There is plenty of asbestos at the bottom. The case of magnesite raw material contaminated with asbestos fibres

Although all six asbestos minerals (the layer silicate chrysotile and five chain silicate species actinolite asbestos, amosite, anthophyllite asbestos, crocidolite and tremolite asbestos) are classified as carcinogenic, chrysotile is still mined and used in many countries worldwide. Other countries, like Italy, impose zero tolerance for all asbestos species, but conflicting views repress the development of globally uniform treaties controlling international trade of asbestos-containing materials. Hence, countries with more severe legislations against the use of these hazardous materials lack of an international safety net against importation of non-compliant products. This research reports the first discovery of commercial magnesite raw materials contaminated with white asbestos (chrysotile). X-ray powder diffraction and thermogravimetric/thermodifferential measurements showed the presence of serpentine group minerals in both the semi-processed (powder) and quarried material. The univocal identification of chrysotile in the powders was confirmed by its peculiar Raman bands of the OH stretching vibrations between 3500 and 3800 cm-1, with an intense peak at ∼3695 cm-1 and a weak contribution at ∼3647 cm-1. Transmission electron microscope showed that chrysotile forms fibres up to a few microns long and up to 80 nm thick with a nanotube structure characterized by inner channels as large as 30-40 nm. Fibres size analysis obtained by scanning electron microscopy indicates mean length and diameter of 5.95 and 0.109 μm with medians of 2.62 and 0.096 μm, respectively; some among the fibres analysed exhibit the so-called "Stanton size" (i.e., asbestos fibres longer than 8 μm and thinner than 0.25 μm that are strongly carcinogenic). Quantitative analysis showed a chrysotile content around 0.01 wt% not allowed by current regulations in Italy and many other countries. More generally, our findings demonstrate that without shared policies aimed at regulating asbestos circulation on the global market, "asbestos-free" national policies will inevitably fail.

Hexavalent chromium release over time from a pyrolyzed Cr-bearing tannery sludge

Pyrolysis in an inert atmosphere is a widely applied route to convert tannery wastes into reusable materials. In the present study, the Cr(III) conversion into the toxic hexavalent form in the pyrolyzed tannery waste referred to as KEU was investigated. Ageing experiments and leaching tests demonstrated that the Cr(III)-Cr(VI) inter-conversion occurs in the presence of air at ambient temperature, enhanced by wet environmental conditions. Microstructural analysis revealed that the Cr-primary mineral assemblage formed during pyrolysis (Cr-bearing srebrodolskite and Cr-magnetite spinel) destabilized upon spray water cooling in the last stage of the process. In the evolution from the higher to the lower temperature mineralogy, Cr is incorporated into newly formed CrOOH flakes which likely react in air forming extractable Cr(VI) species. This property transforms KEU from an inert waste to a hazardous material when exposed to ordinary ambient conditions.

The crystal structure of the killer fibre erionite from Tuzköy (Cappadocia, Turkey)

Erionite is a non-asbestos fibrous zeolite classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen and is considered today similar to or even more carcinogenic than the six regulated asbestos minerals. Exposure to fibrous erionite has been unequivocally linked to cases of malignant mesothelioma (MM) and this killer fibre is assumed to be directly responsible for more than 50% of all deaths in the population of the villages of Karain and Tuzköy in central Anatolia (Turkey). Erionite usually occurs in bundles of thin fibres and very rarely as single acicular or needle-like fibres. For this reason, a crystal structure of this fibre has not been attempted to date although an accurate characterization of its crystal structure is of paramount importance for our understanding of the toxicity and carcinogenicity. In this work, we report on a combined approach of microscopic (SEM, TEM, electron diffraction), spectroscopic (micro-Raman) and chemical techniques with synchrotron nano-single-crystal diffraction that allowed us to obtain the first reliable ab initio crystal structure of this killer zeolite. The refined structure showed regular T-O distances (in the range 1.61-1.65 Å) and extra-framework content in line with the chemical formula (K_2.63Ca₁.₅₇Mg_0.76Na_0.13Ba_0.01)[Si_28.62Al_7.35]O₇₂·28.3H₂O. The synchrotron nano-diffraction data combined with three-dimensional electron diffraction (3DED) allowed us to unequivocally rule out the presence of offretite. These results are of paramount importance for understanding the mechanisms by which erionite induces toxic damage and for confirming the physical similarities with asbestos fibres.

