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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (31 January 2022) | Viewed by 26315

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Dr. Partha Pratim Das

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NanoMEGAS SPRL, Rue Èmile Claus 49 bte 9, 1050 Brussels, Belgium
Interests: electron crystallography; precession electron diffraction; nano-materials; organic pharmaceuticals; cultural heritage materials
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Dr. Arturo Ponce-Pedraza

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Department of Physics & Astronomy, The University of Texas at San Antonio, San Antonio, TX, USA
Interests: electron microscopy; metallic nanostructures; metal-oxides and ferroelectrics; crystallography of interfaces
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Dr. Enrico Mugnaioli

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Department of Earth Sciences, University of Pisa, Via S. Maria 53 - 56126 Pisa, Italy
Interests: electron crystallography; minerals; porous materials; nano-materials
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Dr. Stavros Nicolopoulos

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NanoMEGAS SPRL, Rue Èmile Claus 49 bte 9, 1050 Brussels, Belgium
Interests: precession electron diffraction; electron crystallography; phase and orinentation mapping, strain mapping; cultural heritage material
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Special Issue Information

Dear Colleagues,

Over the last decade, electron diffraction (ED) and structural imaging have received renewed interest from the scientific community due to the advances in TEM instrumentation (Cs correctors, direct detection cameras, 4D STEM) and the introduction of new techniques, such as beam precession, 3D electron diffraction and ptychography. Thus, the atomic structural characterisation of various types of materials (functional materials, energy materials, zeolites, minerals, organic compounds, pharmaceuticals and proteins) has become possible at the nm scale.

In particular, ED requires a far lower energy dose when compared to conventional imaging techniques, and therefore allows for the investigation of very beam-sensitive materials. ED is nowadays used for the atomic structure determination of new compounds (down to 50 nm in size), for the acquisition of phase, orientation and strain mapping, for the determination of electric fields and for the study of amorphous materials, which otherwise could not be studied by laboratory X-ray or synchrotron methods. Moreover, the development of in situ sample holders (gas, liquid, heating, etc.) has allowed for the study of (bio-) materials under close-to-natural conditions and of real-time reactions.

All these novel applications rely on or strongly benefit from the intrinsic symmetry of condensed matter at the atomic scale. Conventional crystals belong to one of the possible 230 space groups in 3D space, while the description of incommensurate materials requires a more complex formalism based on 4 to 6 dimensions. Even 2D or amorphous systems rely on specific assumptions of symmetry. Dynamic crystalline and symmetry evolution and phase transformations are characterised by external stimuli using in situ microscopy methods. This is the reason why we proposed this Special Issue of Symmetry entitled “Electron Diffraction and Structural Imaging”.

In this context, we welcome contributions covering any aspect of ED, structural imaging and other related in situ techniques that make use of consolidated or advanced TEM instrumentation and have potential applications for a wide range of materials.

Dr. Partha Pratim Das
Dr. Arturo Ponce-Pedraza
Dr. Enrico Mugnaioli
Dr. Stavros Nicolopoulos
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

nanomaterials
electron diffraction
4D STEM
serial ED
3D ED
microED
direct detection cameras
ptychography
in-situ
atomic imaging

Published Papers (11 papers)

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22 pages, 2802 KiB

Open AccessFeature PaperArticle

Structure Determination Feasibility of Three-Dimensional Electron Diffraction in Case of Limited Data

by Partha Pratim Das, Sergi Plana-Ruiz, Athanassios S. Galanis, Andrew Stewart, Fotini Karavasili, Stavros Nicolopoulos, Holger Putz, Irene Margiolaki, Maria Calamiotou and Gianluca Iezzi

