Function Of Crystalline Orientation Research Articles

The role of orientation on the shock response of single crystal tantalum

The response of single crystalline tantalum to one-dimensional shock loading has been investigated as a function of crystalline orientation to the loading axis. Results show that this has a significant effect, particularly on the Hugoniot elastic limit (HEL). [100] and [111] HELs are near identical with the [110] HEL having the lowest strength. This is contrary to predictions obtained by applying the Schmid factor analysis, where the ordering was expected to be (highest strength first) [111], [110], with the [100] orientation being the softest. Adopting a more appropriate model based on uniaxial strain conditions, as was previously done successfully for FCC aluminum and copper, did not rationalize our observations. We show that a non-Schmid effective stress model, incorporating twinning/anti-twinning asymmetry, has much greater success in reproducing the experimental relative HELs magnitudes. Using this model, we make a quantitative estimation of the magnitude of non-Schmid effects and compare these to equivalent low temperature, quasi-static estimates from the literature.

Revealing Anisotropic Spinel Formation on Pristine Li‐ and Mn‐Rich Layered Oxide Surface and Its Impact on Cathode Performance

Surface properties of cathode particles play important roles in the transport of ions and electrons and they may ultimately dominate cathode's performance and stability in lithium‐ion batteries. Through the use of carefully prepared Li1.2Ni0.13Mn0.54Co0.13O2 crystal samples with six distinct morphologies, surface transition‐metal redox activities and crystal structural transformation are investigated as a function of surface area and surface crystalline orientation. Complementary depth‐profiled core‐level spectroscopy, namely, X‐ray absorption spectroscopy, electron energy loss spectroscopy, and atomic‐resolution scanning transmission electron microscopy, are applied in the study, presenting a fine example of combining advanced diagnostic techniques with a well‐defined model system of battery materials. The present study reports the following findings: (1) a thin layer of defective spinel with reduced transition metals, similar to what is reported on cycled conventional secondary particles in the literature, is found on pristine oxide surface even before cycling, and (2) surface crystal structure and chemical composition of both pristine and cycled particles are facet dependent. Oxide structural and cycling stabilities improve with maximum expression of surface facets stable against transition‐metal reduction. The intricate relationships among morphology, surface reactivity and structural transformation, electrochemical performance, and stability of the cathode materials are revealed.

Interfacial Studies of the SEI Layer on a Tin Electrode

Development of new innovative experimental approaches and enabling methodologies to understand the function and mechanism of operation of materials, electrodes and electrochemical interfaces in electrical energy storage systems is critical for clean and/or renewable energy technologies. A better understanding of the underlying principles that govern these phenomena is inextricably linked with successful implementation of high energy density materials.Several analytical techniques have been implemented for the physico-chemical characterization of the materials, interfaces and interphases. In many cases limitations in studying the real system are imposed by ex situ methods that require excitation or detection of electrons or ions in vacuum environment and/or they suffer from inadequate sensitivity, selectivity and specificity in the in situ environment. The advent of near-field optical methods during the past decades has led to the development of new advanced techniques for chemical analysis. This presentation provides a brief overview of novel in and ex situexperimental approaches aimed at probing battery materials and electrodes in electrical storage systems at an atom, molecular or nanoparticulate level.A strong understanding of the solid electrolyte interphase (SEI) (1,2) layer in lithium-ion batteries is necessary for further development of the technology, leading the path to application of high energy density intermetallic anodes However, the identification of chemical compounds in this surface layer, as well as their spatial distribution, has been limited by diffraction to the 5-10 μm wavelength scale available to traditional Fourier Transform Infrared spectroscopy (FTIR). This study demonstrates subwavelength imaging of the SEI using infrared (IR) near-field scanning optical microscopy (NSOM). NSOM (3) is a technique based on light confinement at the apex of an atomic force microscope (AFM) probe. The tight optical focusing combined with the placement of the probe within small fractions of a wavelength allow resolution well below the classical diffraction limit, while simultaneously obtaining topographic information about the sample surface and the present SEI. Additionally, this microscope is highly surface-sensitive, allowing selective optical imaging of the interfacial layers. The NSOM used here is configured as part of a pseudo-heterodyne interferometer, which allows high signal-to-noise ratio as well as collection of the optical phase.The observed significant difference of Sn reactivity toward the electrolyte as a function of Sn surface crystalline orientation suggests radically different reaction paths, reduction products, and properties of the surface film. These results were supported by reactivity of polycrystalline tin that was falling in between the two single crystal surfaces. Our most recent measurements however shed new light on these results. We have identified that the native oxide layer present on tin exposed to air, and appreciable oxygen solubility in Sn have a major contribution to the electrochemical response of the Sn electrode. The presented experimental methodologies exploit the micro and nano-manipulation techniques and Sn single crystal model electrodes to provide sufficient sample definition suitable for advanced X-ray, far- and near-field Raman, FTIR and electrochemical characterization techniques. Examples of detailed in situmolecular characterization of electrode surface and bulk processes at the nano-level scale limit will be discussed. These include elemental and molecular depth profiling at nanometer-scale depth resolution of a solid electrolyte interface (SEI) layer formed on Sn polycrystalline and monocrystral model electrodes in an organic carbonate-based electrolyte.AcknowledgementPart of this work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy, under contract no. DE-AC02-05CH11231. It has also been supported in part by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DESC0001294. This work was also supported in part by the Chemical Science Division, Office of Basic Energy Sciences, Office of Nuclear Nonproliferation, and the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

