Internal friction in alloys due to plasticity of the diffusion phase transformation

An analytic expression is obtained for the time dependence Q ^?1(t) of internal friction associated with plasticity of a phase transformation. Time dependences Q ^?1(t) of internal friction of the Pb-62Sn and Pb-1.9Sn alloys (wt.%) alloys were studied in the regime of continuous excitation of resonant flexural vibrations. The measurements of the Q ^?1(t) dependences for 1 h at room temperature and a fixed strain amplitude ε₀ ≈ 7 and 19 min) for the Pb-62Sn alloy. For the Pb-1.9Sn alloy under the same conditions, an exponential decrease followed by an internal friction peak (at t _m ≈ 7 min) is observed. It is shown numerically that the above singularities of internal friction are formed by processes of intermittent phase decomposition of Pb-Sn alloys in the cyclic stress field produced by an external load. Experimental data on Q ^?1(t) are used for reconstructing the kinetic curves describing the decomposition (conversion) ratio as a function of time and for calculating the corresponding values of parameters K and n of the Avrami kinetic equation for the Pb-62Sn alloy.     

Internal friction of Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> single crystals

This paper reports on the results of measurements of the internal friction Q^?1 and the shear modulus G of Li₂B₄O₇ single crystals along the crystallographic directions [100] and [001] in the temperature range 300–550 K for strain amplitudes of (2–10)×10^?5 at infralow frequencies. The anomalies observed in Q^?1 and G in the temperature range 390–410 K are due to thermal activation of the mobility of lithium cations and their migration from one energetically equivalent position to another. A jump in the internal friction background is revealed in the vicinity of the Q^?1 and G anomalies for the Li₂B₄O₇ crystal. The magnitude of this jump depends on the crystallographic direction.     

Structure and dielectric response of (1–<Emphasis Type="Italic">x</Emphasis>)NaNO<Subscript>2</Subscript> + <Emphasis Type="Italic">x</Emphasis>BaTiO<Subscript>3</Subscript> composites at <Emphasis Type="Italic">x</Emphasis> = 0.05 and 0.1

The (1–x)NaNO₂ + xBaTiO₃ composites of two compositions (x = 0.05 and 0.1) have been studied by powder neutron diffraction and broadband dielectric spectroscopy (frequency region 10^–1–10⁷ Hz). The temperature dependences of the ferroelectric order parameter of NaNO₂ in the composites and pure NaNO₂ have been measured. The frequency dependences of the real and imaginary parts of the permittivities of the composites and pure NaNO₂ have been analyzed in the temperature range 25–187°C. The anomaly of the dielectric response observed at T ~ 147°C is assumed to be related to the processes of accumulation and “resolution” of charges at the BaTiO₃ particle boundaries.     

Die relativen Quadrupolmomente der ersten angeregten 2+-Zustände von Os188, Os190 und Os192

The angular distributions of the deexitationγ-rays following Coulomb-excitation of the first excited 2⁺-states in Os¹⁸⁸, Os¹⁹⁰ and Os¹⁹² were measured using a metallic Target of natural Osmium. The measured attenuation coefficients areG ₂(Os¹⁸⁸)=0.798±0.013,G ₂(Os¹⁹⁰)=0.917±0.030 andG ₂(Os¹⁹²)=0.940±0.030. As a general test the angular distribution of the 330 keV-γ-rays of Pt¹⁹⁴ was also measured. This distribution was found to be completely undisturbed. Assuming pure electric quadrupole interaction with the internal crystalline fields one obtains an interaction frequency ofΔv _Q =eQ V _zz /h=278±32 MHz for the 155 keV-state of Os¹⁸⁸. Because the electric field gradients acting on the decaying nucleus are the same for all isotopes, one can deduce the ratio of the quadrupole moments of the excited states. The result isQ(Os¹⁸⁸)∶Q(Os¹⁹⁰)=1.11 _?0.19 ^+0.28 andQ(Os¹⁹⁰)∶Q(Os¹⁹²)=1.03±0.30. The effects of the uncertainties in the effective field gradients and their possible asymmetries on the integral attenuation factors are discussed. For 1≧G ₂?0.75 these effects are found to be small.     