Symmetry 2022, 14(11), 2355; https://doi.org/10.3390/sym14112355 - 08 Nov 2022

Viewed by 1815

Abstract

During the last two decades, three-dimensional electron diffraction (3D ED) has undergone a renaissance, starting with the introduction of precession (Precession Electron Diffraction Tomography, PEDT) that led to variations on the idea of collecting as much of the diffraction space as possible in order to solve crystal structures from sub-micron sized crystals. The most popular of these acquisition methods is based on the continuous tilting/rotation of the crystal (so-called Microcrystal Electron Diffraction, MicroED) akin to the oscillating crystal method in X-ray crystallography, which was enabled by the increase of sensitivity and acquisition speed in electron detectors. While 3D ED data is more complex than the equivalent X-ray data due to the higher proportion of dynamical scattering, the same basic principles of what is required in terms of data quality and quantity in order to solve a crystal structure apply; high completeness, high data resolution and good signal-to-noise statistics on measured reflection intensities. However, it may not always be possible to collect data in these optimum conditions, the most common limitations being the tilt range of the goniometer stage, often due to a small pole piece gap or the use of a non-tomography holder, or the position of the sample on the TEM grid, which may be too close to a grid bar and then the specimen of interest becomes occluded during tilting. Other factors that can limit the quality of the acquired data include the limited dynamic range of the detector, which can result on truncated intensities, or the sensitivity of the crystal to the electron beam, whereby the crystallinity of the particle is changing under the illumination of the beam. This limits the quality and quantity of the measured intensities and makes structure analysis of such data challenging. Under these circumstances, traditional approaches may fail to elucidate crystal structures, and global optimization methods may be used here as an alternative powerful tool. In this context, this work presents a systematic study on the application of a global optimization method to crystal structure determination from 3D ED data. The results are compared with known structure models and crystal phases obtained from traditional ab initio structure solution methods demonstrating how this strategy can be reliably applied to the analysis of partially complete 3D ED data. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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9 pages, 2266 KiB

Open AccessArticle

Ruddlesden–Popper Faults in NdNiO₃ Thin Films

by Chao Yang, Yi Wang, Daniel Putzky, Wilfried Sigle, Hongguang Wang, Roberto A. Ortiz, Gennady Logvenov, Eva Benckiser, Bernhard Keimer and Peter A. van Aken

Symmetry 2022, 14(3), 464; https://doi.org/10.3390/sym14030464 - 25 Feb 2022

Cited by 7 | Viewed by 2284

Abstract

The NdNiO₃ (NNO) system has attracted a considerable amount of attention owing to the discovery of superconductivity in Nd_0.8Sr_0.2NiO₂. In rare-earth nickelates, Ruddlesden–Popper (RP) faults play a significant role in functional properties, motivating our exploration of its microstructural characteristics and the electronic structure. Here, we employed aberration-corrected scanning transmission electron microscopy and spectroscopy to study a NdNiO₃ film grown by layer-by-layer molecular beam epitaxy (MBE). We found RP faults with multiple configurations in high-angle annular dark-field images. Elemental intermixing occurs at the SrTiO₃–NdNiO₃ interface and in the RP fault regions. Quantitative analysis of the variation in lattice constants indicates that large strains exist around the substrate–film interface. We demonstrate that the Ni valence change around RP faults is related to a strain and structure variation. This work provides insights into the microstructure and electronic-structure modifications around RP faults in nickelates. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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14 pages, 6543 KiB

Open AccessArticle

Characterization of Microstructure of Crept Nb and Ta-Rich γ-TiAl Alloys by Automated Crystal Orientation Mapping and Electron Back Scatter Diffraction

by Vajinder Singh, Chandan Mondal, Rajdeep Sarkar, Satabdi Roy, Chiptalluri Mohan Omprakash and Partha Ghosal

Symmetry 2022, 14(2), 399; https://doi.org/10.3390/sym14020399 - 17 Feb 2022

Viewed by 1300

Abstract

Understanding of the creep behavior Nb and Ta-rich γ-TiAl alloys plays a crucial role towards realization of their potential applications. The present article reports the evolution of microstructural features in the crept γ-TiAl-based Ti-5Al-8Nb-2Cr-0.2B and Ti-45Al-8Ta-0.2C-0.2B-0.2C alloys. Structural characterizations have been carried out using automated crystal orientation mapping (ACOM) along with precession electron diffraction (PED) in a transmission electron microscope, in conjunction with electron back-scattered diffraction (EBSD) in a scanning electron microscope (SEM) and transmission electron microscopy (TEM). Creep behavior of the fourth generation γ-TiAl-based alloys has been comparatively investigated under constant load tensile creep tests performed in the temperature range from 800–850 °C and applied stresses range of 125–200 MPa. It has been demonstrated that the ACOM with PED technique has accurate and reliable diffraction pattern recognition and higher spatial resolution, and supplements effectively the conventional EBSD technique for characterization of complex microstructural features evolved during creep of multiphase (γ + α₂ + β)-based TiAl alloys. The results show that the Nb and Ta additions have distinctly different effects on the microstructural instability and phase transformation during the creep deformation. The formation of the Ta-rich intermetallic phase (Ti₄Al₃Ta, the so-called τ phase) has been detected preferentially along the colony and the γ-α₂ interphase boundaries in the Ta-rich alloy, whilst its isomorph, Ti₄Al₃Nb intermetallic, has hardly been detected in the Nb-rich alloy. Implications of τ-phase formation and related microstructural instabilities have been discussed with respect to the creep behavior of the two alloys. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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18 pages, 29645 KiB

