Effect Of Crystal Anisotropy Research Articles

Elastic effects and phase segregation during the growth of thin alloy layers by molecular-beam epitaxy

We explore the effects of stress and strain on the composition modulations seen during the growth of thin solid films by molecular-beam epitaxy when phase separation is the driving mechanism for the concentration inhomogeneity. A top view of the growing thin film shows lamellar and hexagonal patterns of phase-separated domains, the elastic effects being directly responsible for the appearance of the hexagonal order. We find that in the lamellar regime, elastically deformed lamellae are separated by undeformed interfaces, while in the droplet phase, the soft component is deformed and wraps the hard component. We also discuss the effects of crystal anisotropy in our system.

Elastic Anisotropy Effect of Crystals on Polycrystal Fatigue Crack Initiation

Fatigue bands have been observed in both monocrystalline and polycrystalline metals. Extrusions and intrusions at the free surface of fatigued specimens are favorable sites for fatigue crack nucleation. Previous studies (Lin and Ito, 1969; Lin, 1992) mainly concerned the fatigue crack initiation in aluminum and its alloys. The elastic anisotropy of individual crystals of these metals is insignificant and was accordingly neglected. However, the anisotropy of the elastic constants of some other metallic crystals, such as titanium and some intermetallic compounds, is not negligible. In this paper, the effect of crystal anisotropy is considered by using Eshelby’s equivalent inclusion method. The polycrystal analyzed is Ni3Al intermetallic compound. The plastic shear strain distributions and the cumulative surface plastic strain in the fatigue band versus the number of loading cycles were calculated, and the effect of crystal anisotropy on the growth of the extrusions was examined.

Crystal optic effects in absorption of x-radiation

In this paper, the effect of crystal anisotropy on absorption of x-radiation is investigated. A formula is obtained describing the absorption of x-radiation by a biaxial crystal. Crystal optic effects are considered in the x-ray region of the spectrum. A mechanism is proposed for the dependence of the fine structure of x-ray absorption on the sample thickness in an anisotropic crystal. The effect of the crystal anisotropy on the x-ray fluorescence is investigated in the case of a uniaxial crystal.

Effect of Crystal Anisotropy on Infrared Hole Transitions in Uniaxially Stressed Semiconductors

AbstractPeculiarities of permittivity are studied for semiconductors with degenerate band structure modified by the uniaxial compression which induces valence band splitting. For [001] and [111] stress orientations cubic crystals become uniaxial, whereas for the [110] stress orientation they become biaxial. The contribution of intersubband hole transitions to the permittivity and the absorption coefficient is found to be significantly anisotropic in the frequency range corresponding to the subband splitting energy. Therefore, studying birefringence for different stress orientations may allow deformation potentials and stiffness constants to be determined.

Vortex lattice structures in YBa2Cu3O7

We describe small-angle neutron scattering (SANS) studies of vortex structures in the high T c superconductor YBa 2 Cu 3 O 7 in the mixed state. The SANS technique is a unique tool for probing the crystallography of a flux line arrangement in the bulk sample that can measure the values of the characteristic lengths and the effect of defects on lattice arrangement and orientation extremely accurately. The effects of crystal anisotropy on the field distribution in a vortex line is the topic of this paper

Hardness Anisotropy of Rhombohedral Crystals of Calcite. Variation of Hardness with Orientation

AbstractThe variation of hardness of rhombohedral single crystals of calcite with orientation of longer diagonal of Knoop indenter with respect to direction [100] on a cleavage plane (100) is studied. The Knoop hardness number H which has a constant value in the range of high loads (40–80 g) varies with orientation A and quenching temperature. By following phenomenological approach, an empirical relation √HA = mA + C is developed from these studies. The effects of crystal anisotropy and thermal treatment of specimens after indentation are also discussed.

