Mechanism of the FCC–BCC martensitic transformation with the fastest rearrangement of close-packed planes. II. Orientation relationships

The dynamic theory of the formation of martensite crystals as a result of an fcc (γ) – bcc (α) transformation that implies the fastest rearrangement of {111}γ planes into {110}α planes is used to derive interphase orientation relationships. It is shown that the orientation relationships, the macroshear, and the habit plane are uniquely related to the path of the martensitic reaction that is specified by the driving wave process. The dependence of orientation relationships on the elastic properties of the original fcc lattice is found analytically. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 42–47, November, 2008.     

Calculation of electronic spectra of porphin and its derivatives by a modified INDO/S method

Quantum-chemical calculations of excited electronic states of porphin (H₂P) and Mg-porphin (MgP) have been carried out in the framework of the INDO/S method with varying off-diagonal matrix elements of the one-electron Hamiltonian {ie027-01} and electron-electron interaction integrals {ie027-02} as functions of the internuclear distance. It has been found that a simultaneous increase in the π-type overlap factor for {ie027-03} and decrease in the {ie027-04} integrals, as compared with {ie027-05} calculated by the Nishimoto-Mataga formula, make it possible to reproduce the positions of the Q-and B-transitions in the experimental absorption spectrum with a precision of ∼300 cm⁻¹. In this case, the N_x-transition intensity of the H₂P molecule is halved, which means that only two B-transitions should be related to the Soret band as in the four-orbital model. Using the proposed parameterization (INDO/Sm), electronic spectra have been calculated for a number of porphyrin compounds including chlorine, bacteriochlorin, tetrabenzoporphin, and tetraazaporphin. The results obtained agree with the experimental data to an accuracy of 300–700 cm⁻¹ whereas the accuracy of the standard INDO/S calculation is no better than 3000 cm⁻¹. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 28–35, January–February, 2008.     

Crystallographic anisotropy in chemisorption: Nitrogen on tungsten single crystal planes

A molecular beam technique for the determination of sticking probabilities and surface coverages was used in earlier work to investigate the adsorption of nitrogen on tungsten {110}, {111} and {100} single crystal planes. In the present paper these studies have been extended to the {310}, {320} and {411} planes. Absolute sticking probabilities and adatom surface coverages are reported for crystal temperatures between 90 K and 960 K. Crystallographic anisotropy in this system is exemplified by zero coverage sticking probabilities with the crystal at room temperature: {110}, 1̃0^?2; {111}, 0.08; {411}, 0.4; {100}, 0.59; {310}, 0.72; {320}, 0.73. Results for planes on the [001] zone are quantitatively described by a general model developed for adsorption on stepped planes as an extension to the precursor-state order-disorder model for adsorption kinetics of King and Wells. It is shown that nitrogen dissociation only takes place at vacant pairs of {100} sites, but that subsequently the chemisorbed adatoms so formed may migrate out onto {110} terraces. The results are critically analysed in terms of the available LEED and work function data for nitrogen on tungsten single crystal planes, and the general model developed by Adams and Germer.     

On the mass function of light quarks

A mass function model of light quarks based on non-perturbative solutions of the Schwinger-Dyson equations is considered. According to this model, for small arguments the mass function has a constant value close to the constituent quark mass and then quickly decreases entering into the perturbative regime. It is demonstrated that this behavior of the mass function allows good agreement with experimental value of weak pion decay constant {ie730-01} and phenomenological value of the chiral condensate {ie730-02} to be obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 64–68, July, 2008.     