Open AccessArticle

Low-Dose Electron Crystallography: Structure Solution and Refinement

by Holger Klein, Stéphanie Kodjikian, Emre Yörük and Pierre Bordet

Symmetry 2022, 14(2), 245; https://doi.org/10.3390/sym14020245 - 26 Jan 2022

Cited by 3 | Viewed by 2117

Abstract

There is a wealth of materials that are beam sensitive and only exist in nanometric crystals, because the growth of bigger crystals is either impossible or so complicated that it is not reasonable to spend enough time and resources to grow big crystals before knowing their potential for research or applications. This difficulty is encountered in minerals, zeolites, metal-organic frameworks or molecular crystals, including pharmaceuticals and biological crystals. In order to study these crystals a structure determination method for beam sensitive crystals of nanometric size is needed. The nanometric size makes them destined for electron diffraction, since electrons interact much more strongly with matter than X-rays or neutrons. In addition, for the same amount of beam damage, electron diffraction yields more information than X-rays. The recently developed low-dose electron diffraction tomography (LD-EDT) not only combines the advantages inherent in electron diffraction, but is also optimized for minimizing the electron dose used for the data collection. The data quality is high, allowing not only the solution of complex unknown structures, but also their refinement taking into account the dynamical diffraction effects. Here we present several examples of crystals solved and refined by this method. The range of the crystals presented includes two synthetic oxides, Sr₅CuGe₉O₂₄ and (Na_2/3Mn_1/3)₃Ge₅O₁₂, a natural mineral (bulachite), and a metal organic framework (Mn-formiate). The dynamical refinement can be successfully performed on data sets that needed less than 0.1 e⁻/Å² for the entire data set. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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10 pages, 4471 KiB

Open AccessArticle

Identification of Retained Austenite in 9Cr-1.4W-0.06Ta-0.12C Reduced Activation Ferritic Martensitic Steel

by Rengachari Mythili, Ravi Kirana, Loushambam Herojit Singh, Ramanujam Govindaraj, Anil K. Sinha, Manvendra N. Singh, Saibaba Saroja, Muraleedharan Vijayalakshmi and Sudip K. Deb

Symmetry 2022, 14(2), 196; https://doi.org/10.3390/sym14020196 - 20 Jan 2022

Cited by 6 | Viewed by 1414

Abstract

Reduced activation ferritic martensitic (RAFM) 9Cr steels, which are candidate materials for the test blanket module (TBM) of nuclear fusion reactors, are considered to be air hardenable. However, alloy composition and the processing conditions play a significant role during the transformation of austenite to martensite/ferrite on cooling. The presence of retained austenite is known to influence the mechanical properties of the steel. Identifying very low amounts of retained austenite is very challenging though conventional microscopy. This paper aims at identifying a low amount of retained austenite in normalized 9Cr-1.4W-0.06Ta-0.12C RAFM steel using synchrotron X-ray diffraction and Mossbauer spectroscopy and confirmed by advanced automated crystal orientation mapping in transmission electron microscopy. Homogeneity of austenite has been understood to influence the microstructure of the normalized steel, which is discussed in detail. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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6 pages, 1208 KiB

Open AccessArticle

Electron Diffraction Study of the Space Group Variation in the Al–Mn–Pt T-Phase

by Rimon Tamari, Benjamin Grushko and Louisa Meshi

Symmetry 2022, 14(1), 38; https://doi.org/10.3390/sym14010038 - 29 Dec 2021

Cited by 1 | Viewed by 1177

Abstract

Binary high temperature “Al₃Mn” (T-phase) and its extensions in ternary systems were the subjects of numerous crystallographic investigations. The results were ambiguous regarding the existence or lack of the center of symmetry: both Pna2₁ and Pnam space groups were reported. Our research on the Al–Mn–Pt T-phase allowed concluding that inside a continuous homogeneity region, the structure of the Al-rich T-phase (e.g., Al₇₈Mn_17.5Pt_4.5) belongs to the non-centrosymmetric Pna2₁ space group, while the structure of the Al-poor T-phase (such as Al_71.3Mn_25.1Pt_3.6) is centrosymmetric, i.e., Pnam. Following metallurgical and crystallographic considerations, the change in the symmetry was explained. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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13 pages, 1801 KiB