Copper nano-architecture topical cream for the accelerated recovery of burnt skin

Skin burns are debilitating injuries with significant morbidity and mortality associated with infections and sepsis, particularly in immunocompromised patients. In this context, nanotechnology can provide pioneering approaches for the topical treatment of burnt skin. Herein, the significant recovery of radiation-damaged skin by exploiting copper ultrasmall-in-nano architectures (CuNAs) dispersed in a home-made cosmetic cream is described and compared to other noble metals (such as gold). Owing to their peculiar design and components, CuNAs elicit a substantial recovery from burned skin in in vivo models after one topical application, and a significant anti-inflammatory effect is highlighted by reducing cytokine expression. The treatment exhibited neither significant toxicity nor the alteration of copper metabolism in the target organs because of the CuNA biocompatibility. This study may open new horizons in the treatment of radiation dermatitis and skin burns caused by other external events.

True molecular conformation and structure determination by three-dimensional electron diffraction of PAH by-products potentially useful for electronic applications

The true molecular conformation and the crystal structure of benzo[e]dinaphtho[2,3-a;1',2',3',4'-ghi]fluoranthene, 7,14-diphenylnaphtho[1,2,3,4-cde]bisanthene and 7,16-diphenylnaphtho[1,2,3,4-cde]helianthrene were determined ab initio by 3D electron diffraction. All three molecules are remarkable polycyclic aromatic hydrocarbons. The molecular conformation of two of these compounds could not be determined via classical spectroscopic methods due to the large size of the molecule and the occurrence of multiple and reciprocally connected aromatic rings. The molecular structure of the third molecule was previously considered provisional. These compounds were isolated as by-products in the synthesis of similar products and were at the same time nanocrystalline and available only in very limited amounts. 3D electron diffraction data, taken from submicrometric single crystals, allowed for direct ab initio structure solution and the unbiased determination of the internal molecular conformation. Detailed synthetic routes and spectroscopic analyses are also discussed. Based on many-body perturbation theory simulations, benzo[e]dinaphtho[2,3-a;1',2',3',4'-ghi]fluoranthene may be a promising candidate for triplet-triplet annihilation and 7,14-diphenylnaphtho[1,2,3,4-cde]bisanthene may be a promising candidate for intermolecular singlet fission in the solid state.

Halide perovskites as disposable epitaxial templates for the phase-selective synthesis of lead sulfochloride nanocrystals

Colloidal chemistry grants access to a wealth of materials through simple and mild reactions. However, even few elements can combine in a variety of stoichiometries and structures, potentially resulting in impurities or even wrong products. Similar issues have been long addressed in organic chemistry by using reaction-directing groups, that are added to a substrate to promote a specific product and are later removed. Inspired by such approach, we demonstrate the use of CsPbCl₃ perovskite nanocrystals to drive the phase-selective synthesis of two yet unexplored lead sulfochlorides: Pb₃S₂Cl₂ and Pb₄S₃Cl₂. When homogeneously nucleated in solution, lead sulfochlorides form Pb₃S₂Cl₂ nanocrystals. Conversely, the presence of CsPbCl₃ triggers the formation of Pb₄S₃Cl₂/CsPbCl₃ epitaxial heterostructures. The phase selectivity is guaranteed by the continuity of the cationic subnetwork across the interface, a condition not met in a hypothetical Pb₃S₂Cl₂/CsPbCl₃ heterostructure. The perovskite domain is then etched, delivering phase-pure Pb₄S₃Cl₂ nanocrystals that could not be synthesized directly.

