Orientation Of Crystal Axes Research Articles

Orientation dependence of γ-ε-α′ martensitic transformations in single crystals of austenitic stainless steel with a low stacking-fault energy

X-ray diffraction and electron microscopy were used to study the development of the γ-ɛ martensitic transformation (MT) upon tensile deformation of single crystals of (I) the Fe-17% Cr-12% Ni-2% Mn-0.75% Si and (II) Fe-18% Cr-12% Ni-2% Mo-0.015% C (wt %) austenitic stainless steels as a function of the crystal-axis orientation and the test temperature T. It has been shown that a decrease in the test temperature to T<173 K in single crystals of steels I and II with a low stacking fault energy (γ0=0.01–0.015 J/m2) leads to a γ-ɛ-α’ MTs upon plastic deformation. It has been established that the degree of deformation preceding the γ-ɛ MT depends on the crystal-axis orientation and the γ0 magnitude. In the [011] and \([\bar 1 11]\) crystals, the γ-ɛ MT upon tension is developed already at early stages of plastic flow, at ɛ≤3%, whereas in the \([\bar 1 23]\) and [012] crystals it occurs after a substantial deformation by slip, at ɛ=16–70%. In the [001] crystals, no γ-ɛ MT is revealed by X-ray diffraction, but 1–2% ɛ phase is observed by electron microscopy. The physical cause for the observed orientation dependence in the γ-ɛ MT is related to the effect of external stresses σ on the degree of splitting of perfect dislocations a/2〈110〉 to Shockley partial dislocations a/6〈211〉, which form nuclei of the ɛ phase.

Correlation between interfacial structure and c-axis-orientation of LiNbO3 films grown on Si and SiO2 by electron cyclotron resonance plasma sputtering

Thin films of crystalline lithium niobate (LN) grown on Si(100) and SiO2 substrates by electron cyclotron resonance plasma sputtering exhibit distinct interfacial structures that strongly affect the orientation of respective films. Growth at 460–600°C on the Si(100) surface produced columnar domains of LiNbO3 with well-oriented c-axes, i.e., normal to the surface. When the SiO2 substrate was similarly exposed to plasma at temperatures above 500°C, however, increased diffusion of Li and Nb atoms into the SiO2 film was seen and this led to an LN–SiO2 alloy interface in which crystal-axis orientations were randomized. This problem was solved by solid-phase crystallization of the deposited film of amorphous LN; the degree of c-axis orientation was then immune to the choice of substrate material.

Orientational dependence of shape memory effects and superelasticity in CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals

The dependence of deforming stresses, shape memory effect (SME), and superelasticity (SE) on the orientation of the single crystal axis, test temperature, and disperse particle size is examined for CoNiGa, NiMnGa, CoNiAl, FeNiCoTi, and TiNi single crystals. The orientational dependence of SME, SE, and temperature interval of the development of martensitic transformations (MT) under loading and SE is established. The influence of disperse particles on magnitudes of SME, SE, and mechanical hysteresis is discussed.

Synthesis of fibrous TiO2 from layered protonic tetratitanate by a hydrothermal soft chemical process

Fibrous TiO 2 (anatase) was prepared by a hydrothermal soft chemical process using H 2 Ti 4 O 9 ·0.25H 2 O as a template precursor. The influence of reaction time, temperature and precursor concentration on the phase formation, morphology and crystal-axis orientation were studied. The results have shown that fibrous anatase can be obtained at 220 °C for 24 h with the precursor concentrations in the range of 0.025–0.100 M, and that particles had diameters of 0.2–1 μm and lengths of 2–20 μm. The fibrous TiO 2 anatase prepared by this method showed a high orientation along a -axis direction. X-ray diffractometer (XRD) and SEM analyses have indicated that in situ transformation mechanism dominated the entire hydrothermal process but dissolution–recrystallization also occurred on the surface of the particles.

