Interfacial segregation in Ag-Au,Au-Pd,and Cu-Ni alloys: I. (100) surfaces

Atomistic simulations of segregation to (100) free surface in Ag–Au, Au–Pd, and Cu–Ni alloy systems have been performed for a wide range of temperatures and compositions within the solid solution region of these alloy phase diagrams. In addition to the surface segregation profiles, surface free energies, enthalpies, and entropies were determined. These simulations were performed within the framework of the free energy simulation method, in which an approximate free energy functional is minimized with respect to atomic coordinates and atomic site occupation. The effects of the relaxation with respect to either the atomic positions or the atomic concentrations are discussed. For all alloy bulk compositions (0.05 C 0.95) and temperatures (400 T(K) 1,100) examined, Ag, Au, and Cu segregates to the surface in the Ag–Au, Au–Pd, and Cu–Ni alloy systems, respectively. The present results are compared with several theories for segregation. The resultant segregation profiles in Au–Pd and Ag–Au alloys are shown to be in good agreement with an empirical segregation theory, while in Cu–Ni alloys the disagreement in Ni-rich alloys is substantial. The width of the segregation profile is limited to approximately three to four atomic planes. The surface thermodynamic properties depend sensitively on the magnitude of the surface segregation, and some of them are shown to vary linearly with the magnitude of the surface segregation.     

Effect of s-d hybridization in residual resistance of binary ordered alloys

Calculations are made of the residual resistance of the ordered binary alloys stemming from the difference between the d levels of the components. The residual resistance is found to be dependent on the degree of the long-range order. It is established that in alloys in which the Fermi energy E_F is far from the d resonances decreases monotonically as increases. When E_F approaches one of the resonance levels the resistance increases severalfold and varies monotonically with . The results are used in interpreting the anomalies of the temperature dependence of the resistance of iron-palladium alloys.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 39–44, April, 1979.The author is indebted to A. A. Kuranov and P. N. Syutkin for providing us with detailed experimental data, and to S. I. Masharov for his fruitful discussion.     

Levinson's Theorem for the Schrödinger Equation in One Dimension

Levinson's theorem for the one-dimensional Schrödinger equation with asymmetric potential which decays at infinity faster thanx ^–2 is established by theSturm-Liouville theorem. The critical case where the Schrödinger equation hasa finite zero-energy solution is also analyzed. It is demonstrated that the numberof bound states with even (odd) parityn ₊(n _–) is related to the phase shift ₊ (0)[_– (0)] of the scattering states with the same parity at zero momentum as ₊ (0)+ /2 =n ₊ and _– (0) =n _– for the noncritical case, and ₊ (0) =n ₊ and_– (0) – /2 =n _– for the critical case.     

Determination of the Order Parameter in Binary Fluid Mixtures

We propose a microscopic approach to the study of phase transitions in fluid mixtures. It is based on the collective variables method with a reference system. The problem of definition of the order parameter in a two-component fluid system is considered in detail. This system is described with two sets of collective variables: _k and _k. It is shown that the CV connected with the order parameter is _k=0 in the case of a gas–liquid critical point as well as in the case of a mixing–demixing phase transition. The relations between the microscopic parameters, temperature, density and concentration which determine the particular form of ₀ for each of these phenomena are obtained. Based on these results we will be able to construct an effective Ginsburg–Landau–Wilson Hamiltonian.     

TDPAC studies of internal AgIn alloy oxidation

The internal oxidation of dilute AgIn alloys in open air versus In concentration and oxidation temperature was investigated by the TDPAC technique. The¹¹¹In interaction described by the broad quadrupole frequencies distribution aroundv _Q = 115 MHz and =0.5–0.7 was observed and interpreted as due to nonstoichiometric In–O_X cluster formation. For higher temperatures and more concentrated alloys additionally quasiunique frequencyv _Q 157 MHz with 0.28 was evidenced and ascribed to¹¹¹In interaction inside In₂O₃ precipitates. The internal oxidation under reduced oxygen pressures was studied and the thermal stability of the complex formed was tested. The effect of surface preparation on internal oxidation was observed.     

