Twin-thickness-controlled plastic deformation mechanisms are well understood for submicron-sized twin-structural polycrystalline metals. However, for twin-structural nanocrystalline metals where both ...the grain size and twin thickness reach the nanometre scale, how these metals accommodate plastic deformation remains unclear. Here, we report an integrated grain size and twin thickness effect on the deformation mode of twin-structural nanocrystalline platinum. Above a ∼10 nm grain size, there is a critical value of twin thickness at which the full dislocation intersecting with the twin plane switches to a deformation mode that results in a partial dislocation parallel to the twin planes. This critical twin thickness value varies from ∼6 to 10 nm and is grain size-dependent. For grain sizes between ∼10 to 6 nm, only partial dislocation parallel to twin planes is observed. When the grain size falls below 6 nm, the plasticity switches to grain boundary-mediated plasticity, in contrast with previous studies, suggesting that the plasticity in twin-structural nanocrystalline metals is governed by partial dislocation activities.
Abstract
The resistive switching effect in memristors typically stems from the formation and rupture of localized conductive filament paths, and HfO
2
has been accepted as one of the most promising ...resistive switching materials. However, the dynamic changes in the resistive switching process, including the composition and structure of conductive filaments, and especially the evolution of conductive filament surroundings, remain controversial in HfO
2
-based memristors. Here, the conductive filament system in the amorphous HfO
2
-based memristors with various top electrodes is revealed to be with a quasi-core-shell structure consisting of metallic hexagonal-Hf
6
O and its crystalline surroundings (monoclinic or tetragonal HfO
x
). The phase of the HfO
x
shell varies with the oxygen reservation capability of the top electrode. According to extensive high-resolution transmission electron microscopy observations and ab initio calculations, the phase transition of the conductive filament shell between monoclinic and tetragonal HfO
2
is proposed to depend on the comprehensive effects of Joule heat from the conductive filament current and the concentration of oxygen vacancies. The quasi-core-shell conductive filament system with an intrinsic barrier, which prohibits conductive filament oxidation, ensures the extreme scalability of resistive switching memristors. This study renovates the understanding of the conductive filament evolution in HfO
2
-based memristors and provides potential inspirations to improve oxide memristors for nonvolatile storage-class memory applications.
Tracking the sliding of grain boundaries at the atomic scale Wang, Lihua; Zhang, Yin; Zeng, Zhi ...
Science (American Association for the Advancement of Science),
2022-Mar-18, 2022-03-18, 20220318, Letnik:
375, Številka:
6586
Journal Article
Recenzirano
Grain boundaries (GBs) play an important role in the mechanical behavior of polycrystalline materials. Despite decades of investigation, the atomic-scale dynamic processes of GB deformation remain ...elusive, particularly for the GBs in polycrystals, which are commonly of the asymmetric and general type. We conducted an in situ atomic-resolution study to reveal how sliding-dominant deformation is accomplished at general tilt GBs in platinum bicrystals. We observed either direct atomic-scale sliding along the GB or sliding with atom transfer across the boundary plane. The latter sliding process was mediated by movements of disconnections that enabled the transport of GB atoms, leading to a previously unrecognized mode of coupled GB sliding and atomic plane transfer. These results enable an atomic-scale understanding of how general GBs slide in polycrystalline materials.
Pt-based magnetic nanocatalysts are one of the most suitable candidates for electrocatalytic materials due to their high electrochemistry activity and retrievability. Unfortunately, the inferior ...durability prevents them from being scaled-up, limiting their commercial applications. Herein, an antiferromagnetic element Mn was introduced into PtCo nanostructured alloy to synthesize uniform Mn-PtCo truncated octahedral nanoparticles (TONPs) by one-pot method. Our results show that Mn can tune the blocking temperature of Mn-PtCo TONPs due to its antiferromagnetism. At low temperatures, Mn-PtCo TONPs are ferromagnetic, and the coercivity increases gradually with increasing Mn contents. At room temperature, the Mn-PtCo TONPs display superparamagnetic behavior, which is greatly helpful for industrial recycling. Mn doping can not only modify the electronic structure of PtCo TONPs but also enhance electrocatalytic performance for methanol oxidation reaction. The maximum specific activity of Mn-PtCo-3 reaches 8.1 A·m
-2
, 3.6 times of commercial Pt/C (2.2 A·m
-2
) and 1.4 times of PtCo TONPs (5.6 A·m
-2
), respectively. The mass activity decreases by only 30% after 2,000 cycles, while it is 45% and 99% (nearly inactive) for PtCo TONPs and commercial Pt/C catalysts, respectively.