Lamellar eutectic growth of CBr 4-C 2Cl 6: effect of crystal anisotropy on lamellar orientations and wavelength dispersion

Directional solidification samples of eutectic alloys generally appear divided into numerous “eutectic grains”, i.e. regions of uniform orientation of the two solid phases. Differences of behavior from grain should provide information about the effect of crystal anisotropy on solidification dynamics of eutectics. In thin samples of CBr 4-C 2Cl 6, we observed two types of grains: “locked”, or epitaxial, grains and “floating” grains, with no epitaxy between the two solid phases. We present a systematic experimental study of the stationary basic state in floating grains. The parity of this state appears generally broken: within a grain, the lamellae are tilted to a small (⪅ 5°), but definite angle Φ S with respect to the pulling direction. Φ S and the wavelength λ S are grain dependent. The interpretation of this tilting as an effect of the weak anisotropy of the interface energies is supported by a perturbative analytical calculation, completely developed in the limit of small triple-point pinning angles. The phase diffusion coefficient ¢D(λ) is also calculated in this limit to account for the observed slowness of phase diffusion. Eutectic grain boundaries are permanent sources of instabilities and of λ-gradients which do not spread out by phase diffusion for the duration of experiments, and the principal source of λ dispersion.

Effect of anisotropic phonons on superconductivity

Effect of crystal anisotropy which results in the anisotropic phonon frequency distribution function has been studied on superconductivity in a strongly coupled superconductor. The dependence of the superconducting critical temperature, T c, on the degree of anisotropy is quite involved. In highly anisotropic systems superconductivity is suppressed. The expression for T c is related to the total mean square displacement of the vibrating ion, yielding the result that, for superconductivity, the phonon frequency distribution function from mean square displacement is preferred to that obtained from other studies for consistent physical parameters. Explicit calculations for 67Zn are reported.

The effect of crystal anisotropy on the temperature-dependent mean square displacement, its temperature derivatives and second-order Doppler shift in zinc up to 600 K

Anisotropic mean square displacements, their temperature derivatives and second-order Doppler shift in the temperature range 0-600 K have been calculated in zinc by making use of the recently suggested anisotropic phonon frequency distribution function (1989) which takes into account the presence of planar modes. The calculated values of both the anisotropic mean square displacements and their temperature derivatives at various temperatures are in reasonable agreement with the corresponding experimental results. The effect of planar modes is found to be significant in the entire temperature range for all the three parameters studied.

Low‐frequency Raman and infrared scatterings in single crystals of sodium acid phthalate, NaC8H5O4 · ½H2O

AbstractPolarized, low frequency (5–400 cm−1) Raman scattering spectra in single crystals of sodium acid phthalate (NaAP) were measured at 295 and 115 K. Similarly, infrared scattering measurements were performed by FTIR reflection and transmission techniques at room temperature. Symmetry assignments and band descriptions consistent with the crystal structure of NaAP are reported. The effects of crystal anisotropy on polar phonons and LOTO splittings were observed and are commented upon.

Effect of crystal anisotropy on superconductivity in zinc

Abstract The effect of crystal anisotropy on superconductivity in zinc has been studied making use of the recently observed highly anisotropic vibrations of a zinc atom in its crystal. The effect of crystal anisotropy on superconductivity turns out to be quite involved and significant.

Effect of crystal anisotropy on superconductivity in zinc

The effect of crystal anisotropy on superconductivity in zinc has been studied making use of the recently observed highly anisotropic vibrations of a zinc atom in its crystal. The effect of crystal anisotropy on superconductivity turns out to be quite involved and significant.

