Temperature-time dependence of the spall strength of α-iron

The experimental data on the temperature dependence of the spall strength of α-iron have been generalized. The author’s and literature data have been interpreted in terms of the kinetic concept of the strength of solids. The temperature-time dependence of the strength of α-iron has been presented in time range of 10⁵–10^?9 s.     

Monte Carlo simulation of phosphorus diffusion in α-iron via the vacancy mechanism

Monte Carlo simulations of the vacancy and phosphorus (P) atom diffusion in body centred cubic (bcc) iron are presented. The input parameters for the calculations, namely the activation energies of atomic jumps, have been obtained using a potential set developed recently for a dilute Fe–P alloy using ab initio data. The diffusion coefficients entering equations for the fluxes of vacancies and solute atoms are evaluated. The results show that, in the temperature range of practical importance for P segregation, P atoms move down the vacancy gradient; hence, under irradiation conditions, vacancies should drag P atoms towards sinks of point defects. This is because of the high binding energy between a P atom and a vacancy in the first and second nearest neighbour sites from each other, which allows a vacancy to move around a P atom without loss of bonding and, hence, co-migrate with it.     

Anomalous behavior and phase transformation of α-GaOOH nanocrystals under static compression

The structural compression mechanism and compressibility of gallium oxyhydroxide, α-GaOOH, are investigated by in situ synchrotron radiation x-ray diffraction at pressures up to 31.0 GPa by using the diamond anvil cell technique. Theα-GaOOH sustains its orthorhombic structure when the pressure is lower than 23.8 GPa. The compression is anisotropic under hydrostatic conditions, with the a-axis being most compressible. The compression proceeds mainly by shrinkage of the void channels formed by the coordination GaO_3(OH)_3 octahedra of the crystal structure. Anomaly is found in the compression behavior to occur at 14.6GPa, which is concomitant with the equatorial distortion of the GaO_3(OH)_3 octahedra. A kink occurs at 14.6 GPa in the plot of finite strain f versus normalized stress F, indicating the change in the bulk compression behavior. The fittings of a second order Birch–Murnaghan equation of state to the P–V data in different pressure ranges result in the bulk moduli B_0= 199(1) GPa for P 14.6 GPa and B_0= 167(2) GPa for P 14.6 GPa. As the pressure is increased to about 25.8 GPa, a first-order phase transformation takes place, which is evidenced by the abrupt decrease in the unit cell volume and b and c lattice parameters.     

Anomalous dielectric behavior in the nematic and isotropic phases of a strongly polar–weakly polar binary system

We report permittivity studies in the isotropic liquid and anisotropic liquid crystalline (nematic or N) phases of a binary system, in which one component has molecules with a strongly polar longitudinal group, and the other has a weakly polar transverse group. The dielectric constant in the isotropic phase as well as its anisotropy in the N phase show, surprisingly, an anomalous non-monotonic dependence with concentration having a peak-like behavior for 10.2 mol% concentration of the weakly polar constituent. The transition between the two phases, being weakly first order, exhibits pretransitional effects signifying the appearance of the N-like regions in the isotropic phase. The coordinates of the maximum point of the convex shaped temperature-dependence of the dielectric constant in the isotropic phase, characteristic of strongly polar systems, also exhibit a non-monotonic dependence with concentration. Possible causes for these observations are discussed.     

Anomalous behavior of phonons in NbCu metallic superlattices

Brillouin and Raman scattering investigations have been performed on NbCu metallic superlattices. Anomalies have been observed in the surface acoustic phonons and bulk acoustic phonons versus superlattice wavelength. These anomalies occur simultaneously at the same superlattice wavelength ≈ 19 Å.     

Grain boundary segregation diagrams of α-iron

Based on thermodynamic analysis of interfacial segregation, the segregation enthalpy H ^o of a solute I in a given matrix was found to depend linearly on two mutually independent terms reflecting the type of interface and the solid solubility limit X _infI ^sup* at temperature T and can be written as In this equation, the structural dependence of interfacial segregation is contained in H ^*() which corresponds to the extrapolated segregation enthalpy of a solute with unlimited solubility in the matrix. The product [Tln(X _infI ^sup* )] is essentially constant with temperature, and can therefore be obtained from data for maximum solid solubility, [Tln(X _infI ^sup* )]_max. The parameter v>0 represents the relationship between the activity a _infI ^sup* of a solute at the bulk solid solubility limit in a given matrix and X _infI ^sup* , a _infI ^sup* =(X _infI ^sup* ) ^v , and is characteristic for the matrix. Using recent experimental data for silicon, phosphorus, and carbon segregation at well-characterized grain boundaries in oriented bicrystals of -iron, the averaged value was determined. Values of H ^*() range from -8 kJ/mol (general grain boundaries) up to +8 kJ/mol (special grain boundaries). These values are discussed and used for a more precise and generalized construction of grain boundary segregation diagrams of -iron.     