Detwinning is an important plastic deformation mechanism that can significantly affect the mechanical properties of twin-structured metals. Although many detwinning mechanisms have been proposed for ...pure metals, it is unclear whether such a deformation model is valid for nanocrystalline alloys because of the lack of direct evidence. Here, the atomicscale detwinning deformation process of a nanocrystalline AuAg alloy with an average grain size of ∼15 nm was investigated
in situ
. The results show that there are three types of detwinning mechanisms in nanocrystalline AuAg alloys. The first type of detwinning results from grain boundary migration. The second type of detwinning occurs through combined layer-by-layer thinning and incoherent twin boundary migration. The last one occurs through incoherent twin boundary migration, which results from the collective motion of partial dislocations in an array.
The deformation mechanisms of twin-structured metallic materials have attracted great interest. Though previous theoretical predictions have suggested that the repulsive force of the twin boundary ...(TB) can significantly affect the deformation of twin-structured metals, it remains unclear whether this prediction applies to experimental conditions. In this paper, the atomic-scaled deformation process of twin-structured Pt nanocrystals was
in situ
observed using our home-made device in a high-resolution transmission electron microscope. We have shown that the plastic deformation of the twin-structured Pt nanocrystals was governed by full dislocation generation as well as Lomer dislocation (LD) lock formation and destruction. After LD locks were destructed, these full dislocations tended to move towards the surface of the nanocrystals. The findings revealed that due to the ultra-high repulsive force of TB on dislocation, there was no dislocation-TB reaction during the deformation. These findings can enrich our understanding of the dislocation behaviors of twin-structured nanocrystals.
In situ atomic-scale bending tests of twin-structured Ni nanowires were realised using a homemade deformation device. The results showed that the plastic deformation mechanism in twin-structured Ni ...nanowires depended on the deformation stage. At the early stages of bending deformation, the plasticity of twin-structured Ni nanowires was controlled by dislocations interacting with the twin boundaries or parallel to them. With increasing bending strain, both dislocation and face-centred cubic–body-centred tetragonal phase transition occurred. At very high bending strain, grain boundaries resulting from the lattice distortion/collapse were formed. This study details the deformation mechanisms of the twin-structured Ni nanowires under bending deformation, which advances the basic understanding of the plasticity mechanisms in metals.
Incoherent-twin boundaries (ITBs) can significantly affect the mechanical properties exhibited by metals. Although numerous studies have been conducted to date, the atomic structures of such ITBs ...remain unclear, owing to difficulties in imaging their structure. In this study, high-angle annular dark-field imaging was used to reveal the atomic structure of the ITBs present in Pt. We discovered that both the twin thickness and the dislocation-ITB interaction can affect the ITB phase structure. In thin twins, the {111} planes between the ITB remain flat without any obvious displacement along the direction, whereas in thicker twins, the {111} planes between the ITB exhibit clear displacement along the direction, with this displacement increasing as the twin thickness increases. The ITBs frequently absorb full dislocations, which leads to the formation of dislocation-misaligned ITBs. This twin-thickness effect and dislocation-ITB interaction, which resulted ITB-phase variation, has rarely been reported.
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•Atomic-scale results reveal that the structure of ITB is twin-thickness dependent•The twin thickness can affect the alignment of the {111} planes between ITBs•The interaction between the dislocation and the ITB leads to an ITB phase transition
Previous classic theoretical models have predicted that the {111} planes between the incoherent-twin boundary (ITB) should remain flat without displacement along the direction. In this research article, Guo et al. show atomic-scale evidence of the twin-thickness effect on the ITB phase transition and the displacement along the direction.
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