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Diffusionless transformation of soft cubic superstructure from amorphous to simple cubic and body-centered cubic phases.

ABSTRACT: In a narrow temperature window in going from the isotropic to highly chiral orders, cholesteric liquid crystals exhibit so-called blue phases, consisting of different morphologies of long, space-filling double twisted cylinders. Those of cubic spatial symmetry have attracted considerable attention in recent years as templates for soft photonic materials. The latter often requires the creation of monodomains of predefined orientation and size, but their engineering is complicated by a lack of comprehensive understanding of how blue phases nucleate and transform into each other at a submicrometer length scale. In this work, we accomplish this by intercepting nucleation processes at intermediate stages with fast cross-linking of a stabilizing polymer matrix. We reveal using transmission electron microscopy, synchrotron small-angle X-ray diffraction, and angle-resolved microspectroscopy that the grid of double-twisted cylinders undergoes highly coordinated, diffusionless transformations. In light of our findings, the implementation of several applications is discussed, such as temperature-switchable QR codes, micro-area lasing, and fabrication of blue phase liquid crystals with large domain sizes.

SUBMITTER: Liu J

PROVIDER: S-EPMC8190294 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Hydrogenation treatment under several gigapascals assists diffusionless transformation in a face-centered cubic steel.

Project description:The use of hydrogen in iron and steel has the potential to improve mechanical properties via altering the phase stability and dislocation behavior. When hydrogen is introduced under several gigapascals, a stoichiometric composition of hydrogen can be introduced for steel compositions. In this study, a face-centered cubic (fcc) stainless steel was hydrogenated under several gigapascals. When the steel was not hydrogenated, the microstructure after depressurization was an fcc with a hexagonal close-packed (hcp) structure. In contrast, the hydrogenation treatment resulted in a fine lath body-centered cubic (bcc) structure arising from diffusionless transformation. In particular, the bcc phase formed through the following transformation sequence: fcc → hcp → dhcp (double hexagonal close-packed phase) → bcc. That is, the use of hydrogenation treatment realized fine microstructure evolution through a new type of diffusionless transformation sequence, which is expected to be used in future alloy design strategies for developing high-strength steels.

| S-EPMC8481468 | biostudies-literature

Unstable twin in body-centered cubic tungsten nanocrystals.

Project description:Twinning is commonly activated in plastic deformation of low stacking-fault face-centered cubic (Fcc) metals but rarely found in body-centered cubic (Bcc) metals under room temperature and slow strain rates. Here, by conducting in situ transmission electron microscopy (TEM) at atomic scale, we discover that, in stark contrast to those in most Fcc metals, a majority of deformation twins in Bcc metals are unstable and undergo spontaneously detwinning upon unloading. Such unexpected instability of Bcc twins is found to be closely related to the prevalence of the inclined twin boundaries-a peculiar structure where twin boundaries are not parallel to the twinning plane, and the degree of instability is in direct proportion to the fraction of the inclined twin boundary. This work provides significant insights into the structure and stability of deformation twins in Bcc metals.

| S-EPMC7237484 | biostudies-literature

Reversible nanocluster structure transformation between face-centered cubic and icosahedral isomers.

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Enhanced Low-temperature Electro-optical Kerr Effect of Stable Cubic Soft Superstructure Enabled by Fluorinated Polymer Stabilization.

Project description:An enhanced electro-optical Kerr effect of the stable self-organized cubic blue phase liquid crystal superstructure at a relatively low temperature down to -50?°C was achieved through a judiciously designed fluorinated polymer stabilization. The fluorinated sample exhibited not only a rather stable cubic structure, but the promoted electro-optical performances of low driving voltage, weak hysteresis and high contrast ratio at such a low-temperature, which were much distinct from the common non-fluorinated polymer stabilized blue phase liquid crystal without conspicuous low-temperature Kerr response behaviours. Kerr constant, which reflects the obviousness of Kerr effect, of the fluorinated sample at -50?°C indicated a spectacular enhancement of two orders of magnitude in contrast to the commonly material, thereby corroborating the high efficiency of polymer fluorination in enhancing low-temperature Kerr effect. Such an enhancement of Kerr effect was probably resulted from the decreasing of interfacial anchoring between liquid crystal and fluorinated polymer network. The fluorinated polymer stabilization not only ensures the stability of self-organized cubic structure of blue phase, but overcomes the challenge and bottleneck problem of low-temperature inapplicability of common blue phase liquid crystal and paves a brilliant and broad way for relevant materials to abundant perspective applications at low temperature.