Phase-selective approaches, such using reaction-directing groups, are often seen in traditional organic chemistry and catalysis. Here authors use perovskite nanocrystals as disposable templates to drive the phase-selective synthesis of two colloidal nanomaterials, the lead sulfohalides Pb₃S₂Cl₂ and Pb₄S₃Cl₂.

Structure determination, thermal stability and dissolution rate of δ-indomethacin

The structure solution of the δ-polymorph of indomethacin was obtained using three-dimensional electron diffraction. This form shows a significantly enhanced dissolution rate compared with the more common and better studied α- and γ-polymorphs, indicating better biopharmaceutical properties for medicinal applications. The structure was solved in non-centrosymmetric space group P2₁ and comprises two molecules in the asymmetric unit. Packing and molecule conformation closely resemble indomethacin methyl ester and indomethacin methanol solvate. Knowledge of the structure allowed the rational interpretation of spectroscopic IR and Raman data for δ-polymorph and a tentative interpretation for still unsolved indomethacin polymorphs. Finally, we observed a solid-solid transition from δ-polymorph to α-polymorph that can be driven by similarities in molecular conformation.

3D Electron Diffraction for Chemical Analysis: Instrumentation Developments and Innovative Applications

In the past few years, many exciting papers reported results based on crystal structure determination by electron diffraction. The aim of this review is to provide general and practical information to structural chemists interested in stepping into this emerging field. We discuss technical characteristics of electron microscopes for research units that would like to acquire their own instrumentation, as well as those practical aspects that appear different between X-ray and electron crystallography. We also include a discussion about applications where electron crystallography provides information that is different, and possibly complementary, with respect to what is available from X-ray crystallography.

The formation of impact coesite

Coesite in impact rocks is traditionally considered a retrograde product formed during pressure release by the crystallisation of an amorphous phase (either silica melt or diaplectic glass). Recently, the detailed microscopic and crystallographic study of impact ejecta from Kamil crater and the Australasian tektite strewn field pointed in turn to a different coesite formation pathway, through subsolidus quartz-to-coesite transformation. We report here further evidence documenting the formation of coesite directly from quartz. In Kamil ejecta we found sub-micrometric single-coesite-crystals that represent the first crystallization seeds of coesite. Coesite in Australasian samples show instead well-developed subeuhedral crystals, growing at the expenses of hosting quartz and postdating PDF deformation. Coesite (010) plane is most often parallel to quartz {10-11} plane family, supporting the formation of coesite through a topotactic transformation. Such reaction is facilitated by the presence of pre-existing and shock-induced discontinuities in the target. Shock wave reverberations can provide pressure and time conditions for coesite nucleation and growth. Because discontinuities occur in both porous and non-porous rocks and the coesite formation mechanism appears similar for small and large impacts, we infer that the proposed subsolidus transformation model is valid for all types of quartz-bearing target rocks.

3D Electron Diffraction Structure Determination of Terrylene, a Promising Candidate for Intermolecular Singlet Fission

Herein we demonstrate the prowess of the 3D electron diffraction approach by unveiling the structure of terrylene, the third member in the series of peri‐condensed naphthalene analogues, which has eluded structure determination for 65 years. The structure was determined by direct methods using electron diffraction data and corroborated by dispersion‐inclusive density functional theory optimizations. Terrylene crystalizes in the monoclinic space group P2₁/a, arranging in a sandwich‐herringbone packing motif, similar to analogous compounds. Having solved the crystal structure, we use many‐body perturbation theory to evaluate the excited‐state properties of terrylene in the solid‐state. We find that terrylene is a promising candidate for intermolecular singlet fission, comparable to tetracene and rubrene.