Hadrons in compact stars

We discuss β-equilibrated and charge neutral matter involving hyperons and {ie817-1} condensates within relativistic models. It is observed that populations of baryons are strongly affected by the presence of antikaon condensates. Also, the equation of state including {ie817-2} condensates becomes softer resulting in a smaller maximum mass neutron star     

铁的冲击相变机制的分子动力学研究

 用分子动力学方法模拟计算了在冲击波加载条件下,单晶铁中的结构相变（由体心立方结构α相到六角密排结构ε相）,相互作用势采用铁的嵌入式原子势（EAM）,单晶铁样品的尺寸为28.7 nm×22.9 nm×22.9 nm,总原子数为1.28×10⁶个。通过推动一个运动活塞对静止靶的作用来产生冲击压缩,加载方向沿单晶铁的[100]晶向。通过对原子位置的追踪,揭示了铁的冲击相变机制,计算结果表明相变机制包括两步：首先是在{011}面上的原子受到沿〈100〉晶向的压缩,使{011}面转化成正六角形密排面;然后是在{011}面上原子沿〈0-11〉晶向的滑移,完成由bcc结构到hcp结构的相变。同时发现滑移面只出现在与冲击波加载方向平行的(011)和(0-11)面上。     

Reply to comay’s "relativity versus the longitudinal magnetic field of the photon"

Poincaré group electrodynamics is {ie255-1} conserving and Lorentz covariant under all conditions by definition. Examples are given of these properties. Comay’s comment is incorrect: any {ie255-2} conserving field theory that is Lorentz covariant is consistent with special relativity, whose underlying group is the Poincaré group.     

The energy dependence of the {111} and {100} tilt grain boundaries on disorientation angle in Ni<Subscript>3</Subscript>Al

Dependence of the energy of {111} and {100} boundaries on tilt angle θ is investigated by the molecular dynamics method using intermetallic Ni₃Al as an example. It is shown that the energy (per single grain dislocation) of grain boundaries in the {111} planes is higher than that of the grains located in the {100} planes. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 33–35, November, 2007.     

First-principles characterisation of the pressure-dependent elastic anisotropy of SnO2 polymorphs

Using DFT calculations, this study investigates the pressure-dependent variations of elastic anisotropy in the following SnO₂ phases: rutile-type (tetragonal; P4₂/mnm), CaCl₂-type (orthorhombic; Pnnm)-, α-PbO₂-type (orthorhombic; Pbcn)- and fluorite-type (cubic; Fm-3m). Experimentally, these polymorphs undergo sequential structural transitions from rutile-type → CaCl₂-type → α-PbO₂-type → fluorite-type with increasing pressure at 11.35, 14.69 and 58.22 GPa, respectively. We estimate the shear anisotropy (A₁ and A₃) on {1?0?0} and {0?0?1} crystallographic planes of the tetragonal phase and (A₁, A₂ and A₃) on {1?0?0}, {0?1?0} and {0?0?1} crystallographic planes of the orthorhombic phases. The rutile-type phase shows strongest shear anisotropy on the {0?0?1} planes (A₂ > 4.8), and the degree of anisotropy increases nonlinearly with pressure. In contrast, the anisotropy is almost absent on the {1?0?0} planes (ie A₁ ~ 1) irrespective of the pressure. The CaCl₂-type phase exhibits similar shear anisotropy behaviour preferentially on {0?0?1} (A₃ > 5), while A₁ and A₂ remain close to 1. The α-PbO₂-type phase shows strikingly different elastic anisotropy characterised by a reversal in anisotropy (A₃ > 1 to < 1) with increasing pressure at a threshold value of 38 GPa. We provide electronic density of states and atomic configuration to account for this pressure-dependent reversal in shear anisotropy. Our study also analyses the directional Young’s moduli for the tetragonal and orthorhombic phases as a function of pressure. Finally, we estimate the band gaps of these four SnO₂ phases as a function of pressure which are in agreement with the previous results.     

