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1.
DSC and complex impedance studies of the protonic conductor (NH4)4H2(SeO4)3, which undergoes a superionic phase transition of first order at Ts = 378 K show that the activation energy of ionic conductivity d(lg σ)/dt and the ordering enthalpy ΔCp of the crystal are proportional: d(lg σ)/dT = XΔCp/RTs + const, as found for MAg4I5 crystals undergoing a second-order superionic phase transition. Thus the short-range order environment of the species involved in fast-ion transport plays the main role in the superionic phase transition. This is also supported by the value of the entropy change at Ts, ΔS = 43 J/mole·K. A new metastable phase was found to be induced on heating the (NH4)4H2(SeO4)3 crystal above Ts. 相似文献
2.
An experimental study was made of the changes in the normal and anomalous Hall constants R0 and Rs, respectively, the internal saturation induction Bs, and the resistivity ? during the ordering of quasibinary Ni3Mn-Ni3Fe and Ni3Mn-Ni3Co alloys. The concentration dependences of R0, Rs, Bs, and ? were also studied in the ordered state of these alloys. It is concluded from an analysis of the experimental results that the decreases inR0 and ? during the ordering of Ni3Mn and as a result of the alloying of ordered Ni3Mn with slight amounts (~5 at. %) of iron are due primarily to a decrease in the hole contribution to transport and to a decrease in the state density in the 3d band of these alloys near the Fermi level. The experimental data are in satisfactory agreement with the curve calculated by Yamashita et al. [6] for the density of 3d states in ordered Ni3Mn and Ni3Fe alloys. 相似文献
3.
Exchange (or multiplet) splitting, ΔEs of the 3s core-level of Mn in RMn2Si2 (R = La to Nd, Sm and Gd) has been observed using XPS technique. The measured value of ΔEs is used to determine the magnetic moment on Mn ion in RMn2Si2. ΔEs has also been measured for the 4s and 5s levels of R in RMn2Si2 and it is found that the value of ΔEs increases with increase in the number of unpaired spins (La to Gd). 相似文献
4.
Investigation of slow surface states on a real germanium surface by the optical excitation technique
The slow states (SS) charging ΔQs under the action of light quanta of different energy (2 ? hv ? 4.6 eV) has been investigated on a real germanium surface. The considerable influence on the optical SS charging of the preparation method as well as of adsorption-desorption processes has been revealed. On the basis of the spectral dependencies ΔQs(hv) the conclusion has been made about the existence of the adsorption-sensitive system of “fluctuation” electron states near the edges of energy bands of the oxide layer. The photocharging method has been shown the construction of the whole energy scheme of the semiconductor-dielectric heterojunction (including the band gap of the dielectric layer). The possible origin of the deep traps in oxide layer which are responsible for the optical charging of a real germanium surface, has been discussed. 相似文献
5.
We have used low temperature (90?K) transmission electron microscopy to investigate the ‘charge ordering’ modulation in the mixed valent manganite, La1? x Ca x MnO3. It has been stated that Mn3+ and Mn4+ ions order at low temperature to produce a structural modulation composed of supercells whose size is an integer multiple of the unmodulated unit cell. Here, we use convergent beam electron diffraction to show that the periodicity of the modulation need not be an integer multiple of the undistorted cell, even on the smallest scales. We therefore suggest that this modulation is a charge density wave with a uniform periodicity. We show that the modulation wavevector lies close to the a* axis of the crystal but need not be exactly collinear. A typical grain of size 0.5?µm in La0.48Ca0.52MnO3 had a wavevector which varied on a scale of tens of nanometres with an average of ?q??=?0.450a * and a standard deviation Δq?=?0.004?a* in its magnitude and Δθ?=?0.56° in its direction at 90?K. The magnitude of the wavevector in this composition fell by 20% as the temperature was increased from 90?K to room temperature. This change occurred by nucleation and growth. Although weak, the modulation was still present at room temperature, some 30?K above the ‘charge ordering temperature’. 相似文献
6.
D.A. Doane 《Journal of magnetism and magnetic materials》1977,5(3):184-187
In this paper, we consider the single crystal analogue of the ΔE-effect in hexagonal materials with uniaxial magnetic anisotropy. We define Δsijld as the fractional change in the elastic compliance tensor sijkl in the demagnetized state relative to its value in the saturated state. The Δs-effect depends in general on the direction of the applied stress and the resulting magnetostrictive strain. We can show, however, that Δsijkl is always nonnegative when i=k and j=l. We then consider the measurements of the elastic constants in magnetic materials which have large magnetocrystalline anisotropy. The stresses applied in these measurements are not sufficient to rotate the magnetization away from the magnetically preferred direction, and hence cause no magnetostriction, and no Δs-effect. Therefore, it is not necessary to apply a saturating magnetic field along the easy axis in order to measure the true elastic constants in these materials. 相似文献
7.