The structure of kaliophilite KAlSiO4, a long-lasting crystallographic problem

Kaliophilite is a feldspathoid mineral found in two Italian magmatic provinces and represents one of the 12 known phases with composition close to KAlSiO₄. Despite its apparently simple formula, the structure of this mineral revealed extremely complex and resisted structure solution for more than a century. Samples from the Vesuvius-Monte Somma and Alban Hills volcanic areas were analyzed through a multi-technique approach, and finally the crystal structure of kaliophilite was solved using 3D electron diffraction and refined against X-ray diffraction data of a twinned crystal. Results were also ascertained by the Rietveld method using synchrotron powder intensities. It was found that kaliophilite crystallizes in space group P3 with unit-cell parameters a = 27.0597 (16), c = 8.5587 (6) Å, V = 5427.3 (7) ų and Z = 54. The kaliophilite framework is a variant of the tridymite topology, with alternating SiO₄ and AlO₄ tetrahedra forming sheets of six-membered rings (6³ nets), which are connected along [001] by sharing the apical oxygen atoms. Considering the up (U) and down (D) orientations of the linking vertex, kaliophilite is the first framework that contains three different ring topologies: nine (1-3-5) (UDUDUD) rings, six (1-2-3) (UUUDDD) rings and twelve (1-2-4) (UUDUDD) rings. This results in a relatively open (19.9 tetrahedra nm^-3) channel system with multiple connections between the double six-ring cavities. Such a framework requires a surprisingly large unit cell, 27 times larger than the cell of kalsilite, the simplest phase with the same composition. The occurrence of some Na for K substitution (3-10%) may be related to the characteristic structural features of kaliophilite. Micro-twinning, pseudo-symmetries and anisotropic hkl-dependent peak broadening were also detected, and they may account for the elusive character of the kaliophilite crystal structure.

Electron Diffraction on Flash-Frozen Cowlesite Reveals the Structure of the First Two-Dimensional Natural Zeolite

Cowlesite, ideally Ca₆Al₁₂Si₁₈O₆₀·36H₂O, is to date the only natural zeolite whose structure could not be determined by X-ray methods. In this paper, we present the ab initio structure determination of this mineral obtained by three-dimensional (3D) electron diffraction data collected from single-crystal domains of a few hundreds of nanometers. The structure of cowlesite consists of an alternation of rigid zeolitic layers and low-density interlayers supported by water and cations. This makes cowlesite the only two-dimensional (2D) zeolite known in nature. When cowlesite gets in contact with a transmission electron microscope vacuum, a phase transition to a conventional 3D zeolite framework occurs in few seconds. The original cowlesite structure could be preserved only by adopting a cryo-plunging sample preparation protocol usually employed for macromolecular samples. Such a protocol allows the investigation by 3D electron diffraction of very hydrated and very beam-sensitive inorganic materials, which were previously considered intractable by transmission electron microscopy crystallographic methods.

Nanocrystals of Lead Chalcohalides: A Series of Kinetically Trapped Metastable Nanostructures

We report the colloidal synthesis of a series of surfactant-stabilized lead chalcohalide nanocrystals. Our work is mainly focused on Pb4S3Br2, a chalcohalide phase unknown to date that does not belong to the ambient-pressure PbS-PbBr2 phase diagram. The Pb4S3Br2 nanocrystals herein feature a remarkably narrow size distribution (with a size dispersion as low as 5%), a good size tunability (from 7 to ∼30 nm), an indirect bandgap, photoconductivity (responsivity = 4 ± 1 mA/W), and stability for months in air. A crystal structure is proposed for this new material by combining the information from 3D electron diffraction and electron tomography of a single nanocrystal, X-ray powder diffraction, and density functional theory calculations. Such a structure is closely related to that of the recently discovered high-pressure chalcohalide Pb4S3I2 phase, and indeed we were able to extend our synthesis scheme to Pb4S3I2 colloidal nanocrystals, whose structure matches the one that has been published for the bulk. Finally, we could also prepare nanocrystals of Pb3S2Cl2, which proved to be a structural analogue of the recently reported bulk Pb3Se2Br2 phase. It is remarkable that one high-pressure structure (for Pb4S3I2) and two metastable structures that had not yet been reported (for Pb4S3Br2 and Pb3S2Cl2) can be prepared on the nanoscale by wet-chemical approaches. This highlights the important role of colloidal chemistry in the discovery of new materials and motivates further exploration into metal chalcohalide nanocrystals.