Lowest energy structures of self-interstitial atom clusters in α-iron from a combination of Langevin molecular dynamics and the basin-hopping technique

A combination of simulated annealing with Langevin molecular dynamics and the basin-hopping with occasional jumping (BHOJ) technique was used to systematically determine the most stable configurations of self-interstitial atom (SIA) clusters I _n (n = 1–38) in α-iron. In addition to the original BHOJ technique, we introduced an additional long jumping process in which a randomly selected less-bounded atom is moved to a neighbouring site of another SIA in the cluster to enhance the probability of locating the global minimum structure. With the obtained putative lowest energy structures, the binding energies as a function of cluster size were estimated. We also determined the sizes of particular stable clusters based on their geometrical symmetry. Furthermore, the values were extrapolated based on accurately determined formation energies, and are available for immediate use in kinetic Monte Carlo or rate theory models.     

SIA energetic and structural morphology of α-iron

In this paper, the stability of various atomic configurations containing a self-interstitial atom (SIA) in a model representing α-iron is investigated. From the energy panorama maps of the SIA located in possible non-equivalent interstitial sites, six relatively stable self-interstitial sites are found, whose structures and formation energies have been described and calculated using the modified analytical embedded atom method and molecular dynamics. The simulation results indicate that the [110] dumbbell interstitial is the energetically most favorable configuration, which is in good agreement with the experimental and ab initio results, and the distances between two displaced atoms that compose the [100], [110] and [111] direction dumbbells have been computed to be 0.68a, 0.65a and 0.29a, respectively, not all being about 0.75a apart. The relaxed displacements up to the fifth-nearest-neighbor atoms around the SIA in O interstitial position are also calculated.     

Phase relations and probabilities of α-particle formation in the surface region of even-even nuclei

The concept of the probability of formation W_c of particles in the surface region of nuclei is used in a classification of transitions of even-even deformed nuclei (226 A 254) to the first four levels of the ground-state rotational band of the daughter nuclei with allowance for coupling of the decay channels. The calculated values of W_c are compared with the analogous quantities in spherical nuclei and are used as a basis for the classification of transitions in deformed nuclei. It is concluded that the phase factors of the wave functions with L=0 and 2 are positive, while those with L=4 are positive for the investigated isotopes of Th, U, and Pu and negative for Cm, Cf, and Fm. The fractions of transitions with L=4 are predicted for a number of isotopes.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 49–54, July, 1980.     

Anomaly in the field dependence of the anisotropic magnetic susceptiblity of a single-grained α-Mn

A kink was observed near 20 kOe in the field dependence of the magnetization in a single-grained α-Mn without a magnetic hysteresis below the Neel temperature in an accurate magnetization measurement below 80 kOe. It was observed along [1 0 0], [1 1 0] and [1 1 1] crystallographic directions. The field dependence of the magnetization above 40 kOe extrapolates to positive finite magnetization at null field. The kink suggests a weak metamagnetism induced by the external magnetic field. A small but clear anisotropy was observed between the weak-field susceptibilities along [1 0 0] and [1 1 0]/[1 1 1] directions. A previously reported large susceptibility anomaly was not affirmed between 90 and 270 kOe.     

Effect of alloying on the self-diffusion activation energy in γ-iron

The experimental data on the self-diffusion coefficient of austenite with different chemical compositions obtained by the radioactive isotope method have been analyzed quantitatively. The self-diffusion activation energy in pure γ-iron is shown to be ∼312 kJ/mol. Alloying of austenite with such elements as Mn, Mo, Nb, Ti, and Si (to a lower degree) increases the self-diffusion activation energy, and alloying with C, V, or Cr (for the element content ≥3 at %) decreases it. The empirical formula is derived for calculation of the self-diffusion activation energy in austenite solid solutions with complex composition.     

Simulation of the interaction between an edge dislocation and ⟨111⟩ interstitial dislocation loops in α-iron

ABSTRACT

The dependence of the interactions of intermediate-size ½<111> self-interstitial atom (SIA) loops with an edge dislocation on strain rate and temperature was investigated by molecular dynamics (MD) simulations for the interatomic potential derived by Ackland et al. (A97). For low temperatures (T?=?1?K), the mechanisms of the interactions were in agreement with recent literature. It was shown that a second passing of the dislocation through the loop led to a different mechanism than the one that occurred upon first passing. Since these mechanisms are associated with different SIA loop sizes, and since the loop lost a number of SIAs upon first interaction, it was deduced that the dividing threshold between large and small loops (rendering them strong or weak obstacles, respectively) is at the vicinity of the loop size studied (169 SIAs). For higher temperatures (T?=?300?K), the strain rate dependence proved strong: for low strain rates, the dislocation absorbed the loop as a double super-jog almost immediately and continued its glide unimpeded. For a high strain rate, the dislocation was initially pinned due to the formation of an almost sessile segment leading to high critical stress.     