Theoretical predictions on the effect of magnetic fields of variable strength on the rotational structure of doublet-quartet transitions in orthorhombic near symmetric top molecules are reported, with the assistance of computer simulations of line profiles. Low-field profiles are discussed, and it is shown that low-field linewidths are approximately equal to 2gβH|ΔJ ? ΔN| for transitions between states of any spin multiplicity. In a high field, transitions allowed by direct spin-orbit contamination of the combining states give rise to three lines with ΔMs = 0, ±1, whereas two additional lines, with ΔMs = ±2, are found if the combining states are appreciably contaminated also by indirect coupling to the active states, through intermediate levels. Computed Zeeman profiles are reported and discussed for several typical cases, with emphasis on the effects of different light polarizations. Prospectives of applicability are briefly outlined. 相似文献
8.
Selection rules on the rotational structure of doublet-quartet transitions in asymmetric top molecules are discussed on the basis of the spin-orbit coupling mechanism, rather than by symmetry arguments, and some additional rules are found with respect to a previous work. In the case that the combining doublet and quartet states are appreciably mixed only with levels directly connected to them by the spin-orbit operator, it turns out that, except for the very low values of the rotational quantum numbers, branches with |ΔN ? ΔJ| > 1 are essentially forbidden. Thus, branches with ΔN = ± 3 (T and N branches) are not expected to be observable. In this case, it is found also that in a high magnetic field transitions with ΔMs = ±2 are forbidden, and only ΔMs = 0, ±1 bands are expected to occur. All these restrictions are removed if the combining states are also appreciably contaminated by states indirectly connected to them by the spin-orbit operator, through intermediate levels. 相似文献
9.
We have generalised our earlier work calculating the induced density of states in alkali chemisorption to include the valence np level in addition to the s level. This allows the theory to take account of the possibility of sp hybridization. Hybridization is said to be weak is the sp level separation ΔEsP exceeds twice the width of the s or pz resonance. In the converse case hybridization is strong and the induced density of states no longer reflects distinguishable s and pz resonances. We argue that ΔEsP for the chemisorbed alkali exceeds considerably that for the free alkali atom. In the case of Na on rs = 2 jellium (considered typical of the smaller alkali on rs = 2?3 substrates) hybridization is strong for the atomic value of ΔEsp but weak when a somewhat larger value is taken, making the conclusions a little indefinite. For Cs on Cu(111), we find a clear situation of weak hybridization with the atomic ΔEsP and a fortiori with a more realistic value. There should thus be a well defined 6s resonance in this system. Our estimate of the width of the 6s resonance is in good agreement with photoemission data. 相似文献
10.
We solve a 2D model of N-component dense electron gas in the limit N→∞ and in the range of the Coulomb interaction parameter N ?3/2?r s ?1. The quasiparticle interaction on the Fermi circle vanishes as ?2/Nm. The ground-state energy and the effective mass are found as series in powers of r s 2/3 . In the quantum Hall state on the lowest Landau level at integer filling 1?ν<N, the charge-activation-energy gap and the exchange constant are Δ=log(r s N3/2)?ωH/ν and J=0.66?ωH/ν. 相似文献
11.
Yu. N. Uzikov 《Few-Body Systems》2008,44(1-4):211-213
Recent COSY results on the deuteron breakup reaction pd → {pp} s n with formation of the fast 1 S 0 pp pair in forward direction at beam energies 0.6–1.9?GeV are reviewed. A contribution of the three-body forces related to the Δ-isobar excitation is found to be dominant at 0.6–1?GeV. A high sensitivity of the pd → {pp} s n cross section to the short-range NN-interaction is emphasized. 相似文献
12.