BiFeO3/La0.7Sr0.3MnO3 heterostructures deposited on spark plasma sintered LaAlO3 substrates

Multiferroic BiFeO3 (BFO)/La0.7Sr0.3MnO3 heterostructured thin films were grown by pulsed laser deposition on polished spark plasma sintered LaAlO3 (LAO) polycrystalline substrates. Both polycrystalline LAO substrates and BFO films were locally characterized using electron backscattering diffraction, which confirmed the high-quality local epitaxial growth on each substrate grain. Piezoforce microscopy was used to image and switch the piezo-domains, and the results are consistent with the relative orientation of the ferroelectric variants with the surface normal. This high-throughput synthesis process opens the routes towards wide survey of electronic properties as a function of crystalline orientation in complex oxide thin film synthesis.

Interfacial processes at single-crystal β-Sn electrodes in organic carbonate electrolytes

In situ atomic force microscopy (AFM) and spectroscopic ellipsometry were used to study the mechanism of organic carbonate electrolytes decomposition and surface layer (re)formation at β-Sn(001) and (100) single crystal electrodes. Interfacial phenomena were investigated at potentials above 0.8 V vs. Li/Li +, i.e. where no Sn–Li alloying takes place. The Sn(001) electrode tends to form a protective surface layer of electrolyte reduction products during the first cathodic CV scan, which effectively inhibits further reduction of the electrolyte upon cycling. In contrast, the Sn(100) electrode produces a thick, inhomogeneous and unstable surface layer. The observed significant difference of Sn reactivity toward the electrolyte as a function of Sn surface crystalline orientation suggests radically different reaction paths, reduction products, and properties of the surface film.

Deformation Substructures and Their Transitions in Laser Shock–Compressed Copper-Aluminum Alloys

It is shown that the short pulse durations (0.1 to 10 ns) in laser shock compression ensure a rapid decay of the pulse and quenching of the shocked sample in times that are orders of magnitude lower than in conventional explosively driven plate impact experiments. Thus, laser compression, by virtue of a much more rapid cooling, enables the retention of a deformation structure closer to the one existing during shock. The smaller pulse length also decreases the propensity for localization. Copper and copper aluminum (2 and 6 wt pct Al) with orientations [001] and $$ [\ifmmode\expandafter\bar\else\expandafter\=\fi{1}34] $$ were subjected to high intensity laser pulses with energy levels of 70 to 300 J delivered in an initial pulse duration of approximately 3 ns. The [001] and $$ [\ifmmode\expandafter\bar\else\expandafter\=\fi{1}34] $$ orientations were chosen, because they respectively maximize and minimize the number of slip systems with highest resolved shear stresses. Systematic differences of the defect substructure were observed as a function of pressure, stacking-fault energy, and crystalline orientation. The changes in the mechanical properties for each condition were compared using micro- and nanohardness measurements and correlated well with observations of the defect substructure. Three regimes of plastic deformation were identified and their transitions modeled: dislocation cells, stacking faults, and twins. An existing constitutive description of the slip to twinning transition, based on the critical shear stress, was expanded to incorporate the effect of stacking-fault energy. A new physically based criterion accounting for stacking-fault energy was developed that describes the transition from perfect loop to partial loop homogeneous nucleation, and consequently from cells to stacking faults. These calculations predict transitions that are in qualitative agreement with the effect of SFE.

A Study of Shock-Wave Propagation in Single Crystallinefcc-Al and α-Fe2O3and an Interface between Two Such Phases Using MD Simulations

AbstractThis research focuses on shock wave propagation in <100>, <110>, and <111> oriented single crystalline Al, <0001> oriented single crystalline Fe2O3, and an interface between the {100} surface of Al and the {0001} surface of Fe2O3. An interatomic potential is developed to describe interatomic interactions in the Fe+Al+Fe2O3+Al2O3material system. The potential is capable of describing the behaviors of Fe, Al, Fe2O3, and Al2O3as well as of composites consisting of any combination of these components. The analyses in single crystals focus on the relationships between the shock wave velocity (US) and the particle velocity (UP) as a function of single crystalline orientation. Calculations also focus on the formation and propagation of defects. The analyses reveal that the US-UPrelationship as well as the type and the extent of deformation strongly depend on the crystallographic orientation. The interfacial shock wave propagation analyses focus on the change in atomic structure near the interface as a function of UP. Calculations show that there is a threshold UPvalue above which the atomic structure on both sides of the interface undergoes significant changes which are accompanies by enhanced increase in temperature and pressure relative to what is seen in both phases when they are deformed alone. This observation suggests a possibility that this threshold may represent the onset of a shock-induced reactive structural change.