Features of the dispersion characteristics of nonuniform plasma waveguides in a longitudinal magnetic field

We study the features of the dispersion curves and field structures of the fundamental axisymmetric mode of nonuniform layered plasma waveguides in a longitudinal magnetic field. It is shown that the presence of sharp boundaries between layers leads to the appearance of additional branches of the dispersion curves in the frequency range ω _Be < ω < ω_UH(0), where ω_Be is the electron gyrofrequency and ω_UH(0) is the upper-hybrid resonance frequency for the near-axis region of a nonuniform waveguide. The fields of eigenmodes corresponding to these branches comprise resonance structures near the sharp plasma-density variation at which the upper-hybrid resonance conditions are satisfied and plasma waves are excited. The frequency interval of such a branch is limited by the resonant frequencies of the neighboring uniform layers. It turns out that in the case of a strong magnetic field ({ie392-01}, where ω_p is the plasma frequency having the value {ie392-02} in the near-axis region of a nonuniform waveguide), the fundamental-mode field is localized in the near-axis region of a nonuniform waveguide, whereas in the opposite case {ie392-03}, the maximum wave fields are localized in either the upper-hybrid resonance region or the outer (near-boundary) layer of the waveguide if there is no resonance region. It is found that the whistler (helicon) contribution to the field structure of the fundamental axisymmetric mode is very small for narrow nonuniform waveguides (b < λ₀, where b is the waveguide radius and λ₀ is the wavelength in free space) if the plasma density on the axis is high compared with the cutoff density {ie392-04}. We present one of the possible explanations for the effect of narrowing of the plasma channel of a high-frequency whistler-range discharge with distance from a source in the increasing magnetic field. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 5, pp. 434–446, May 2008.     

The Maslov correction in the semiclassical Feynman integral

The Maslov correction to the wave function is the jump of $ \left( { - \frac{\pi } {2}} \right) $ \left( { - \frac{\pi } {2}} \right) in the phase when the system passes through a caustic. This can be explained by studying the second variation and the geometry of paths, as conveniently seen in Feynman’s path integral framework. The results can be extended to any system using the semiclassical approximation. The 1-dimensional harmonic oscillator is used to illustrate the different derivations reviewed here.     

Photoluminescence of SiV centers in CVD diamond particles with specific crystallographic planes

We prepared the isolated micrometer-sized diamond particles without seeding on the substrate in hot filament chemical vapor deposition. The diamond particles with specific crystallographic planes and strong silicon-vacancy(SiV) photoluminescence(PL) have been prepared by adjusting the growth pressure. As the growth pressure increases from 2.5 to 3.5 kPa,the diamond particles transit from composite planes of {100} and {111} to only smooth {111} planes. The {111}-faceted diamond particles present better crystal quality and stronger normalized intensity of SiV PL with a narrower bandwidth of 5 nm. Raman depth profiles show that the SiV centers are more likely to be formed on the near-surface areas of the diamond particles, which have poorer crystal quality and greater lattice stress than the inner areas. Complex lattice stress environment in the near-surface areas broadens the bandwidth of SiV PL peak. These results provide a feasible method to prepare diamond particles with specific crystallographic planes and stronger SiV PL.     

Proton momentum distributions in the 7Li nucleus in a potential cluster model

Distributions of the proton momentum in the ⁷Li{αt} → p + ⁶He{αnp} fragmentation channel were, along with the corresponding widths and spectroscopic factors, calculated in the αnn model representation of wave functions of the ⁶He nucleus in the (0⁺,1) ground and (2⁺,1) excited states. The results are compared to the available theoretical calculations and experimental NIKHEF data on the ⁷Li(e,e′p)⁶He electron-induced proton knock-out process.     

Splitting of dislocations in b.c.c. metals on {110} planes

Three possible splittings of a screw dislocation on {110} planes of a metal with a b.c.c. lattice are proposed, their total elastic energy is calculated and the dependence of the splitting width on the stacking fault energy is studied.We wish to express our thanks to B. esták, CSc., and S. Libovický for valuable comments and M. Jiincová for her help in carrying out the numerical calculations.     

Shift photocurrent induced by two-quantum transitions

A theory of the shift current induced by direct two-photon and indirect one-photon absorption is developed for noncentrosymmetric crystals. A formula is derived for the microscopic shifts of Bloch electrons induced by two-quantum processes. It is shown that the ratio of the two-photon photocurrent at the photon frequency ω to the photocurrent induced by direct one-photon transitions at the photon frequency 2ω, as compared to the corresponding absorption-rate ratio, contains a large factor {ie152-1}ω/(2{ie152-2}ω − E _g), where E _g is the bandgap; i.e., these photocurrent can be comparable in order of magnitude. For crystals of T _d symmetry, the photocurrents induced by one- and two-photon absorption are compared in terms of polarization dependence.     