Plastic deformation of nitrogen-containing austenitic stainless steel single crystals with low stacking fault energy

On single crystals of austenitic stainless steel with nitrogen C N =0-0.5 wt.% the stages of stress-strain curves, work-hardening coefficient, deformation mechanism - slip and twinning, the developing of dislocation structure in dependence on crystal tensile axis orientation, test temperature, nitrogen concentration have been investigated. The type of dislocation structure (cellular or planar) and deformation mechanism (slip or twinning) have been shown to determine by the value of matrix stacking fault energy, by the level of friction forces due to solid solution hardening with nitrogen atoms and by the crystal orientation. It has been established that the contribution of mechanical twinning to the plastic deformation of steel crystal increases with nitrogen content, and in high-strength states at concentration of interstitial atoms C>0.5 wt.% mechanical twinning develops from early stages of deformation and determines work-hardening coefficient. The achievement of high level of deformation stresses due to the solid solution hardening with nitrogen atoms in combination with low values of γ 0 results in twinning in [001] orientations.

Synthesis of fibrous TiO 2 from layered protonic tetratitanate by a hydrothermal soft chemical process

Fibrous TiO 2 (anatase) was prepared by a hydrothermal soft chemical process using H 2Ti 4O 9·0.25H 2O as a template precursor. The influence of reaction time, temperature and precursor concentration on the phase formation, morphology and crystal-axis orientation were studied. The results have shown that fibrous anatase can be obtained at 220 °C for 24 h with the precursor concentrations in the range of 0.025–0.100 M, and that particles had diameters of 0.2–1 μm and lengths of 2–20 μm. The fibrous TiO 2 anatase prepared by this method showed a high orientation along a-axis direction. X-ray diffractometer (XRD) and SEM analyses have indicated that in situ transformation mechanism dominated the entire hydrothermal process but dissolution–recrystallization also occurred on the surface of the particles.

Room temperature measurements of the 3D orientation of single CdSe quantum dots using polarization microscopy.

Simple far-field emission polarization microscopy reveals that the emission transition dipole of CdSe colloidal quantum dots (QDs) is twofold degenerate at room temperature. We measure, model, and compare polarization anisotropy statistics of CdSe QDs and DiI (a one-dimensional emitter). We find excellent agreement between experiment and theory if the transition dipole of CdSe QDs is assumed to be twofold degenerate. This implies that the three-dimensional orientation of the unique crystal axis in QDs can be determined at room temperature with polarization microscopy. We describe an optical setup to measure four polarization angles of multiple single QDs simultaneously and in real time (approximately equal to 16 Hz). We use this setup in a proof-of-concept experiment to demonstrate that the rotational motion of QDs can be monitored in various host matrices.

Surface Modification by Grinding ZnO with Crystal Axis Orientation

Surface Modification by Grinding ZnO with Crystal Axis Orientation

Anisotropy of quadratic magneto-optic effects in reflection

Quadratic or second-order magneto-optic effects in reflection significantly effect in-plane magnetization measurements. While the magneto-optic effects linear in magnetization are independent of orientation of cubic crystal axes, the amplitude and sign of the quadratic effects change significantly under crystal rotation. Theoretical formulas for the magneto-optic effects have been derived using a permittivity tensor including terms quadratic in magnetization. A method for separation of the diagonal and off-diagonal quadratic magneto-optic tensor components (G11−G12) and 2G44 is proposed. The theory was completed by an experimental observation of the quadratic effect anisotropy in an epitaxial Fe layer prepared on a MgO substrate. The influence of the magnetization components on the magneto-optic vector magnetometry is discussed for an interface, a single layer, and exchange coupled bilayer system for a general magnetization direction including the quadratic magneto-optic effect anisotropy.

Effect of grain alignment on magnetic properties of Hg(Re)-1223 superconductors

Alignment of HgBa 2Ca 2Cu 3Re 0.2O y (Hg(Re)-1223) powders was made in epoxy resin under a high magnetic field of 10 T to be confirmed by X-ray analysis. DC magnetizations and AC susceptibilities of the grain aligned specimen were measured by SQUID and PPMS magnetometers at temperatures of 5–110 K and under the field of 0–14 T for both field directions of B parallel and perpendicular to ab-plane. The magnetization width for B parallel to the c-axis ΔM c showed high values at low field, decreased rather rapidly with the magnetic field compared to that for B parallel to the ab-plane ΔM ab and became lower than ΔM ab above a crossing field B cr. Peak-heights of the imaginary parts of the AC susceptibilities χ″ were largest at B∥ c-axis. Non-aligned samples always showed intermediate characteristics between B∥ c-axis and B∥ ab-plane. Irreversibility fields of all samples were also evaluated. Correlations of the pinning mechanism with the crystal axis orientations are discussed.