M. A. Yurishchev 《Journal of Experimental and Theoretical Physics》2006,103(5):808-818
The coordinates of the critical points of spin-S Ising models with coupling constants J and J′ are calculated for 1/2 ≤ S ≤ 13/2. The calculations are performed for several values of S and Δ ≡ J′/J independently by using the phenomenological renormalization-group method or (approximate) self-duality. Numerical results combined with a mean-field analysis show that the critical coupling strength for Δ ~ 1 (weakly anisotropic lattice) is K c (S) (Δ) = K c (S) (1)[1 + a(1 ? Δ)], where a = (d ? 1)/d is independent of S (d is the space dimension). Both free energy and internal energy are determined at the critical points. An extremum of the critical internal energy is found at Δ* ∈ (0, 1). The parameter Δ* can be used as a criterion that separates quasi-isotropic and quasi-one-dimensional regimes (Δ* < Δ ≤ 1 and Δ < Δ*, respectively). The finite-size scaling amplitudes A s and A e of the inverse spin-spin and energy-energy correlation lengths are estimated. Calculations show that the amplitudes A s and A e are independent of S within the accuracy of the adopted approximations. Moreover, their ratio A e/A s is independent of the anisotropy parameter Δ. These results support the Ising universality hypothesis. 相似文献
13.
The ESR parameters of the cations Be+ 2, Mg+ 2, Ca+ 2, BeMg+, BeCa+, MgCa+ and the mixed radicals ZBe, ZMg, ZCa (Z = Li, Na, K), all having a X 2Σ+ u(1σ2 g1σu)/X 2Σ+(1σ22σ) ground state, have been studied theoretically. The A iso and A dip constants have been calculated with UHF, CISD, MP2, B3LYP, PW91PW91 wavefunctions, and 6–311+G(2df) basis sets. The electron spin g factors (magnetic moment μs) have been evaluated from correlated (MRDCI) wavefunctions, using a Hamiltonian based on Breit-Pauli theory with perturbation expansions up to second order, and 6–311 + G(2d) basis sets. As expected for s-rich radicals, the hyperfine spectra are governed by the A iso terms. Both Δg∥ and Δg⊥ values are negative, but Δg∥ lies close to zero. For Δg⊥, the coupling with 1 2Π(u) dominates the sum-over-states expansions. Although the singly occupied MOs (SOMO) are mostly of s character, the |Δg⊥| are relatively large, up to 5200 ppm for cationic, and up to 7850 ppm for neutral radicals. These large values are caused by low excitation energies and high magnetic transition moments, the latter due to the fact that the σ?(s-s) SOMO has the same nodal properties as a pσ orbital. Of the radicals considered here, an ESR spectrum is available only for Mg+ 2. Our theoretical A iso of ?287 MHz reproduces well the matrix result (-291 MHz). Calculated values of ?10 ppm for Δg∥ and of ?1280 ppm for Δg⊥ give an average 〈Δg〉 = ?860 ppm that lies within the experimental range of ?600(±300) ppm in Ne, and of ?1300(±500) ppm in Ar matrices. 相似文献
14.
A generalized Weyl—Wigner quantization scheme unifying P-Q and Q-P ordering and Weyl ordering of operators
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By extending the usual Wigner operator to the s-parameterized one as 1/4π2 integral (dyduexp [iu(q-Q)+iy(p-P)+is/2yu]) from n=- ∞ to ∞ with s beng a,real parameter,we propose a generalized Weyl quantization scheme which accompanies a new generalized s-parameterized ordering rule.This rule recovers P-Q ordering,Q-P ordering,and Weyl ordering of operators in s = 1,1,0 respectively.Hence it differs from the Cahill-Glaubers’ ordering rule which unifies normal ordering,antinormal ordering,and Weyl ordering.We also show that in this scheme the s-parameter plays the role of correlation between two quadratures Q and P.The formula that can rearrange a given operator into its new s-parameterized ordering is presented. 相似文献
15.
A band contour analysis is carried out for the ν3 absorption in SF6. Values of ΔB = ? (1.0 ? 1.5) × 10?4cm?1, ζ3 = 0.701, and ν0 = 948.2cm?1 are found. Tentative assignments are given for the SF6 rotational states which are pumped by the P(14) through P(22) lines of the CO2 laser. 相似文献
16.
The phase diagrams of the three-layer Ising model on the honeycomb lattice with a diluted surface have been constructed using the probabilistic cellular automata based on Glauber algorithm. The effects of the exchange interactions on the phase diagrams have been investigated. A general mathematical expression for the critical temperature is obtained in terms of relative coupling r = J1/J and Δs = (Js/J) ? 1, where J and Js represent the nearest neighbor coupling within inner- and surface-layers, respectively, and each magnetic site in the surface-layer is coupled with the nearest neighbor site in the inner-layer via the exchange coupling J1. In the case of antiferromagnetic coupling between surface-layer and inner-layer, system reveals many interesting phenomena, such as the possibility of existence of compensation line before the critical temperature. 相似文献
17.