Study of photon electroproduction on the nucleon at high and low energy by Virtual Compton Scattering

Virtual Compton Scattering (VCS) and Deeply Virtual Compton Scattering (DVCS) on the nucleon are two processes accessed via the photon electroproduction reaction (eN → eγN). In the first part of this paper we are interested by the DVCS on the neutron. We measured the (D(e, eγ)X-H(e, e'γ)X) unpolarized cross section and we extracted, for the first time, a non-zero contribution of (neutron-DVCS + coherent- deuteron-DVCS) at Q ² = 1.75 GeV² and x _B = 36 from Jefferson Lab experiment E08-025. VCS on the proton has been studied at Mainz Microtron MAMI at the four-momentum transfer squared Q ² = 0.5 GeV², below the pion production threshold. In the second part of this paper we present our preliminary results of the structure functions (P _LL ? (P _TT/ε)) and P _LT, and the electric and magnetic generalized polarizabilities α _E (Q ²) and β _M (Q ²) extracted from this experiment.     

Effect of gamma irradiation on internal friction in lithium tetraborate

The effect of gamma irradiation on the mechanical properties of lithium tetraborate Li₂B₄O₇ in the single-crystal and vitreous states is investigated. It is found that, after irradiation of the Li₂B₄O₇ single crystal, the temperature range of the dissipative process initially occurring at 380–420 K becomes broader and the fine structure of the peak in the temperature dependence of the internal friction Q^?1(T) undergoes a substantial trans-formation. After irradiation of the vitreous Li₂B₄O₇ sample, the increase in the internal friction, which is characteristic of the onset of the α relaxation in this material, is not observed in the dependence Q^?1(T) up to a temperature of 570 K. It is shown that the mechanical properties of the irradiated samples are almost completely recovered after annealing at 570 K for 1 h.     

Hall-Petch analysis for temperature and strain rate dependent deformation of polycrystalline lead

A dislocation pile-up analysis of the Hall-Petch constant k _ε for the tensile deformation of polycrystalline lead over a wide range of temperature T and at two strain rates has been made. The predicted and experimental Hall-Petch dependencies k _ε ² = f (T) are in good agreement. Lower than predicted k _ε values at very low temperatures are attributed to the high curvature of grain boundaries which experience high localized plasticity and consequent shear banding.     

Dielectric relaxations,magnetodielectric and magnetoelectric interactions in Bi0.6La0.4MnO3 ceramics

Complex permittivity ε*/ε₀ = ε′/ε₀–iε″/ε₀ of the bismuth–lanthanum manganite Bi_0.6La_0.4MnO₃ ceramics has been measured in the temperature range of 10–220 K at frequencies f = 20–10⁶ Hz and magnetic inductions B = 0–0.846 T. At a temperature of 80 K, the spectra ε′/ε₀(t) and ε″/ε₀(t) demonstrate the dielectric relaxation that is a superposition of contributions of several relaxation processes, each of which is dominant in its frequency range: I (f < 10³ Hz, II (10³ < f < 10⁵ Hz), and III (10⁵ < f < 10⁶ Hz). In the range of 10–120 K, anomalous behavior of ε′/ε₀(T) and ε″/ε₀(T) is observed near the temperature of the transition from the paramagnetic to ferromagnetic phase and is due to the Anderson localization of charge carrier on a spin disorder.     

Ion ordering and ferroelectricity in Pb(<Emphasis Type="Italic">B</Emphasis>′<Subscript>0.5</Subscript><Emphasis Type="Italic">B</Emphasis>″<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> perovskites

The Pb(B′_0.5 B″_0.5)O₃ ferroelectric with a perovskite structure and the antiferroelectric of the same composition are usually considered to be the same compound regardless of whether the B′ and B″ ions in the octahedral positions are ordered even though they differ substantially in behavior. It is established that ion ordering can also occur in PZT-type solid solutions of the composition Pb(B′_x B″_{1 ? x} )O₃ with x ≈ 0.5. The mechanism of the influence of ion ordering on the behavior of crystals of both complex perovskites and PZT-type ceramics is discussed.     