Anomalous coverage behavior of the CsAg distance on CsAg(110)

The position of Cs on the (1 × 2) missing row reconstructed Ag(110) surface was determined by X-ray diffraction for two different Cs-coverages: θ_Cs = 0.2 and θ_Cs = 0.3. The Cs was found to be adsorbed in incommensurate chains in the troughs of the missing row with an average adsorption height of 1.7 Å (θ_Cs = 0.2) and 1.4 Å (θ_Cs = 0.3) above the topmost Ag layer. The apparent contradiction to the classical picture of alkali adsorption, which expects an increase of the Cs adsorption height with coverage, might be partly resolved by introducing a fraction of commensurately adsorbed Cs at θ_Cs = 0.2.     

Study of group velocity in the negative refractive index region in three level closed Λ system via spontaneously generated coherence

A new approach is suggested to realize simultaneous negative permittivity and permeability in a three level closed system with incoherent pumping via spontaneously generated coherence (SGC). In this system the negativity of the real part of magnetic permeability can be achieved in the presence of SGC whereas in the absence of SGC it is positive. Thus the SGC makes the system a negative index medium (NIM) in a band of frequency range. The position and the band of the frequency region of negative refraction can be manipulated by controlling the incoherent pump rate. We achieve FOM?=?7.91165. We have studied the group index in the negative refractive index region and have shown that the group velocity switches from superluminal to subluminal mode in this region of negative refraction. We have shown that the negative refractive index can be realized in a heteronuclear molecule.     

Anomalies in the elastic properties of silicious iron single crystals at pressures of up to 9 GPa and the α−ɛ phase transformation

A Fe+5.07 at.%Si single crystal has been studied by ultrasonic-pulse technique. Its density and elastic constants were determined for p=0 and T=293 K. The dependence of the elastic properties of silicious iron on Si concentration was constructed. The compression, the effective elastic constants, and the Grüneisen parameters were measured at hydrostatic pressures of up to 9 GPa. It was found that for p=0, and . The elastic constants c ₄₄ and c′ increase linearly with pressure by 19.3 and 18.2% by p=9 GPa. The elastic anisotropy does not vary with pressure. For p>4 GPa, c ₁₁, c ₁₂, and K _S were observed to increase nonlinearly with decreasing pressure derivative. The Grüneisen parameter γ _LA decreases with pressure down to 0.70 at 9 GPa to become negative when extrapolated to the region of the α−ɛ phase transformation. The anomalies in c ₁₁ and the negative values of γ _LA for p>11 GPa indicate that the phase transformation in silicious iron at 13.5 GPa can take place by the crystallographic mechanism of the α−ɛ transformation in pure iron, i.e. by lattice compression in the [001] direction and shearing of the (110) planes along or . An assumption is put forward that pressure gives rise in silicious iron to sp-d hybridization, which results in increased screening of the ion-ion interaction and in anomalies in elastic properties. Similar phenomena are expected to occur in pure bcc Fe as well. Fiz. Tverd. Tela (St. Petersburg) 41, 516–522 (March 1999)     

Absorption spectrum of HDO in the 1.06 μm region at a temperature of 1000 K

In the 9387–9450 cm^–1 region at temperatures of 300–1000 K, we have used an intracavity laser spectrometer based on a neodymium laser with threshold sensitivity to absorption 10^–8 cm^–1 and spectral resolution 0.035 cm^–1 to study the absorption spectrum of D₂¹⁶O, H₂¹⁶O, and HD¹⁶O vapor. The high-temperature spectrum contains more than 450 absorption lines, 240 of which are assigned to the HDO isotopomer. The absorption lines of HDO were identified and belong to nine vibrational transitions: 3ν₂ +ν₃, 2ν₁ + 3ν₂, 2ν₁ + ν₃, 4ν₂ + ν₃, 7ν₂, ν₁ + 2ν₂ + ν₃, ν₁ + 5ν₂, ν₁ + 2ν₂, and 3ν₃ – ν₂.     

An analytical model for the polarization of synchrotron radiation in a soft X-ray region

Conventionally, the polarization of a synchrotron soft X-ray beam is measured through a polarimeter based on multilayer optical elements. The major drawback of the traditional approach is the difficulty in comparing different configurations due to the misalignment of each incident angle. In this paper, a new analytical model, based on the variation of reflectivity for different incident angles, is established to facilitate the extraction of important polarization-related information, i.e. angular distribution of polarization components, a tiny change of the direction of azimuth rotation axis of polarizer, etc.