Structural analysis of metastable pharmaceutical loratadine form II, by 3D electron diffraction and DFT+D energy minimisation

Coupling 3D electron diffraction and density functional theory provided the metastable pharmaceutical crystal structure within nanometre range, under ambient conditions.

Cs3Cu4In2Cl13 Nanocrystals: A Perovskite-Related Structure with Inorganic Clusters at A Sites

An effort to synthesize the Cu(I) variant of a lead-free double perovskite isostructural with Cs₂AgInCl₆ resulted in the formation of Cs₃Cu₄In₂Cl₁₃ nanocrystals with an unusual structure, as revealed by single-nanocrystal three-dimensional electron diffraction. These nanocrystals adopt a A₂BX₆ structure (K₂PtCl₆ type, termed vacancy ordered perovskite) with tetrahedrally coordinated Cu(I) ions. In the structure, 25% of the A sites are occupied by [Cu₄Cl]³⁺ clusters (75% by Cs⁺), and the B sites are occupied by In³⁺. Such a Cs₃Cu₄In₂Cl₁₃ compound prepared at the nanoscale is not known in the bulk and is an example of a multinary metal halide with inorganic cluster cations residing in A sites. The stability of the compound was supported by density functional theory calculations that also revealed that its bandgap is direct but parity forbidden. The existence of the Cs₃Cu₄In₂Cl₁₃ structure demonstrates that small inorganic cluster cations can occupy A sites in multinary metal halides.

We report the synthesis of Cs₃Cu₄In₂Cl₁₃ nanocrystals with a vacancy ordered A₂BX₆ perovskite structure, in which Cu(I) ions are tetrahedrally coordinated. In this new structure (determined by single-nanocrystal three-dimensional electron diffraction), 25% of the A sites are occupied by [Cu₄Cl]³⁺ clusters (75% by Cs⁺), while the B sites are occupied by In³⁺. Such a compound, not known in the bulk, is the first case of a perovskite-related structure with inorganic cluster cations residing in A sites.

Garnet, the archetypal cubic mineral, grows tetragonal

Garnet is the archetypal cubic mineral, occurring in a wide variety of rock types in Earth’s crust and upper mantle. Owing to its prevalence, durability and compositional diversity, garnet is used to investigate a broad range of geological processes. Although birefringence is a characteristic feature of rare Ca–Fe³⁺ garnet and Ca-rich hydrous garnet, the optical anisotropy that has occasionally been documented in common (that is, anhydrous Ca–Fe²⁺–Mg–Mn) garnet is generally attributed to internal strain of the cubic structure. Here we show that common garnet with a non-cubic (tetragonal) crystal structure is much more widespread than previously thought, occurring in low-temperature, high-pressure metamorphosed basalts (blueschists) from subduction zones and in low-grade metamorphosed mudstones (phyllites and schists) from orogenic belts. Indeed, a non-cubic symmetry appears to be typical of common garnet that forms at low temperatures (<450 °C), where it has a characteristic Fe–Ca-rich composition with very low Mg contents. We propose that, in most cases, garnet does not initially grow cubic. Our discovery indicates that the crystal chemistry and thermodynamic properties of garnet at low-temperature need to be re-assessed, with potential consequences for the application of garnet as an investigative tool in a broad range of geological environments.

3D Electron Diffraction: The Nanocrystallography Revolution

Crystallography of nanocrystalline materials has witnessed a true revolution in the past 10 years, thanks to the introduction of protocols for 3D acquisition and analysis of electron diffraction data. This method provides single-crystal data of structure solution and refinement quality, allowing the atomic structure determination of those materials that remained hitherto unknown because of their limited crystallinity. Several experimental protocols exist, which share the common idea of sampling a sequence of diffraction patterns while the crystal is tilted around a noncrystallographic axis, namely, the goniometer axis of the transmission electron microscope sample stage. This Outlook reviews most important 3D electron diffraction applications for different kinds of samples and problematics, related with both materials and life sciences. Structure refinement including dynamical scattering is also briefly discussed.