Magnetically Induced Alignment of Ferro-Nematic Suspension on PVCN-F Layer

We have observed magnetically controlled anchoring of ferro-nematic suspensions (FNS) on a fluoro-poly(vinyl)-cinnamate (PVCN-F) layer. We found that with the application of a weak magnetic field to a cell filled with the ferro-suspension, we could induce an easy (orientational) axis of weak anchoring energy on the polymer surface. By varying the direction of the magnetic field, one can change the easy axis orientation of liquid crystal (LC). We believe that the magnetically induced alignment of the ferro-nematic suspension is caused by the precipitation of ferro-particles on the polymer substrate. As a result, this alignment can be manipulated by a small magnetic field. The developed system is very promising for ultra-sensitive magnetically controlled LC devices for information processing and storage.

Orientation effects accompanying the propagation of ultrarelativistic electrons through crystals

The results obtained by experimentally investigating the dynamics of the propagation of 1.2-GeV electrons through a thin silicon single crystal are discussed. The orientation dependences of electron scattering into a small solid angle, which are measured at various scattering angles, under conditions where the effects of crystallographic axes and planes manifest themselves are interpreted. It is shown that there are such electron-scattering directions for which the orientation “independence” of the scattering intensity with respect to a specific crystallographic plane is observed and that there also exists a crystal-axis orientation for which the region of a uniform angular distribution of the intensity is observed.

Coherent magnetization reversal of nanoparticles with crystal and shape anisotropy

We discuss coherent magnetization reversal in single-domain particles with cubic or uniaxial crystal anisotropy and present the derivation and simulation of the nucleation field in the important case of particles with shape anisotropy and a random orientation of a cubic crystal anisotropy axis. We analyze the interplay of shape and crystal anisotropy as a function of crystal orientation with respect to the applied field. In addition, we present simulations for particles with uniaxial crystal anisotropy and derive the values for remanence and coercive field of an ensemble of particles from calculated hysteresis loops in each case.

Magnetostriction of Tb–Dy–Fe alloy with different crystal axes orientation

Based on the principle of energy minimum, magnetostriction of Tb–Dy–Fe alloy with different crystal axes under different compressive stress has been calculated using a three-dimensional anisotropy domain rotation model. Simulated results show that the magnetostriction property of 〈1 1 1〉-oriented single crystal is the best; saturation magnetostriction up to 2378 ppm has been obtained under compressive prestress of 24 MPa, which is very close to the experiment results. Saturation magnetostriction properties of 〈1 1 2〉-oriented and 〈1 1 0〉-oriented single crystal are very close under lower compressive prestress, while the 〈1 1 0〉-oriented ones have higher magnetostriction than 〈1 1 2〉-oriented ones under higher compressive prestress. In lower magnetic field, 〈1 1 0〉-oriented crystals achieve jump effect (1018 ppm at 715 Oe under 10 MPa) prior to 〈1 1 2〉-oriented ones, which indicates that it has fairly better low-magnetic field properties. These results agree well with the experimental results in previous literatures.

Heat transport across the interface between normal metal and d-wave superconductor

Heat conductance and heat current across normal metal/d-wave superconductor (NID) interface are calculated in the framework of quasiclassical equations. The calculations are performed for different values of boundary transparencies and crystal axis orientation. It is shown that in contrast to N/s-wave boundary the heat conductance of transparent (D=1) NID interface is considerably larger and has a nonactivated form. Electronic heat current across NID structures is also calculated for different interface models taking into account the midgap states and the possibility of generating a gapless s-wave state in the vicinity of rough NID interface. It is shown that NID junctions cannot compete with analogous NIS devices in microrefrigerating and bolometer applications.

X-RAY DIFFRACTION RECIPROCAL SPACE AND POLE FIGURE CHARACTERIZATION OF CUBIC GAN EPITAXIAL LAYERS GROWN ON (0 0 1) GAAS BY MOLECULAR BEAM EPITAXY

X-ray diffraction reciprocal space maps and pole figures were used to analyse the cubic GaN epitaxial layers grown on (0 0 1) GaAs by r.f. plasma source MBE; the presence of hexagonal phase in cubic GaN layers was detected by high resolution x-ray analysis and the relationships among various crystal axes of cubic and hexagonal phase GaN were analysed with respect to V/III source-supply ratio. As for the growth conditions of the epitaxial layers, the V/III ratio was found to drastically affect the quality of the layers. High-temperature growth under near-stoichiometric conditions was necessary to obtain high quality epitaxial layers. It was found that inclusion of the hexagonal phase in the cubic GaN layers could be less than 0.4%, though previously reported typical c-GaN epitaxial layers included as much as 10–20% hexagonal phase GaN. On the basis of the measurements and analyses of reciprocal space maps and pole figures, it was revealed that the orientation of crystal axes of the hexagonal phase was unique in the present GaN epitaxial layers and they were different from those of previously reported c-GaN epitaxial layers.