Interfacial segregation in Ag-Au,Au-Pd,and Cu-Ni alloys: II. [001] Σ5 twist grain boundaries

Atomistic simulations of segregation to [001] 5 twist boundaries in Cu–Ni, Au–Pd, and Ag–Au alloy systems have been performed for a wide range of temperatures and compositions within the solid solution region of these alloy phase diagrams. In addition to the grain boundary segregation profiles, grain boundary free energies, enthalpies, and entropies were determined. These simulations were performed within the framework of the free energy simulation method, in which an approximate free energy functional is minimized with respect to atomic coordinates and atomic site occupation. For all alloy bulk compositions (0.05 C 0.95) and temperatures (400 T (K) 1,100) examined, Cu and Au segregates to the boundary in the Cu–Ni and Au–Pd alloy systems, respectively; although in the Ag–Au alloys, the majority element segregates to the boundary. The width of the segregation profile is limited to approximately three to four (002) atomic planes. The classical theories for the segregation, and the effects of the relaxation with respect to either the atomic positions or the atomic concentrations, are discussed. The boundary thermodynamic properties depend sensitively on the magnitude of the boundary segregation, and some of them are shown to vary linearly with the magnitude of the grain boundary segregation.     

Investigations of the excitation energy transport mechanism in donor-acceptor systems

Measurements of fluorescence quantum yield _D/_oD of Na-fluorescein (donor; D) versus concentration of rhodamine B (acceptor; A) in viscous solutions have been carried out. The donor concentration in these solutions was as follows:C _D=2·10^–2 M (system I), 1.5·10^–2 M (II), 10^–2 M (III), 3·10^–3 M (IV), and 5·10^–5 M (V). The experimental results have been compared with current theories of nonradiative electronic energy transfer (NEET). In the case of very strong migration (systems I, II, and III), a significant influence of correlations (between configurations of D and A molecules in the surroundings of successively excited donors) on quantum yield _D/_oD has been determined. Experimental values have been found to be clearly higher in comparison with those predicted theoretically. The influence of possible factors on the decrease in the effectiveness of excitation energy transport to traps-acceptors in systems of very strong migration has been discussed.Dedicated to Professor A. Kawski on the occasion of his 65th birthday.     

Phenomenological rules for the computation of magneto-electric susceptibilities

Applying the model of the anharmonic oscillator, phenomenological expressions were derived, allowing calculation of the components of tensors describing non-linear magneto-electric susceptibilities. Detailed calculations were carried out for the pseudo-tensor of fourth order ^eeem in terms of which magneto-optical birefringence and rotation are expressed for the monocrystals KDP, DKDP, ADP, KDA, LiNbO₃, LiTaO₃ and NaClO₃. From the results obtained it follows that non-linear magneto-electric susceptibilities, which are described by the pseudo-tensor ^eeem are of the order of 10^–16 m V^–1T^–1.Part of this work was carried out under Research Project MR 15.     

Pseudopotential calculation of the energy of vacancy formation in binary alloys as a function of the degree of far order

Pseudopotential theory is used to study the dependence of energy of vacancy formation E_IV ^f in binary replacement alloys as a function of the degree of far order is shown that E _IV ^f =E_o+E·]², where E_o is the energy of vacancy formation in a disordered alloy, E then contains the ordering energy. It is shown with examples of the alloys CuZn, AuZn, and AgCd that the energy of vacancy formation can decrease with increase in the degree of far order. It is found that in calculating the vacancy formation energy it is necessary to consider lattice relaxation energy, since such consideration can lead to a change in the sign of E.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 62–67, June, 1984.     

On the directional dependence of composite field operators

The Wilson expansion of the field operator productA ₁(x ₁)A ₂(x ₂) may be used to define composite operators which are local with respect to 1/2(x ₁+x ₂) and depend in addition on a vector proportional to the distancex ₁–x ₂. It is proved that the composite operators are polynomials in , for fixed ² 0, and that their dependence on ² only involves powers of ² and lg².This work was supported in part by the National Science Foundation Grant No. GP-25609.     

