227 research outputs found
Derived Crystal Structure of Martensitic Materials by Solid-Solid Phase Transformation
We propose a mathematical description of crystal structure: underlying
translational periodicity together with the distinct atomic positions up to the
symmetry operations in the unit cell. It is consistent with the international
table of crystallography. By the Cauchy-Born hypothesis, such a description can
be integrated with the theory of continuum mechanics to calculate a derived
crystal structure produced by solid-solid phase transformation. In addition, we
generalize the expressions for orientation relationship between the parent
lattice and the derived lattice. The derived structure rationalizes the lattice
parameters and the general equivalent atomic positions that assist the indexing
process of X-ray diffraction analysis for low symmetry martensitic materials
undergoing phase transformation. The analysis is demonstrated in a CuAlMn shape
memory alloy. From its austenite phase (L2_1 face-centered cubic structure), we
identify that the derived martensitic structure has the orthorhombic symmetry
Pmmm with derived lattice parameters a_dv = 4.36491 \AA, b_dv = 5.40865 \AA and
c_dv = 4.2402 \AA, by which the complicated X-ray Laue diffraction pattern can
be well indexed, and the orientation relationship can be verified.Comment: 20 pages, 5 figure
Internal stresses in pre-stressed micron-scale aluminum core-shell particles and their improved reactivity
Dilatation of aluminum (Al) core for micron-scale particles covered by alumina (Al2O3) shell was measured utilizing x-ray diffraction with synchrotron radiation for untreated particles and particles after annealing at 573 K and fast quenching at 0.46 K/s. Such a treatment led to the increase in flame rate for Al + CuO composite by 32% and is consistent with theoretical predictions based on the melt-dispersion mechanism of reaction for Al particles. Experimental results confirmed theoretical estimates and proved that the improvement of Al reactivity is due to internal stresses. This opens new ways of controlling particle reactivity through creating and monitoring internal stresses
Energy conversion from heat to electricity by highly reversible phase-transforming ferroelectrics
Searching for performant multiferroic materials attracts general research
interests in energy science as they have been increasingly exploited as the
conversion media among thermal, electric, magnetic and mechanical energies by
using their temperature-dependent ferroic properties. Here we report a material
development strategy that guides us to discover a reversible phase-transforming
ferroelectric material exhibiting enduring energy harvesting from small
temperature differences. The material satisfies the crystallographic
compatibility condition between polar and nonpolar phases, which shows only
2.5C thermal hysteresis and high figure of merit. It stably generates 15uA
electricity in consecutive thermodynamic cycles in absence of any bias fields.
We demonstrate our device to consistently generate 6uA/cm2 current density near
100C over 540 complete phase transformation cycles without any electric and
functional degradation. The energy conversion device can light up a LED
directly without attaching an external power source. This promising material
candidate brings the low-grade waste heat harvesting closer to a practical
realization, e.g. small temperature fluctuations around the water boiling point
can be considered as a clean energy source.Comment: 21 pages, 9 figures, 2 table
Impact ignition and combustion of micron-scale aluminum particles pre-stressed with different quenching rates
Pre-stressing aluminum (Al) particles by annealing and quenching alters dilatational strain and is linked to increased particle reactivity. The quenching rate associated with pre-stressing is a key parameter affecting the final stress state within the Al particle, with faster quenching rates theoretically favoring a higher, more desirable stress state. Micron scale Al particles are annealed to 573 K, then quenched at different rates (i.e., 200 and 900 K/min), mixed with bismuth oxide (Bi2O3), and the Al + Bi2O3 mixtures are examined under low-velocity, drop-weight impact conditions. Both quenching rates showed increased impact ignition sensitivity (i.e., between 83% and 89% decrease in ignition energy). However, the slower quenching rate showed a 100% increase in pressurization rate compared to untreated particles, while the faster quenching rate showed a 97% increase in peak pressure, indicating that these two quenching rates affect Al particles differently. Surprisingly, synchrotron X-ray diffraction data show that the 200 K/min quenched particles have a higher dilatational strain than the untreated particles or the 900 K/min quenched particles. Results are rationalized with the help of a simple mechanical model that takes into account elastic stresses, creep in the alumina shell, and delamination of shell from the core. The model predicts that Al powder quenched at 200 K/min did not experience delamination. In contrast, Al quenched at 900 K/min did not have creep but does have delamination, and under impact, delamination led to major fracture, greater oxygen access to the core, and significant promotion of reaction. Thus, the increase in quenching rate and shell-core delamination are more important for the increase in Al reactivity than pre-stressing alone
Data-driven approach for synchrotron X-ray Laue microdiffraction scan analysis
We propose a novel data-driven approach for analyzing synchrotron Laue X-ray
microdiffraction scans based on machine learning algorithms. The basic
architecture and major components of the method are formulated mathematically.