Doubly rotated contoured quartz resonators.

Doubly rotated contoured quartz resonators are used in the design of temperature-compensated stable clocks and dual-mode sensors for simultaneous measurements of pressure and temperature. The design of these devices is facilitated by models that can predict frequency spectra associated with the three thickness modes and temperature and stress-induced frequency changes as a function of crystalline orientation. The Stevens-Tiersten technique for the analysis of the C-mode of a doubly rotated contoured quartz resonator is extended to include the other two thickness modes. Computational results for harmonic and anharmonic overtones of all three thickness modes of such resonators help in optimizing the radius of curvature of the contour and electrode shape for suppression of unwanted modes and prevention of activity dips. The temperature and stress-induced changes in thickness-mode resonator frequencies are calculated from a perturbation technique for small dynamic fields superposed on a static bias. The static bias refers to either a temperature or stress-induced static deformation of the resonator plate. Phenomenological models are also used for calculating the temperature and stress-induced changes in resonant frequencies as a function of crystalline orientation. Results for the SBTC-cut quartz plate with a spherical convex contour of 260 mm indicate that normal trapping occurs for the third (n = 3) and fifth (n = 5) harmonic of the A-mode, the fundamental (n = 1) and third (n = 3) harmonic of the B-mode, and the fundamental (n = 1) and fifth (n = 5) harmonic of the C-mode.

Brillouin scattering in Li2SO4: Liquid and plastic crystalline phases

Abstract The hypersonic velocity in Li 2 SO 4 was measured through the liquid-plastic transition for an arbitrary crystalline orientation. The velocity showed a sharp discontinuity at the phase transition. The phonon frequency was a periodic function of crystalline orientation.

Size effects and the anisotropy of the electron relaxation processes in single crystal films of gallium at low temperatures

The variation of electrical resistivity of thin rectangular, single crystal films of 99.9999% gallium has been investigated from 1.1° to 20°K, as a function of crystalline orientation, for thicknesses between 40 and 250 µ. As long as the ratio of the thickness to the average bulk mean free path ≪1, the ideal resistivity is proportional to a power which depends on the orientation of the film and which varies betweenT 3 andT 1.5 . It is argued that the strongT 2 term, found in the bulk resistivity at low temperatures, is not a consequence of electron-electron collisions, but is caused by an averaging, over the entire Fermi surface, of temperature dependences which are different for different regions because of Umklapp scattering. For the thinnest specimens size effects are appreciable up to 15°K, but there is both quantitative and qualitative disagreement between our results and the theoretical calculations of Fuchs, which are for an idealized metal. Attempts are made to show that a change in the nature of the bulk scattering mechanisms can be deduced by comparing our data with Fuch's predictions.

Orientation Dependence of Ultrasonic Attenuation in Copper

The ultrasonic attenuation of longitudinal phonons in copper single crystals has been measured in a temperature range from 2 to 80\ifmmode^\circ\else\textdegree\fi{}K, and in a frequency range from 8 to 72 Mc/sec; these measurements cover a range in $\mathrm{ql}$ from 0.07 to 4.0. Analysis of these results shows that for values of $\mathrm{ql}\ensuremath{\gg}1$, the attenuation associated with the electron-phonon interaction is a function of crystalline orientation. For values of $\mathrm{ql}\ensuremath{\ll}1$, the attenuation is found to be independent of crystalline orientation, and in good agreement with a free-electron model. The attenuation associated with the dislocation-phonon interaction is also found to be orientation-dependent. Calculations in which the deviations of the real Fermi surface from a free-electron sphere are considered do not account fully for the anisotropic behavior of the attenuation; hence one concludes that the deformation of the Fermi surface as a function of the direction and polarization of the imposed phonons must be the significant quantity.

Internal friction and transmission electron microscopy studies of magnesium—I. Internal friction

The internal friction of Mg was studied at 4 kc/s and 40 kc/s as a function of temperature (4.2–300°K), plastic deformation, crystalline orientation, heat treatment and impurity content. In pre-strained polycrystalline samples a peak was observed at 20°K which annealed out readily at 300°K, and a very broad peak between 40 and 240°K which showed a complex dependence on deformation and annealing. In deformed single crystals only the broad peak was found. The variation with orientation indicates that the peak is caused by dislocation motion in the (0001 ) slip system. The annealing behavior points to a possible dissociation of non-basal dislocations into basal and non-basal components. Addition of 1% Li suppressed both peaks, while Ni and Fe (which form precipitates) enhanced them.

Optimum orientation for yttrium-iron-garnet spheres for eliminating anisotropy effects

A general expression for the frequency of ferromagnetic resonance as a function of crystalline orientation is developed. From this, an analytical expression is derived, giving the orientations of a y.i.g. sphere where the resonance frequency is unaffected by changes in anisotropy constant. It is shown that, for practical device applications, orientation of samples along a [0, 8, 13] axis provides the least sensitivity to misalignment.