Kinetics of small perturbations in an isotropic world

Long-wavelength gravitational perturbations are studied in an isotropic expanding universe filled with an ultrarelativistic gas. A kinetic study in the collisionless approximation shows that scalar and vector perturbations which appear at a time ₀ 1/n, where N is the wave vector and is the time coordinate x⁴, grow if the perturbation of the macroscopic momentum density of the gas at time ₀ is nonvanishing. The growth continues until the time ₁=27₀, at which the perturbation of the macroscopic momentum density of the gas vanishes. A solution is also derived for tensor perturbations in the limit n 1.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 37–45, April, 1978.     

Spectral characteristics for a fiber grating external cavity laser

A numerical investigation has been carried out on the influence of the antireflection (AR) coating of laser, the coupling efficiency of laser and fiber (), and the reflectivity of fiber grating (R _g) on the side-mode suppression ratio (SMSR) of the fiber grating external cavity laser (FGECL). The FGECL was fabricated by the assembly of the multimode Fabry–Perot (FP) laser chip and fiber grating. The results showed that the FGECL with a lower AR coating, higher and R _g exhibited a better SMSR. A comparison of the SMSR dependence on the and R _g showed that SMSR increased more rapidly with increasing than SMSR for R _g. These spectral characteristic studies of the SMSR dependence on the device parameters of the AR coating, , and R _g may provide useful device designs for the practical fabrication of a FGECL for use in dense wavelength division multiplexing (DWDM) applications.     

Light transformers with photon multiplication

Conclusions Crystal phosphors with photon multiplication in the optical range can be used as efficient light transformers. Their use in mercury-free luminescent gas-discharge lamps is especially promising. Analysis of the present position as regards neon discharges indicates that by using phosphors with _t=2–3 it might be possible to create light sources with an efficiency of 30–50 1m/W which would operate solely under outdoor lighting conditions. Evaluation of the prospects of developing light transformers with _t=2–3 indicates that this problem is solvable in principle.We are grateful to the staff of the Ionic Crystal Physics Sector of the Institute of Physics and Astronomy, AS Estonian SSR, and especially to G. Liid'ya, R. Kink, N. Lushchik, I. Meriloo, N. Rooze, and R. Milenina for taking part in our discussions of the problem of transformers with photon multiplication. We also wish to thank V. V. Fedorov and F. A. Butaeva of the All-Union Scientific Institute of Lighting Engineering, who drew our attention to the importance of developing luminophors with>1 for new light sources.Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 10, No. 1, pp. 127–133, January, 1969.     

Atomic ordering in ternary alloys with hexagonal-close-packed structures. II

This paper constitutes a theoretical study of the influence of interstitial impurity atoms on the type of order-disorder transition in an alloy of the AB₃-C_in type with an hcp structure. Allowance is made for a variety of types of interstices over the range 0 1. The free energy is calculated by the Gorskii-Bragg-Williams method. In the presence of an impurity there may be a change in the magnitude of the jump taking place in the degree of long-range order at the transition point, and also a change in the type of order-disorder transition occurring.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 20–26, March, 1974.     

On the possibilities to study the exotic state 1−+ in photoproduction of the πη, πη′ systems

We show that photoproduction experiments provide propitious conditions to study the exotic state 1^–+ in the and channels. For unpolarized photons contributions from natural and unnatural parity exchanges do not interfere with each other, a fact which permits to estimate the correctness of phase shift analyses. In photoproduction of the ⁺ system in the mass range ofa ₂(1320) a more stringent limit on the product (1^–+)Br(1^–+) can be obtained than in experiments on Primakoff production on nuclei. Particularly favourable is the study of the state 1^–+ in the coherent photoproduction of the ⁰ and ⁰ systems on nuclei, with significantly enlarged statistics and a simplified phase shift analysis.     

