for 1s2l′ 2l′ ′ – 1s ²2l transitions.     

Mössbauer study of the HgBa2Ca n−1CunO2n+2 ceramics

The parameters of the electric-field gradient tensor at the copper, barium, and mercury sites in the HgBa₂Ca _n?1Cu_nO_2n+2 lattices (n=1,2,3) have been determined by Mössbauer emission spectroscopy on the ⁶⁷Cu(⁶⁷Zn), ¹³³Ba(¹³³Cs), and ¹⁹⁷Hg(¹⁹⁷Au) isotopes, and calculated in the point-charge approximation. An analysis of these results combined with available ⁶³Cu NMR data showed that the experimental and theoretical data can be reconciled by assuming that the holes originating from defects in the material are localized primarily on the sublattice of the oxygen lying in the copper plane [for HgBa₂Ca₂Cu₃O₈, in the plane of the Cu(2) atoms].     

Holographic cosmology from a system of M2–M5 branes

In this paper, we analyze the holographic cosmology using a M2–M5 brane configuration. In this configuration, a M2-brane will be placed in between a M5-brane and an anti-M5-brane. The M2-brane will act as a channel for energy to flow from an anti-M5-brane to a M5-brane, and this will increase the degrees of freedom on the M5-brane causing inflation. The inflation will end when the M5-brane and anti-M5-brane get separated. However, at a later stage the distance between the M5-brane and the anti-M5-bran can reduce and this will cause the formation of tachyonic states. These tachyonic states will again open a bridge between the M5-branes and the anti-M5-branes, which will cause further acceleration of the universe.     

Mössbauer study of Cu1−xZnxFe2O4 catalytic materials

In the present work, we have synthesized and characterized magnetic nanoparticles of maghemite γ-Fe₂O₃ to study their structural and magnetic properties. For the preparation, magnetite precursor, were oxidized by adjusting the pH = 3.5 at about 80 °C in an acid medium, The mean size of the maghemite particles calculated from the X-ray diffractogram was around 5.7 nm. Mössbauer spectroscopy measurements at room temperature show their superparamagnetic behavior. Furhermore, Mössbauer measurements were carried out at 77 K and 4.2 K in order to find the typical hyperfine fields of the maghemite. Magnetite phase was not found. FC and ZFC magnetization curves measured at 500 Oe indicate a blocking temperature of 105.3 K. The magnetization measurements also show almost zero coercivity at RT. TEM images show nanoparticles with diameter smaller than 10 nm, which are in good agreement with the X-ray pattern and the fitting of the magnetization data.     

Mössbauer and TEM studies of the perovskite system (1-y)La2/3 $$A$$ 1/3TiO3·yLaFeO3

The microscopic nature of the Mössbauer phase analysis has been found as being particularly valuable in testing assumptions suggested by TEM results regarding the microdomain structure and the population of different lattice sites by iron ions in the perovskite system (1-y)La_{2/3 1/3}TiO₃·yLaFeO₃ with 0.04<y < 0.25 ( is an A-site vacancy). This system was found to contain only Fe₃₊-phases which are stable under normal conditions, but moderate heating in vacuo causes a partial reduction of ferric ions to ferrous ions.     

Feature extraction of ship radiated-noise by 1(1/2)-spectrum

1 lntroductionIn ship radiated-noise, there are a series of line spectra and co11til1uous spectra cre-ated b}' vortex flow, turbulence, sparge, impulsion and random vibration. The fOrmersare useful fOr classification alld recognition of ships. But fOr the later. the used infOrmation is only several points located at the outIine of continuous spectrum instead of thedetail xuriety of it. The points represent the \urying trend or shape character. Becausethe continuous spectra are related to lin…     

57Fe hyperfine interactions in M1 and M2 sites of olivine from Omolon meteorite: study using Mössbauer spectroscopy

Study of olivine (Fe, Mg)₂SiO₄ from Omolon meteorite was performed using Mössbauer spectroscopy with a high velocity resolution at 295 and 90 K. Components related to ⁵⁷Fe in crystallographically non-equivalent M1 and M2 sites in olivine were determined and its Mössbauer hyperfine parameters were evaluated at both temperatures. A Fe^2?+?–Mg^2?+? distribution coefficient and a temperature of cation equilibrium distribution for olivine from Omolon were evaluated on the basis of Mössbauer parameters.     

Structural stability,phase transition and dielectric properties of Pb(Mg1/2W1/2)1−xMxO3 (M = Zr,Sn, Ti) ceramics

ABSTRACT

Pb(Mg_1/2W_1/2)_1?xM_xO₃ (M?=?Zr,Sn,Ti) ceramics have been prepared by the conventional ceramic process. Their crystallographic, phase transition and dielectric properties have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer in this paper. The solubility of the tetra-valent cation in Pb(Mg_1/2W_1/2)_1?xM_xO₃ decreases in the sequence of Ti^4+?>?Zr^4+?>?Sn⁴⁺. The doping led to the phase transition from orthorhombic antiferroelectric to cubic paraelectric phase, the microscopic nature of which could be attributed to the contraction of Pb-O₁₂ dodecahedron. A definition of the ordering parameter of the cubic phase was deduced to quantitatively evaluate the B-site ordering degree which decreased with the increase in doping concentration. Anti-site disordering of Mg²⁺ and W⁶⁺ occurred in the high-level doping compositions, which led to the relaxor behavior observed in Ti⁴⁺-doped series with x?=?0.01 composition. Both of the maximum dielectric permittivity and loss in the paraelectric phase increased with the increasing doping concentration.     

关于互感系数M=√L1L2

通常的某些论述表明，似乎两个感应圈的自感彼此不等，它们之间仍可以有Ｍ＝√Ｌ１Ｌ２。本文将提出修正意见。