Open AccessArticle

A Comparison of Structure Determination of Small Organic Molecules by 3D Electron Diffraction at Cryogenic and Room Temperature

by Taimin Yang, Steve Waitschat, Andrew Kentaro Inge, Norbert Stock, Xiaodong Zou and Hongyi Xu

Symmetry 2021, 13(11), 2131; https://doi.org/10.3390/sym13112131 - 09 Nov 2021

Cited by 8 | Viewed by 2709

Abstract

3D electron diffraction (3D ED), also known as micro-crystal electron diffraction (MicroED), is a rapid, accurate, and robust method for structure determination of submicron-sized crystals. 3D ED has mainly been applied in material science until 2013, when MicroED was developed for studying macromolecular crystals. MicroED was considered as a cryo-electron microscopy method, as MicroED data collection is usually carried out in cryogenic conditions. As a result, some researchers may consider that 3D ED/MicroED data collection on crystals of small organic molecules can only be performed in cryogenic conditions. In this work, we determined the structure for sucrose and azobenzene tetracarboxylic acid (H₄ABTC). The structure of H₄ABTC is the first crystal structure ever reported for this molecule. We compared data quality and structure accuracy among datasets collected under cryogenic conditions and room temperature. With the improvement in data quality by data merging, it is possible to reveal hydrogen atom positions in small organic molecule structures under both temperature conditions. The experimental results showed that, if the sample is stable in the vacuum environment of a transmission electron microscope (TEM), the data quality of datasets collected under room temperature is at least as good as data collected under cryogenic conditions according to various indicators (resolution, I/σ(I), CC_1/2 (%), R₁, R_int, ADRA). Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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17 pages, 31619 KiB

Open AccessArticle

Determination of Spinel Content in Cycled Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ Using Three-Dimensional Electron Diffraction and Precession Electron Diffraction

by Matthias Quintelier, Tyché Perkisas, Romy Poppe, Maria Batuk, Mylene Hendrickx and Joke Hadermann

Symmetry 2021, 13(11), 1989; https://doi.org/10.3390/sym13111989 - 20 Oct 2021

Cited by 1 | Viewed by 2263

Abstract

Among lithium battery cathode materials, Li_1.2Ni_0.13Mn_0.54Co_0.13O₂ (LR-NMC) has a high theoretical capacity, but suffers from voltage and capacity fade during cycling. This is partially ascribed to transition metal cation migration, which involves the local transformation of the honeycomb layered structure to spinel-like nano-domains. Determination of the honeycomb layered/spinel phase ratio from powder X-ray diffraction data is hindered by the nanoscale of the functional material and the domains, diverse types of twinning, stacking faults, and the possible presence of the rock salt phase. Determining the phase ratio from transmission electron microscopy imaging can only be done for thin regions near the surfaces of the crystals, and the intense beam that is needed for imaging induces the same transformation to spinel as cycling does. In this article, it is demonstrated that the low electron dose sufficient for electron diffraction allows the collection of data without inducing a phase transformation. Using calculated electron diffraction patterns, we demonstrate that it is possible to determine the volume ratio of the different phases in the particles using a pair-wise comparison of the intensities of the reflections. Using this method, the volume ratio of spinel structure to honeycomb layered structure is determined for a submicron sized crystal from experimental three-dimensional electron diffraction (3D ED) and precession electron diffraction (PED) data. Both twinning and the possible presence of the rock salt phase are taken into account. After 150 charge–discharge cycles, 4% of the volume in LR-NMC particles was transformed irreversibly from the honeycomb layered structure to the spinel structure. The proposed method would be applicable to other multi-phase materials as well. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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12 pages, 2728 KiB

Open AccessArticle

New Features in Crystal Orientation and Phase Mapping for Transmission Electron Microscopy

by Edgar F. Rauch, Patrick Harrison, Xuyang Zhou, Michael Herbig, Wolfgang Ludwig and Muriel Véron