Integrability conditions for Killing spinors

The conditions for the existence of solutions ofD _µ=±c_µ are discussed. In general, it is not sufficient to consider only the first integrability condition [D _µ,D _v ]=–2c ²_{µv}; in particular, the second integrability condition is needed to explain why, in certain cases, only for one choice of sign does a solution exist. The Killing spinor-tensors, as defined by Walker and Penrose, are shown to be the spinorial equivalent of conformal Killing tensors. Their relationship to the Killing spinors and spinor-vectors used in supergravity, is given.On leave from the Institute for Theoretical Physics of the State University of New York at Stony BrookWork supported in part by the U.S. Department of Energy under Contract No. DEAC-03-81-ER 40050 and Weingart Fellowship     

Relativistic effects in decay of S-wave quarkoniums

The width of S-wave quarkonium decays (_c, _b ; and J/, Y e⁺e^–) are calculated using the quasipotential approach. The nontrivial dependence of decay amplitude on relative quark momentum is considered. It is shown that relativistic corrections reach values of 30–50% in the processes studied.Samara State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 46–53, May, 1995.     

Production of an electron-positron pair and a photon from the vacuum in a radiation-dominated universe

A study is made of the production of an electron-positron pair and a photon from the vacuum in a Robertson-Walker space with metric ds²=a²()(d²–dx²–dy²–dx²). In Minkowski space, this process is forbidden by the conservation laws. The differential probability of the process is calculated, and its behavior in various kinematic regions is investigated. The probability of the process is estimated numerically for times close to the electron Compton time, and the probability of production of a pair and photon from the vacuum is compared with the probability of pair production in the absence of radiative coupling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 61–66, February, 1991.     

Intrinsic point defects in niobium: Trapping at100Pd and111In impurities observed by PAC

Radiation-induced lattice defects in high-purity niobium have been investigated in the temperature range of 30K to 540 K by means of - perturbed angular correlation (PAC) measurements using the radioactive probes¹⁰⁰Pd/¹⁰⁰Rh and¹¹¹In/¹¹¹Cd. Both probes were produced within the niobium samples by means of heavy-ion nuclear reactions. At the Pd impurities trapping of defects occurred during heavy-ion irradiation at about 30 K in two defined configurations: defect 1(Pd) withv _Q1=e ² qQ/h=42(±2) MHz, ₁=0 and defect 2 (Pd) withv _Q2=(±2) MHz, ₂=1. Two defects were observed at the In impurities in annealing stage III (around 250 K) after heavy-ion as well as electron irradiations: defect 1(In) withv _Q1=87(±1) MHz, ₁=0 and defect 2(In) withv _Q2=105(±2) MHz, ₂=0.65(±0.02). A third defect (defect 3(In):v _Q3=177(±2) MHz, ₃0.2) appeared above 260 K after heavy-ion irradiation only. The data are interpreted in terms of interstitial trapping at the Pd impurities and vacancy trapping at the In impurities. Information on the microscopic structure of defect 1(In) and 2(In) is obtained from a PAC-single-crystal experiment. For defect 1(In) axial 111-symmetry is found, which leads us to identify this defect with a monovacancy as nearest neighbor with respect to the In probe. Defect 2(In) is the trapped divacancy for which an orientation is found that is consistent with both vacancies being nearest neighbor to the probe but second nearest neighbors to each other.     

NMR enhancement and NMR relaxation in a <110> FeSi Néel-type single crystal

⁵⁷Fe NMR measurements with a Néel-type single crystal are described. The behaviour of the magnetic structure was calculated as function of the internal fieldH _i. A clear distinction between wall and domain signals could be made. The corresponding relative enhancement factors _w ^r (H _i) and _D ^r (H _i) have been calculated and are in agreement with the measurements. The relaxation in the 90° Bloch walls is pure exponential. Both ratesT ₁ ^–1 andT ₂ ^–1 are proportional to _w ² (H _i). The measurements make proof, that the 90° walls are folded inside the crystal.K.-H. König and H. Brömer, Verhandl. DPG(VI)22, I, AM-14.11 (1987)