We demonstrate it through typical examples including polycrystalline BaTiO,
multiphase transforming alloys and finely twinned martensite. The computational
pipeline is implemented for beamline 12.3.2 at the Advanced Light Source,
Lawrence Berkeley National Lab. The conventional analytical pathway for X-ray
diffraction scans is based on a slow pattern by pattern crystal indexing
process. This work provides a new way for analyzing X-ray diffraction 2D
patterns, independent of the indexing process, and motivates further studies of
X-ray diffraction patterns from the machine learning prospective for the
development of suitable feature extraction, clustering and labeling algorithms.Comment: 29 pages, 25 figures under the second round of review by Acta
Crystallographica
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Scalable Freeze-Tape-Casting Fabrication and Pore Structure Analysis of 3D LLZO Solid-State Electrolytes.
Nonflammable solid-state electrolytes can potentially address the reliability and energy density limitations of lithium-ion batteries. Garnet-structured oxides such as Li7La3Zr2O12 (LLZO) are some of the most promising candidates for solid-state devices. Here, three-dimensional (3D) solid-state LLZO frameworks with low tortuosity pore channels are proposed as scaffolds, into which active materials and other components can be infiltrated to make composite electrodes for solid-state batteries. To make the scaffolds, we employed aqueous freeze tape casting (FTC), a scalable and environmentally friendly method to produce porous LLZO structures. Using synchrotron radiation hard X-ray microcomputed tomography, we confirmed that LLZO films with porosities of up to 75% were successfully fabricated from slurries with a relatively wide concentration range. The acicular pore size and shape at different depths of scaffolds were quantified by fitting the pore shapes with ellipses, determining the long and short axes and their ratios, and investigating the equivalent diameter distribution. The results show that relatively homogeneous pore sizes and shapes were sustained over a long range along the thickness of the scaffold. Additionally, these pores had low tortuosity and the wall thickness distributions were found to be highly homogeneous. These are desirable characteristics for 3D solid electrolytes for composite electrodes, in terms of both the ease of active material infiltration and also minimization of Li diffusion distances in electrodes. The advantages of the FTC scaffolds are demonstrated by the improved conductivity of LLZO scaffolds infiltrated with poly(ethylene oxide)/lithium bis(trifluoromethanesulfonyl)imide (PEO/LITFSI) compared to those of PEO/LiTFSI films alone or composites containing LLZO particles
Resistive contribution in electrical switching experiments with antiferromagnets
Recent research demonstrated the electrical switching of antiferromagnets via
intrinsic spin-orbit torque or the spin Hall effect of an adjacent heavy metal
layer. The electrical readout is typically realized by measuring the transverse
anisotropic magnetoresistance at planar cross- or star-shaped devices with four
or eight arms, respectively. Depending on the material, the current density
necessary to switch the magnetic state can be large, often close to the
destruction threshold of the device. We demonstrate that the resulting
electrical stress changes the film resistivity locally and thereby breaks the
fourfold rotational symmetry of the conductor. This symmetry breaking due to
film inhomogeneity produces signals, that resemble the anisotropic
magnetoresistance and is experimentally seen as a "saw-tooth"-shaped transverse
resistivity. This artifact can persist over many repeats of the switching
experiment and is not easily separable from the magnetic contribution. We
discuss the origin of the artifact, elucidate the role of the film
crystallinity, and propose approaches how to separate the resistive
contribution from the magnetic contribution.Comment: 9 pages, 7 figure
Resistive contribution in electrical switching experiments with antiferromagnets
Recent research demonstrated the electrical switching of antiferromagnets via
intrinsic spin-orbit torque or the spin Hall effect of an adjacent heavy metal
layer. The electrical readout is typically realized by measuring the transverse
anisotropic magnetoresistance at planar cross- or star-shaped devices with four
or eight arms, respectively. Depending on the material, the current density
necessary to switch the magnetic state can be large, often close to the
destruction threshold of the device. We demonstrate that the resulting
electrical stress changes the film resistivity locally and thereby breaks the
fourfold rotational symmetry of the conductor. This symmetry breaking due to
film inhomogeneity produces signals, that resemble the anisotropic
magnetoresistance and is experimentally seen as a "saw-tooth"-shaped transverse
resistivity. This artifact can persist over many repeats of the switching
experiment and is not easily separable from the magnetic contribution. We
discuss the origin of the artifact, elucidate the role of the film
crystallinity, and propose approaches how to separate the resistive
contribution from the magnetic contribution.Comment: 9 pages, 7 figure
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