钼单晶体的范性形变

在本文中,用金相和X射线方法,研究了24个取向不同的钼单晶体在-80℃(-50℃)、27℃、1000℃和～2000℃拉伸后的情况。分析研究的结果,认为观察到的{112}、{123}、{145}等滑移痕迹,是由于在两组不平行的{110}面上,沿着同一个<111>方向组合滑移后构成的外观面貌,而滑移面是密排的{110}面。外观滑移面(从滑移痕迹测定出的)会随样品取向不同而发生变化。当变形温度改变时,同一个样品的外观滑移面可能改变,也可能不改变,这要由样品的取向来决定。 关键词：     

Diamond cleavage: importance to high pressure research

The extraordinary properties of diamond make it the number-one choice for anvils in high pressure experiments involving anvil cells. In much of the literature on the properties of diamond the only cleavage mentioned is {111}. However, experience has shown that diamond anvils made with their [001] axis oriented in line with the principal stress axis of the anvil or at a small angle to it often failed with flat faces having {110} orientations; a cleavage plane is reported in some publications. Analysis of the anisotropy of strength and Poisson ratio in diamond has shown that such orientations do, indeed, favor initial failure on {110} cleavage planes. This analysis, in conjunction with stereographic projections of the {111} and {110} cleavage planes, suggests that a 27° tilt of the [001] axis with respect to the linear stress axis by rotation around the [100] or [010] axis should provide significantly greater resistance to failure by cleaving.     

Development of etch hillocks on different Si(h k l) planes in silicon anisotropic etching

The connection between the way of development and appearance of mesa structures and typical hillocks developing during anisotropic etching of monocrystalline silicon in 5 M KOH saturated with isopropanol has been studied both theoretically and experimentally. A simple geometrical model of mesa formation was presented. Then, the process of hillock growth in result of mesa transformation caused by etch mask underetching was analyzed. At the second part of the paper, the model of hillocks formation was verified experimentally. For this purpose, a series of experiments with etching of mini-mesas through the masks with various patterns in the conditions favoring hillock formation was carried out. It was shown that at the final stage of the etching process the mesas transform into hillocks, bounded by the planes close to {1 1 1}. Probably at the first stage of hillocks formation, mini-mesas develop. Such stable mini-mesas, produced in the presence of random micro-masks, may transform into typical hillocks in effect of successive releasing of {1 1 1} mini-faces. It seems that the process of hillock formation is similar to mesa etching.

The shapes of hillocks produced on the substrates with different from (0 0 1) crystallographic orientations have been also analyzed. The similarities of the hillocks and intentionally prepared mesas were underlined. It was stated that the morphologies of hillocks are strictly connected with crystallographic orientation of etched substrate. Different shapes of hillocks developing on the substrates with different crystallographic orientations, reflect the arrangement and inclination of {1 1 1} planes on considered substrate.     

Molecular dynamics simulation of the plastic behavior anisotropy of shock-compressed monocrystal nickel

Molecular dynamics simulations were used to study the plastic behavior of monocrystalline nickel under shock compression along the [100] and [110] orientations. The shock Hugoniot relation, local stress curve, and process of microstructure development were determined. Results showed the apparent anisotropic behavior of monocrystalline nickel under shock compression. The separation of elastic and plastic waves was also obvious. Plastic deformation was more severely altered along the [110] direction than the [100] direction. The main microstructure phase transformed from face-centered cubic to body-centered cubic and generated a large-scale and low-density stacking fault along the family of { 111 } crystal planes under shock compression along the [100] direction. By contrast, the main mechanism of plastic deformation in the [110] direction was the nucleation of the hexagonal, close-packed phase, which generated a high density of stacking faults along the [110] and[1?10] directions.