Structure analysis of materials at the order–disorder borderline using three-dimensional electron diffraction

Diffuse scattering, observed as intensity distribution between the Bragg peaks, is associated with deviations from the average crystal structure, generally referred to as disorder. In many cases crystal defects are seen as unwanted perturbations of the periodic structure and therefore they are often ignored. Yet, when it comes to the structure analysis of nano-volumes, what electron crystallography is designed for, the significance of defects increases. Twinning and polytypic sequences are other perturbations from ideal crystal structure that are also commonly observed in nanocrystals. Here we present an overview of defect types and review some of the most prominent studies published on the analysis of defective nanocrystalline structures by means of three-dimensional electron diffraction.

Daliranite, PbHgAs2S5: determination of the incommensurately modulated structure and revision of the chemical formula

The incommensurately modulated crystal structure of the mineral daliranite has been determined using 3D electron diffraction data obtained on nanocrystalline domains. Daliranite is orthorhombic with a = 21, b = 4.3, c = 9.5 Å and shows modulation satellites along c. The solution of the average structure in the Pnma space group together with energy-dispersive X-ray spectroscopy data obtained on the same domains indicate a chemical formula of PbHgAs2S5, which has one S fewer than previously reported. The crystal structure of daliranite is built from columns of face-sharing PbS8 bicapped trigonal prisms laterally connected by [2+4]Hg polyhedra and (As3+ 2S5)4− groups. The excellent quality of the electron diffraction data allows a structural model to be built for the modulated structure in superspace, which shows that the modulation is due to an alternated occupancy of a split As site.

The Crystal Structure of Orthocetamol Solved by 3D Electron Diffraction

Orthocetamol is a regioisomer of the well-known pain medication paracetamol and a promising analgesic and an anti-arthritic medicament itself. However, orthocetamol cannot be grown as single crystals suitable for X-ray diffraction, so its crystal structure has remained a mystery for more than a century. Here, we report the ab-initio structure determination of orthocetamol obtained by 3D electron diffraction, combining a low-dose acquisition method and a dedicated single-electron detector for recording the diffracted intensities. The structure is monoclinic, with a pseudo-tetragonal cell that favors multiple twinning on a scale of a few tens of nanometers. The successful application of 3D electron diffraction to orthocetamol introduces a new gold standard of total structure solution in all cases where X-ray diffraction and electron-microscope imaging methods fail.

Novel TEM Microscopy and Electron Diffraction Techniques to Characterize Cultural Heritage Materials: From Ancient Greek Artefacts to Maya Mural Paintings

To understand in-depth material properties, manufacturing, and conservation in cultural heritage artefacts, there is a strong need for advanced characterization tools that enable analysis down to the nanometric scale. Transmission electron microscopy (TEM) and electron diffraction (ED) techniques, like 3D precession electron diffraction tomography and ASTAR phase/orientation mapping, are proposed to study cultural heritage materials at nanoscale. In this work, we show how electron crystallography in TEM helps to determine precise structural information and phase/orientation distribution of various pigments in cultural heritage materials from various historical periods like Greek amphorisks, Roman glass tesserae, and pre-Hispanic Maya mural paintings. Such TEM-based methods can be an alternative to synchrotron techniques and can allow distinguishing accurately different crystalline phases even in cases of identical or very close chemical compositions at the nanometric scale.

Nanobeam precession-assisted 3D electron diffraction reveals a new polymorph of hen egg-white lysozyme

Recent advances in 3D electron diffraction have allowed the structure determination of several model proteins from submicrometric crystals, the unit-cell parameters and structures of which could be immediately validated by known models previously obtained by X-ray crystallography. Here, the first new protein structure determined by 3D electron diffraction data is presented: a previously unobserved polymorph of hen egg-white lysozyme. This form, with unit-cell parameters a = 31.9, b = 54.4, c = 71.8 Å, β = 98.8°, grows as needle-shaped submicrometric crystals simply by vapor diffusion starting from previously reported crystallization conditions. Remarkably, the data were collected using a low-dose stepwise experimental setup consisting of a precession-assisted nanobeam of ∼150 nm, which has never previously been applied for solving protein structures. The crystal structure was additionally validated using X-ray synchrotron-radiation sources by both powder diffraction and single-crystal micro-diffraction. 3D electron diffraction can be used for the structural characterization of submicrometric macromolecular crystals and is able to identify novel protein polymorphs that are hardly visible in conventional X-ray diffraction experiments. Additionally, the analysis, which was performed on both nanocrystals and microcrystals from the same crystallization drop, suggests that an integrated view from 3D electron diffraction and X-ray microfocus diffraction can be applied to obtain insights into the molecular dynamics during protein crystal growth.