Collective modes and a theory of response ofd-wave superconductors

We present a theory of the response ofd-wave superconductors to weak applied fields, by taking account of the Coulomb interaction and all the collective degrees of freedom as well as crystal symmetry. We choose two representative phases: the dγ phase, which has point nodes in the energy gap, and theY2−1 phase, which has line as well as point nodes. The former is a self-consistent solution for cubic as well as spherical symmetries and the latter is one for spherical, cubic, and hexagonal symmetries. We obtain obviously gauge-invariant expressions for the order-parameter fluctuations and the currents, having forms common not only to thed-wave states, but also to thep-wave states studied earlier. We also investigate the collective excitations; in the long-wavelength limit for spherically symmetric systems, there are, on the frequency-temperature plane, seven branches for eachd-wave phase considered, in addition to the common plasma mode and orbital Goldstone modes resulting from the spontaneous breakdown of the rotational invariance. In theY2−1-phase two eigenmodes are found to become gapless at a finite temperature, below which they are purely imaginary. This implies instability of the phase. The effect of crystal anisotropy on the collective spectra is also studied.

Anisotropic magnetization in single crystal ErBa 2Cu 3O 7-x

Low temperature measurements of the magnetic properties of single crystals of ErBa 2Cu 3O 7-x are used to study the effect of crystal anisotropy on the superconductivity of this material. The crystals, with a T c of 60 K, show marked anisotropy in magnetization versus applied magnetic field and in magnetization versus temperature, with superconductivity primarily occuring in the ab plane.

Microcracking in Ceramics Induced by Thermal Expansion or Elastic Anisotropy

The effect of crystal anisotropy on the formation of grain‐boundary microcracks is analyzed, by considering a planar array of hexagonal grains as a model of a polycrystalline ceramic. The stress singularities at triple‐grain junctions are analyzed by an asymptotic method as well as by a numerical solution, and the critical size of a grain‐boundary defect is investigated by a crack analysis. It is found that elastic anisot‐ropies can significantly increase the stress levels near triple points, which results in a smaller critical grain size for microcracking.

Effects of crystal anisotropy on magnetization and magnetic order in superconducting RBa2Cu3O7−x

Two distinct experiments are used to study the influence of crystal anisotropy on superconductivity in YBa2Cu3O7 and magnetic order in the superconducting state of ErBa2Cu3O7. Magnetization data on a single crystal of YBa2Cu3O7 reveal pronounced anisotropy. Analysis of the magnetization versus applied field hysteresis loops implies strong anisotropy of the critical current density. For ErBa2Cu3O7, neutron diffraction measurements indicate that the Er moments order two dimensionally at low temperatures (≈0.5 K), with chains of spins coupled ferromagnetically, while adjacent chains align antiparallel.

Magnetic Field‐Induced Transitions in the Mo4 Cluster Compounds GaMo4S8 and GaMo4Se8 Showing Heavy Fermion Behaviour

AbstractThe magnetization versus field curves of GaMo4X8 (X = S, Se) show magnetic field induced transitions at 5 and 1 kOe at 4.2 K, respectively. The critical fields at different temperatures are obtained from differential susceptibility measurements. Field cooled specimens are also investigated. A provisional magnetic phase diagram is constructred. The transition is ascribed to crystal anisotropy effects.

Collective Excitations in p- and d-Wave Superconductors

We study the collective excitations in p- and d-wave superconductors. For both cases we develop a theory of response in a gauge invariant way taking account of the collective degrees of freedom. Further we find that in the d-wave phases there also exist collective modes as in the p-wave phases. Effects of crystal anisotropy on the collective modes are also discussed.

Effect of Crystal Anisotropy on Heat Transfer During Melting and Solidification of a Metal

Effect of Crystal Anisotropy on Heat Transfer During Melting and Solidification of a Metal

Magnetostriction in Ni rods under torsion: Critical stress and crystal anisotropy effect

A contribution to the investigation of the stress effect on the saturation magnetostriction of polyerystalline rods stressed by torsion is presented. The critical torsional stress above which magnetostriction remains constant is found and the crystal anisotropy level, at various torsions, is estimated. As in the tensional case, the effect of crystal anisotropy at the critical stress has not been clearly interpreted so far. A study of the behaviour of the magnetization curve near saturation provides a possible explanation.