Electrode materials viewed with transmission electron microscopy

Orlova, Elena D.; Morozov, Anatolii V.; Abakumov, Artem M.

doi:10.1016/b978-0-12-823144-9.00031-5

Cited by 2 publications

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“…40 The capabilities of dDPC-STEM imaging to retrieve the positions of both "heavy" and "light" elements in Li-ion battery cathodes at very low electron irradiation dose have already been demonstrated. 5,41 Compared to HAADF-STEM images, the dDPC-STEM images demonstrate an inverted contrast, that is, the areas of higher projected electrostatic potential appear darker. In the [010] R dDPC-STEM image of Li 2+x Mo 1−x O 3 (Figure 10a), the darkest dots correspond to projections of the Li/Mo columns.…”

Section: ■ Introductionmentioning

confidence: 99%

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions

et al. 2022

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A broad range of cationic nonstoichiometry has been demonstrated for the Li-rich layered rock-salt-type oxide Li 2 MoO 3 , which has generally been considered as a phase with a well-defined chemical composition. Li 2+x Mo 1−x O 3 (−0.037 ≤ x ≤ 0.124) solid solutions were synthesized via hydrogen reduction of Li 2 MoO 4 in the temperature range of 650−1100 °C, with x decreasing with the increase of the reduction temperature. The solid solutions adopt a monoclinically distorted O3-type layered average structure and demonstrate a robust local ordering of the Li cations and Mo 3 triangular clusters within the mixed Li/Mo cationic layers. The local structure was scrutinized in detail by electron diffraction and aberration-corrected scanning transmission electron microcopy (STEM), resulting in an ordering model comprising a uniform distribution of the Mo 3 clusters compatible with local electroneutrality and chemical composition. The geometry of the triangular clusters with their oxygen environment (Mo 3 O 13 groups) has been directly visualized using differential phase contrast STEM imaging. The established local structure was used as input for density functional theory (DFT)-based calculations; they support the proposed atomic arrangement and provide a plausible explanation for the staircase galvanostatic charge profiles upon electrochemical Li + extraction from Li 2+x Mo 1−x O 3 in Li cells. According to DFT, all electrochemical capacity in Li 2+x Mo 1−x O 3 solely originates from the cationic Mo redox process, which proceeds via oxidation of the Mo 3 triangular clusters into bent Mo 3 chains where the electronic capacity of the clusters depends on the initial chemical composition and Mo oxidation state defining the width of the first charge low-voltage plateau. Further oxidation at the high-voltage plateau proceeds through decomposition of the Mo 3 chains into Mo 2 dimers and further into individual Mo 6+ cations.

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Section: ■ Introductionmentioning

confidence: 99%

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions

et al. 2022

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“…To fill these vacancies, electrons from higher energy levels transition to lower energy levels, emitting characteristic X-rays in the process as shown in Figure 4.3.3.1. These emitted X-rays uniquely represent the elements present in the sample and can be accurately plotted with high spatial resolution image from the TEM [384]. The EDS detects X-rays emitted from the whole illuminated sample volume that reach the detector.…”

Section: Spectroscopymentioning

confidence: 99%

Defect Engineering Of Perpendicular Magnetic Anisotropy In Cobalt-Based Thin Films

Mahendra

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Magnetic sensors have widespread applications in industrial, security, space, and biomedical fields, offering precise measurement of magnetic fields using principles like the Hall effect and magnetoresistance. Magnetic tunnel junctions (MTJs) have played a pivotal role in advancing magnetic sensing through tunnelling magnetoresistance (TMR), contributing to spintronic devices, memory systems, and magnetic sensors. The magnetic anisotropy of the reference ferromagnetic layer in MTJ sensors is a critical factor, influencing sensitivity, accuracy, and sensing direction. Perpendicular magnetic anisotropy (PMA) is particularly advantageous for detecting magnetic fields perpendicular to the sensor plane, opening possibilities in non-destructive testing and magnetic read heads. However, conventional sensors are restricted to fixed axes, hindering their ability to measure fields in three dimensions. To address this limitation, this thesis proposes a magnetic sensor with a tuneable sensing axis, enabling comprehensive field detection in all axes. As part of this exploration, the thesis investigates ion irradiation as a post-processing technique to modify the PMA of ferromagnetic layers, offering versatility for various applications.Cobalt-based materials, especially CoFeB, are well-known for their suitability in MTJs due to high TMR with MgO and PMA at low thicknesses. Half-metallic Heusler alloys, like Co2MnGa, have gained attention for their theoretically infinite TMR, high spin polarization, and high PMA. This research assesses the effects of ion irradiation on ultra-thin Co2MnGa and CoFeB stacks with PMA.Ion irradiation is a versatile tool for precisely tailoring magnetic stack properties with uniformity and reproducibility. This thesis investigates the impact of 30 keV Ar and Ne ion irradiation on CoFeB and Co2MnGa thin film stacks at low fluences (1 × 1013 to 1 × 1015 ion·cm−2), introducing displacement per atom (DPA) as a predictive parameter for ion-induced magnetic property changes. Results show a consistent reduction in PMA for both materials in half-MTJ stacks after irradiation, which is linked to intermixing of the magnetic layer with its adjacent MgO and heavy metal layers. Ar irradiation has a more pronounced effect due to higher DPA, while Ne irradiation has a milder impact. Co2MnGa displays relatively more resilience to irradiation due to reduced intermixing with adjacent layers, compared to CoFeB. Furthermore, the thesis explores the dynamic tuning of magnetic properties through ionic liquid gating, allowing anisotropy and coercivity manipulation via voltage control. It also delves into ion irradiation's potential to enhance the magneto-ionic effect. Lastly, a novel magnetic sensor design is introduced featuring a tuneable sensing axis, enabling three-dimensional detection capabilities.

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Electrode materials viewed with transmission electron microscopy

Cited by 2 publications

References 235 publications

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions

Defect Engineering Of Perpendicular Magnetic Anisotropy In Cobalt-Based Thin Films

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Electrode materials viewed with transmission electron microscopy

Cited by 2 publications

References 235 publications

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1–xO3 Solid Solutions

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li2+xMo1–xO3 Solid Solutions

Defect Engineering Of Perpendicular Magnetic Anisotropy In Cobalt-Based Thin Films

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Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions

Chemistry, Local Molybdenum Clustering, and Electrochemistry in the Li_2+xMo_1–xO₃ Solid Solutions