A nanocrystalline monoclinic CaCO3 precursor of metastable aragonite

Despite its thermodynamical metastability at near-surface conditions, aragonite is widespread in marine and terrestrial sediments. It abundantly forms in living organisms, and its abiotic formation is favored in waters of a Mg²⁺/Ca²⁺ ratio > 1.5. Here, we provide crystallographic evidence of a nanocrystalline CaCO₃ polymorph, which precipitates before aragonite in a cave. The new phase, which we term monoclinic aragonite (mAra), is crystallographically related to ordinary, orthorhombic aragonite. Electron diffraction tomography combined with structure determination demonstrates that mAra has a layered aragonite structure, in which some carbonates can be replaced by hydroxyls and up to 10 atomic % of Mg can be incorporated. The diagnostic electron diffraction features of mAra are diffuse scattering and satellite reflections along aragonite {110}. Similar features have previously been reported-although unrecognized-from biogenic aragonite formed in stromatolites, mollusks, and cyanobacteria as well as from synthetic material. We propose that mAra is a widespread crystalline CaCO₃ that plays a hitherto unrecognized key role in metastable aragonite formation.

Ab Initio Structure Determination of Cu2- xTe Plasmonic Nanocrystals by Precession-Assisted Electron Diffraction Tomography and HAADF-STEM Imaging

We investigated pseudo-cubic Cu_{2- x}Te nanosheets using electron diffraction tomography and high-resolution HAADF-STEM imaging. The structure of this metastable nanomaterial, which has a strong localized surface plasmon resonance in the near-infrared region, was determined ab initio by 3D electron diffraction data recorded in low-dose nanobeam precession mode, using a new generation background-free single-electron detector. The presence of two different, crystallographically defined modulations creates a 3D connected vacancy channel system, which may account for the strong plasmonic response of this material. Moreover, a pervasive rotational twinning is observed for nanosheets as thin as 40 nm, resulting in a tetragonal pseudo-symmetry.

The structure of denisovite, a fibrous nanocrystalline polytypic disordered 'very complex' silicate, studied by a synergistic multi-disciplinary approach employing methods of electron crystallography and X-ray powder diffraction

Denisovite is a rare mineral occurring as aggregates of fibres typically 200-500 nm diameter. It was confirmed as a new mineral in 1984, but important facts about its chemical formula, lattice parameters, symmetry and structure have remained incompletely known since then. Recently obtained results from studies using microprobe analysis, X-ray powder diffraction (XRPD), electron crystallography, modelling and Rietveld refinement will be reported. The electron crystallography methods include transmission electron microscopy (TEM), selected-area electron diffraction (SAED), high-angle annular dark-field imaging (HAADF), high-resolution transmission electron microscopy (HRTEM), precession electron diffraction (PED) and electron diffraction tomography (EDT). A structural model of denisovite was developed from HAADF images and later completed on the basis of quasi-kinematic EDT data by ab initio structure solution using direct methods and least-squares refinement. The model was confirmed by Rietveld refinement. The lattice parameters are a = 31.024 (1), b = 19.554 (1) and c = 7.1441 (5) Å, β = 95.99 (3)°, V = 4310.1 (5) ų and space group P12/a1. The structure consists of three topologically distinct dreier silicate chains, viz. two xonotlite-like dreier double chains, [Si₆O₁₇]^10-, and a tubular loop-branched dreier triple chain, [Si₁₂O₃₀]^12-. The silicate chains occur between three walls of edge-sharing (Ca,Na) octahedra. The chains of silicate tetrahedra and the octahedra walls extend parallel to the z axis and form a layer parallel to (100). Water molecules and K⁺ cations are located at the centre of the tubular silicate chain. The latter also occupy positions close to the centres of eight-membered rings in the silicate chains. The silicate chains are geometrically constrained by neighbouring octahedra walls and present an ambiguity with respect to their z position along these walls, with displacements between neighbouring layers being either Δz = c/4 or -c/4. Such behaviour is typical for polytypic sequences and leads to disorder along [100]. In fact, the diffraction pattern does not show any sharp reflections with l odd, but continuous diffuse streaks parallel to a* instead. Only reflections with l even are sharp. The diffuse scattering is caused by (100) nano-lamellae separated by stacking faults and twin boundaries. The structure can be described according to the order-disorder (OD) theory as a stacking of layers parallel to (100).