Hydrothermal synthesis for the preparation of BaTi5O11 fibers

Many of the barium polytitanates have dielectric properties suited for use as ceramic resonators in microwave ®lters. BaTi4O9 and Ba2Ti9O20 are used commercially in the communications industry. The impetus for the preparation of a single-phase BaTi5O11 ceramic is that this material should have a temperature coef®cient of dielectric constant oa close to zero, thus making this ceramic an extremely attractive candidate for use in resonator devices [1]. Synthesis of BaTi5O11 was ®rst reported by Tillmans [2], but single-phase material was not obtained. BaTi5O11 was only obtained metastably from the melt, or was observed as an intermediate reaction product. Until recently, the dielectric properties of BaTi5O11 were reported as relative dielectric constant ar  40 and quality factor Q . 6000 at 9.7 GHz for the sample prepared by an alkoxide solgel method [3]. At present, the conventional preparation methods of single-phase BaTi5O11 powder are the alkoxide sol-gel method and a chemical precipitation method such as citrate route [4]. In this paper, we fabricate BaTi5O11 ®bers for the ®rst time by a hydrothermal synthesis process. There are potential demands for ceramic ®bers to be used for reinforcing ceramics and metal bodies. Moreover, ®brous materials have a number of speci®c properties, such as a highly crystal axis orientation of the grains, a high thermal stability, and so on. With the development of advanced composite material, more attention will be paid to functional ceramic ®bers.

Spiral angle of elementary cellulose fibrils in cell walls ofPicea abies determined by small-angle x-ray scattering

The spiral angle of the elementary cellulose fibril in the wood cell wall, often called microfibril angle, is of primary importance for the mechanical properties of wood. While there are a number of methods to estimate this angle, x-ray diffraction (XRD) techniques have recently obtained a lot of attention because of their ability to provide information averaged over a significantly large specimen volume. Here, we present results from a related method, small-angle x-ray scattering (SAXS). The advantage of SAXS is that, unlike XRD, it does not require any assumption on the orientation of the cellulose crystal axis with respect to the fibril axis. Full three-dimensional scattering patterns were collected using an area detector by rotating the sample around one axis. The distribution of fibrillar orientations was seen to reflect the typical cross-sectional shape of the tracheids (square or circular). In the stem, the spiral angle was found <5° in earlywood and ≈20° in latewood. In branches the angle was ≈30° in the upper part and ≈40° in the lower part, which strongly supports the idea that the spiral angle has primarily mechanical function.

Nonlocal Effects on the Magnetic Penetration Depth ind-Wave Superconductors

We show that, under certain conditions, the low temperature behavior of the magnetic penetration depth $\lambda(T)$ of a pure d-wave superconductor is determined by nonlocal electrodynamics and, contrary to the general belief, the deviation $\Delta\lambda(T) = \lambda(T)-\lambda(0)$ is proportional to T^2 and not T. We predict that the $\Delta\lambda(T)\propto T^2$ dependence, due to nonlocality, should be observable experimentally in nominally clean high-T_c superconductors below a crossover temperature $T^* = (\xi_o/\lambda_o)\Delta_o \sim 1 K$. Possible complications due to impurities, surface quality and crystal axes orientation are discussed.

The influence of Young's modulus on roundness in silicon sphere fabrication [Avogadro constant

Silicon single-crystal spheres for use in accurate determination of the Avogadro constant are fabricated by optical grinding and polishing. Surface profiling of the deviation from sphericity of the spheres shows a strong cubic symmetry on the scale of (20 to 40) mm, which is well correlated with the orientation of the silicon crystal axes and sets a limit on the ultimate shape that can be obtained. This deviation from sphericity can be explained in terms of the variation of Young's modulus with crystal orientation.