Symmetry 2021, 13(9), 1675; https://doi.org/10.3390/sym13091675 - 11 Sep 2021

Cited by 13 | Viewed by 2522 | Correction

Abstract

ACOM/TEM is an automated electron diffraction pattern indexing tool that enables the structure, phase and crystallographic orientation of materials to be routinely determined. The software package, which is part of ACOM/TEM, has substantially evolved over the last fifteen years and has pioneered numerous additional functions with the constant objective of improving its capabilities to make the tremendous amount of information contained in the diffraction patterns easily available to the user. Initially devoted to the analysis of local crystallographic texture, and as an alternative to both X-ray pole figure measurement and EBSD accessories for scanning electron microscopes, it has rapidly proven itself effective to distinguish multiple different phases contained within a given sample, including amorphous phases. Different strategies were developed to bypass the inherent limitations of transmission electron diffraction patterns, such as 180° ambiguities or the complexity of patterns produced from overlapping grains. Post processing algorithms have also been developed to improve the angular resolution and to increase the computing rate. The present paper aims to review some of these facilities. On-going works on 3D reconstruction are also introduced. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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15 pages, 16391 KiB

Open AccessArticle

Comprehensive Study of Li⁺/Ni²⁺ Disorder in Ni-Rich NMCs Cathodes for Li-Ion Batteries

by Elena D. Orlova, Aleksandra A. Savina, Sergey A. Abakumov, Anatolii V. Morozov and Artem M. Abakumov

Symmetry 2021, 13(9), 1628; https://doi.org/10.3390/sym13091628 - 03 Sep 2021

Cited by 28 | Viewed by 3864

Abstract

The layered oxides LiNi_xMn_yCo_zO₂ (NMCs, x + y + z = 1) with high nickel content (x ≥ 0.6, Ni-rich NMCs) are promising high-energy density-positive electrode materials for Li-ion batteries. Their electrochemical properties depend on Li⁺/Ni²⁺ cation disordering originating from the proximity of the Li⁺ and Ni²⁺ ionic radii. We synthesized a series of the LiNi₀.₈Mn₀.₁Co₀.₁O₂ NMC811 adopting two different disordering schemes: Ni for Li substitution at the Li site in the samples finally annealed in air, and close to Ni↔Li antisite disorder in the oxygen-annealed samples. The defect formation scenario was revealed with Rietveld refinement from powder X-ray diffraction data, and then the reliability of semi-quantitative parameters, such as I₀₀₃/I₁₀₄ integral intensity ratio and c/(2√6a) ratio of pseudocubic subcell parameters, was verified against the refined defect concentrations. The I₀₀₃/I₁₀₄ ratio can serve as a quantitative measure of g(Ni_Li) only after explicit correction of intensities for preferred orientation. Being normalized by the total scattering power of the unit cell, the I₀₀₃/I₁₀₄ ratio depends linearly on g(Ni_Li) for each disordering scheme. The c/(2√6a) ratio appears to be not reliable and cannot be used for a quantitative estimate of g(Ni_Li). In turn, the volume of the R

\bar{3}

m unit cell correlates linearly with g(Ni_Li), at least for defect concentrations not exceeding 5%. The microscopy techniques such as high-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and electron diffraction tomography (EDT) allow us to study the materials locally, still, there is no proper quantitative approach for comprehensive analysis of defects. In the present work, the TEM-assisted quantitative Li⁺/Ni²⁺ disordering analysis with EDT and HAADF-STEM in six Ni-rich NMC samples with various defects content is demonstrated. Noteworthy, while PXRD and EDT methods demonstrate overall defect amounts, HAADF-STEM allows us to quantitatively distinguish regions with various disordering extents. Therefore, the combination of mentioned PXRD and TEM methods gives the full picture of Li⁺/Ni²⁺ mixing defects in Ni-rich NMCs. Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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1 pages, 188 KiB

Open AccessCorrection

Correction: Rauch et al. New Features in Crystal Orientation and Phase Mapping for Transmission Electron Microscopy. Symmetry 2021, 13, 1675

by Edgar F. Rauch, Patrick Harrison, Xuyang Zhou, Michael Herbig, Wolfgang Ludwig and Muriel Véron

Symmetry 2021, 13(12), 2339; https://doi.org/10.3390/sym13122339 - 06 Dec 2021

Cited by 1 | Viewed by 1432

Abstract

The authors wish to make the following corrections to this paper [...] Full article

(This article belongs to the Special Issue Electron Diffraction and Structural Imaging)

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