The low-temperature specific heat, magnetic susceptibility, and thermal expansion are studied experimentally in the fcc boride HoB66 and compared to similar quantities in non-magnetic LuB66. The anomalous behaviour observed in HoB66 is explained within a glass-like picture together with magnetic subsystem ordering processes. The character of the observed anomalies suggests the existence of a spin-glass phase transition in HoB66 below a characteristic temperature of T s ?≈?0.98?K. 相似文献
18.
S. S. Aplesnin L. I. Ryabinkina O. B. Romanova D. A. Velikanov A. D. Balaev D. A. Balaev K. I. Yanushkevich A. I. Galyas O. F. Demidenko O. N. Bandurina 《Journal of Experimental and Theoretical Physics》2008,106(4):765-772
We have studied the resistivity and thermoelectromotive force (thermo emf) in a temperature range of T = 80–1000 K, the magnetic susceptibility and magnetization in a temperature range of T = 4.2–300 K at an external magnetic field of up to 70 kOe, and the structural characteristics of Co x Mn1?x S sulfides (0 ≤ x ≤ 0.4). Anomalies in the transport properties of these compounds have been found in the temperature intervals ΔT 1 = 200–270 K and ΔT 2 = 530–670 K and at T 3 ~ T N. The temperature dependences of the magnetic susceptibility, magnetization, and resistivity, as well as the current-voltage characteristics, exhibit hysteresis. In the domain of magnetic ordering at temperatures below the Néel temperature (T N), the antiferromagnetic Co x Mn1?x S sulfides possess a spontaneous magnetic moment that is explained using a model of the orbital ordering of electrons in the t 2g bands. The influence of the cobalt-ion-induced charge ordering on the transport and magnetic properties of sulfides has been studied. The calculated values of the temperatures corresponding to the maxima of charge susceptibility, which are related to a competition between the on-site Coulomb interaction of holes in various subbands and their weak hybridization, agree well with the experimental data. 相似文献
19.
G.A. Somorjai 《Surface science》1973,34(1):156-176
Low energy electron diffraction (LEED) studies of the structure of adsorbed molecules on crystal surfaces revealed that ordered surface structures predominate under most conditions of the experiments. In the absence of chemical reactions with the substrate, the degree of ordering depends on the heats of adsorption, ΔHads, and the activation energies for surface diffusion, ΔED1. Since ΔHads is usually markedly larger than ΔED1, small changes of substrate temperature facilitate ordering without appreciable increase in desorption rates. The surface structures of adsorbed gases that have been reported so far have been tabulated. For molecules whose size is compatible with the interatomic distance of the substrate, rules of ordering can be proposed that permit prediction of the structure of the adsorbed layer that is likely to form. These rules indicate close packing due to attractive interactions in the adsorbed layer, and that the rotational multiplicity of the substrate is likely to be maintained by the adsorbate structure. When molecules whose dimensions are larger than the substrate interatomic distance are adsorbed, the conditions that control ordering are more complex and simple rules may not be readily applicable.The surface structures of adsorbed gases have also been studied on high Miller Index substrate surfaces. These surfaces are characterized by ordered steps separated by terraces of low index surface orientation. Many gases have different ordering characteristics on stepped surfaces than on low index crystal faces due to the stronger substrate-adsorbate interactions in these surfaces. The dissociation of diatomic molecules at steps induces the formation of new types of surface structures (frequently one-dimensional) and the dehydrogenation of hydrocarbons at steps induces the formation of ordered carbonaceous surface structures that would not nucleate on low index substrate planes.So far, mostly work function changes upon adsorption gave indication of the magnitude of charge transfer upon adsorption and on forming of new surface chemical bonds. Most recently, chemical shifts of the Auger transitions of the substrate atoms and of the adsorbed molecules upon chemisorption, have been found to provide additional information on charge redistribution during adsorption. 相似文献
20.
Using interband spectroscopy we have systematically investigated the one-dimensional energy gaps that occur in the electron inversion layer band structure on surfaces of Si tilted by angle θ from (001). While the positions of the gaps are in good agreement with the valley-splitting model by Sham et al., we observe dependences of the size ΔE0 of the lowest gap on electron density Ns, θ and azimuthal angle φ that deviate from theoretical predictions. The observed nonlinear Ns-dependence of ΔE0 is interpreted as a ky-dependence. 相似文献