Structure,Ferroelectric, and Magnetoelectric Properties of Bulk PZT–NiFe<Subscript>1.9</Subscript>Co<Subscript>0.02</Subscript>О<Subscript>4 – δ</Subscript> Composites

The phase composition, microstructure, and dielectric, ferroelectric, magnetic, and magnetoelectric properties of bulk ceramic (1 – x)PZT–xNiFe_1.9Co_0.02О_{4 – δ} composites with 3–0 connectivity have been studied. Using X-ray diffraction and electron microscopy, it has been established that the ferrimagnetic (spinel- like) and ferroelectric (tetragonal perovskite-like) phases separately exist in the composites of all compositions. The simultaneous existence of ferroelectric and ferrimagnetic properties in the composites is confirmed by measuring their P(E) and σ(B) hysteresis loops and studying the temperature dependences of dielectric and magnetic properties. The synthesized composites have high magnetoelectric characteristics: their voltage coefficient at x = 0.4 is 215 mV/A at a frequency of 1 kHz and 130 V/A at an electromechanical resonance frequency of 380 kHz.     

Raman scattering in sodium nitrite crystals near the phase transition

Optical Raman spectra of a ferroelectric sodium nitrite crystal have been detected in a wide spectrum range at various temperatures, including the region of the ferroelectric phase transition. A manifestation of a transverse soft polar mode of the A ₁(z) type responsible for the ferroelectric phase transition has been discovered in the spectrum at room temperature. This mode has been found to become overdamped even far from the ferroelectric phase transition temperature. This mode also appears as a central peak under heating. It has been found that the pseudoscalar mode of the A ₂ type has the highest intensity in the Raman spectrum of sodium nitrite. The frequency corresponding to the maximum intensity of this mode in the Raman spectrum varies from 130 cm^–1 at 123 K to 106 cm^–1 at T = 513 K. A fair agreement of the experimental data for the A ₁(z) mode with the Lyddane–Sachs–Teller relation has been established. The polariton curves for the A ₁(z) polar mode and the dispersion curves for axinons has been plotted.     

Structural phase transition in (1−<Emphasis Type="Italic">x</Emphasis>)SrTiO<Subscript>3</Subscript>+<Emphasis Type="Italic">x</Emphasis>SrMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> solid solutions

The temperature dependences of the shear modulus and internal friction in ceramic samples of (1?x)SrTiO₃+xSrMg_1/3Nb_2/3O₃ solid solutions were studied by the torsional vibration method in the range 80–300 K. It was established that the temperature T _a of the O _h ¹ -D _4h ¹⁸ structural phase transition in these solid solutions increases with increasing x, although the lattice constant also increases. A discussion is presented of the contributions to the T _a (x) dependence due to a change in the volume and changes caused by the presence of a second solid-solution component (the impurity contribution). It is also shown that the defect-induced relaxation revealed earlier in a study of the dielectric properties of these materials manifests itself in internal friction peaks.     

Singular Resonance in Fluctuation-Induced Electromagnetic Phenomena at the Rotation of a Nanoparticle near the Surface of a Condensed Medium

It has been shown that the rotation of a spherical nanoparticle with the radius R near the surface of a semi-infinite homogeneous medium can result in singular resonance in fluctuation-induced electromagnetic phenomena (Casimir force, Casimir friction, and radiative heat generation). Fluctuation electromagnetic effects increase strongly near this resonance even in the presence of dissipation in the system. The resonance occurs at distances of the particle from the surface d < d₀R(3/4ε″₁(ω₁)ε″₂ (ω₂))^1/3 (where ε″_i(ω_i) is the imaginary part of the dielectric function of the particle or the medium at the frequency of a surface phonon or plasmon polariton ω_i), when the rotation frequency coincides with poles in the photon generation rate at Ω ≈ ω₁ + ω₂. These poles are due to the multiple scattering of electromagnetic waves between the particle and surface under conditions of the anomalous Doppler effect. These poles exist even in the presence of dissipation. At d < d₀, depending on the particle rotation frequency, the Casimir force can change sign; i.e., the attraction of the particle to the surface changes to repulsion. The results can be important for the development of experimental methods for the detection of quantum friction.     

Thermophysical study of structural phase transitions in Na<Subscript>0.95</Subscript>Li<Subscript>0.05</Subscript>NbO<Subscript>3</Subscript> solid solution

Temperature dependences of specific heat C_p(T) and coefficient of thermal expansion ;(T) for Na_0.95Li_0.05NbO₃ sodium-lithium niobate ceramic samples are investigated in the temperature range of 100–800 K. The C_p(T) and α(T) anomalies at T₃ = 310 ± 3 K, T₂ = 630 ± 8 K, and T₁ = 710 ± 10 K are observed, which correspond to the sequence of phase transitions N ? Q ? S(R) ? T2(S). The effect of heat treatment of the samples on the sequence of structural distortions was established. It is demonstrated that annealing of the samples at 603 K leads to splitting of the anomaly corresponding to the phase transition Q → R/S in two anomalies. After sample heating to 800 K, the only anomaly is observed in both the C_p(T) and ;(T) dependence. Possible mechanisms of the observed phenomena are discussed.     