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Consecutive crystallographic reorientations and superplasticity in body-centered cubic niobium nanowires.

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| S-EPMC6035040 | biostudies-literature

Singular orientations and faceted motion of dislocations in body-centered cubic crystals.

Project description:Dislocation mobility is a fundamental material property that controls strength and ductility of crystals. An important measure of dislocation mobility is its Peierls stress, i.e., the minimal stress required to move a dislocation at zero temperature. Here we report that, in the body-centered cubic metal tantalum, the Peierls stress as a function of dislocation orientation exhibits fine structure with several singular orientations of high Peierls stress-stress spikes-surrounded by vicinal plateau regions. While the classical Peierls-Nabarro model captures the high Peierls stress of singular orientations, an extension that allows dislocations to bend is necessary to account for the plateau regions. Our results clarify the notion of dislocation kinks as meaningful only for orientations within the plateau regions vicinal to the Peierls stress spikes. These observations lead us to propose a Read-Shockley type classification of dislocation orientations into three distinct classes-special, vicinal, and general-with respect to their Peierls stress and motion mechanisms. We predict that dislocation loops expanding under stress at sufficiently low temperatures, should develop well defined facets corresponding to two special orientations of highest Peierls stress, the screw and the M111 orientations, both moving by kink mechanism. We propose that both the screw and the M111 dislocations are jointly responsible for the yield behavior of BCC metals at low temperatures.

| S-EPMC3458394 | biostudies-literature

Discrete shear band plasticity through dislocation activities in body-centered cubic tungsten nanowires.

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| S-EPMC5854623 | biostudies-literature

Unusual activated processes controlling dislocation motion in body-centered-cubic high-entropy alloys.

Project description:Atomistic simulations of dislocation mobility reveal that body-centered cubic (BCC) high-entropy alloys (HEAs) are distinctly different from traditional BCC metals. HEAs are concentrated solutions in which composition fluctuation is almost inevitable. The resultant inhomogeneities, while locally promoting kink nucleation on screw dislocations, trap them against propagation with an appreciable energy barrier, replacing kink nucleation as the rate-limiting mechanism. Edge dislocations encounter a similar activated process of nanoscale segment detrapping, with comparable activation barrier. As a result, the mobility of edge dislocations, and hence their contribution to strength, becomes comparable to screw dislocations.

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Spontaneous mirror symmetry breaking in benzil-based soft crystalline, cubic liquid crystalline and isotropic liquid phases.

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Stability and equation of state of face-centered cubic and hexagonal close packed phases of argon under pressure.

Project description:The compression of argon is measured between 10 K and 296 K up to 20 GPa and and up to 114 GPa at 296 K in diamond anvil cells. Three samples conditioning are used: (1) single crystal sample directly compressed between the anvils, (2) powder sample directly compressed between the anvils, (3) single crystal sample compressed in a pressure medium. A partial transformation of the face-centered cubic (fcc) phase to a hexagonal close-packed (hcp) structure is observed above 4.2-13 GPa. Hcp phase forms through stacking faults in fcc-Ar and its amount depends on pressurizing conditions and starting fcc-Ar microstructure. The quasi-hydrostatic equation of state of the fcc phase is well described by a quasi-harmonic Mie-Grüneisen-Debye formalism, with the following 0 K parameters for Rydberg-Vinet equation: [Formula: see text] = 38.0 Å[Formula: see text]/at, [Formula: see text] = 2.65 GPa, [Formula: see text] = 7.423. Under the current experimental conditions, non-hydrostaticity affects measured P-V points mostly at moderate pressure ([Formula: see text] 20 GPa).

| S-EPMC8313556 | biostudies-literature

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