Das Kernquadrupolmoment des Mn55

With a recording photoelectric Fabry-Perot spectrometer and an atomic-beam light source the hyperfine structure of the Mn I-resonance linesλ=4031 Å,λ=4033 Å,λ=4034 Å (3d ⁵4s ² a ⁶ S _5/2?3d ⁵4s4p z ⁶ P _7/2,5/2,3/2 ⁰)and of the inter-combination linesλ=5395 Å andλ=5433 Å (3d ⁵4s ² a ⁶ S _5/2?3d ⁵4s4p z ⁸ P _7/2,5/2 ⁰) was measured. Furthermore the resonance lines have been measured with a pulsed atomic-beam in absorption. In this case the quotient (I ₀(ν)?I(ν))/I ₀(ν) was recorded, whereI(ν)=I ₀(ν) exp(?α(ν)d) is the observed intensity with absorption andI ₀(ν) the intensity of the light source. From the hyperfine structure splitting the value of the electric quadrupole moment of Mn⁵⁵ was derived to be:Q(Mn⁵⁵)=+(0.35±0.05)·10^?24 cm².     

Control of the perturbation-wave-vector range of modulation instability of dispersive electromagnetic waves in the nonlocal Josephson electrodynamics of a thin superconducting film

Modulation instability of dispersive electromagnetic waves propagating through a Josephson junction in a thin superconducting film is investigated in the framework of the nonlocal Josephson electrodynamics. A dispersion relation is found for the time increment of small perturbations of the amplitude. For dispersive waves, it is first established that spatial nonlocality suppresses the modulation instability in the range of perturbation wave vectors 0≤Q≤Q_B1(k), i.e., in the long-wavelength range of experimental interest. The modulation instability range Q_B1(k)<Q<Q_B2(k, A, L) can be controlled (which is a unique possibility) by varying a dispersion parameter, namely, the wave vector k [or the frequency ω(k)] of linear-approximation waves. In the wave-vector ranges 0≤Q≤Q_B1(k) and Q≤Q_B2(k, A, L), waves are shown to be stable.     

Limit of Fluctuations of Solutions of Wigner Equation

We consider fluctuations of the solution W _ε (t, x, k) of the Wigner equation which describes energy evolution of a solution of the Schrödinger equation with a random white noise in time potential. The expectation of W _ε (t, x, k) converges as ε → 0 to \({\bar{W}(t,x,k)}\) which satisfies the radiative transport equation. We prove that when the initial data is singular in the x variable, that is, W _ε (0, x, k) = δ(x)f(k) and \({f\in {\mathcal{S}}(\mathbb{R}^d)}\), then the laws of the rescaled fluctuation \({Z_\varepsilon(t):=\varepsilon^{-1/2}[W_\varepsilon(t,x,k)-\bar{W}(t,x,k)]}\) converge, as ε → 0+, to the solution of the same radiative transport equation but with a random initial data. This complements the result of [6], where the limit of the covariance function has been considered.     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

Forced snaking: Localized structures in the real Ginzburg-Landau equation with spatially periodic parametric forcing

We study spatial localization in the real subcritical Ginzburg-Landau equation u _t = m ₀ u + Q(x)u + u _xx + d|u|² u ?|u|⁴ u with spatially periodic forcing Q(x). When d>0 and Q ≡ 0 this equation exhibits bistability between the trivial state u = 0 and a homogeneous nontrivial state u = u ₀ with stationary localized structures which accumulate at the Maxwell point m ₀ = ?3d ²/16. When spatial forcing is included its wavelength is imprinted on u ₀ creating conditions favorable to front pinning and hence spatial localization. We use numerical continuation to show that under appropriate conditions such forcing generates a sequence of localized states organized within a snakes-and-ladders structure centered on the Maxwell point, and refer to this phenomenon as forced snaking. We determine the stability properties of these states and show that longer lengthscale forcing leads to stationary trains consisting of a finite number of strongly localized, weakly interacting pulses exhibiting foliated snaking.