(Na,□)5[MnO2]13 nanorods: a new tunnel structure for electrode materials determined ab initio and refined through a combination of electron and synchrotron diffraction data

(Na_x□_1 - x)₅[MnO₂]₁₃ has been synthesized with x = 0.80 (4), corresponding to Na_0.31[MnO₂]. This well known material is usually cited as Na_0.4[MnO₂] and is believed to have a romanèchite-like framework. Here, its true structure is determined, ab initio, by single-crystal electron diffraction tomography (EDT) and refined both by EDT data applying dynamical scattering theory and by the Rietveld method based on synchrotron powder diffraction data (χ² = 0.690, R_wp = 0.051, R_p = 0.037, R_F2 = 0.035). The unit cell is monoclinic C2/m, a = 22.5199 (6), b = 2.83987 (6), c = 14.8815 (4) Å, β = 105.0925 (16)°, V = 918.90 (4) ų, Z = 2. A hitherto unknown [MnO₂] framework is found, which is mainly based on edge- and corner-sharing octahedra and comprises three types of tunnels: per unit cell, two are defined by S-shaped 10-rings, four by egg-shaped 8-rings, and two by slightly oval 6-rings of Mn polyhedra. Na occupies all tunnels. The so-determined structure excellently explains previous reports on the electrochemistry of (Na,□)₅[MnO₂]₁₃. The trivalent Mn³⁺ ions concentrate at two of the seven Mn sites where larger Mn-O distances and Jahn-Teller distortion are observed. One of the Mn³⁺ sites is five-coordinated in a square pyramid which, on oxidation to Mn⁴⁺, may easily undergo topotactic transformation to an octahedron suggesting a possible pathway for the transition among different tunnel structures.

Ultrafast Electron Diffraction Tomography for Structure Determination of the New Zeolite ITQ-58

In this work a new ultrafast data collection strategy for electron diffraction tomography is presented that allows reducing data acquisition time by one order of magnitude. This methodology minimizes the radiation damage of beam-sensitive materials, such as microporous materials. This method, combined with the precession of the electron beam, provides high quality data enabling the determination of very complex structures. Most importantly, the implementation of this new electron diffraction methodology is easily affordable in any modern electron microscope. As a proof of concept, we have solved a new highly complex zeolitic structure named ITQ-58, with a very low symmetry (triclinic) and a large unit cell volume (1874.6 Å(3)), containing 16 silicon and 32 oxygen atoms in its asymmetric unit, which would be very difficult to solve with the state of the art techniques.

Hierachical Ni@Fe2O3 superparticles through epitaxial growth of γ-Fe2O3 nanorods on in situ formed Ni nanoplates

One endeavour of nanochemistry is the bottom-up synthesis of functional mesoscale structures from basic building blocks. We report a one-pot wet chemical synthesis of Ni@γ-Fe2O3 superparticles containing Ni cores densely covered with highly oriented γ-Fe2O3 (maghemite) nanorods (NRs) by controlled reduction/decomposition of nickel acetate (Ni(ac)2) and Fe(CO)5. Automated diffraction tomography (ADT) of the Ni-Fe2O3 interface in combination with Mössbauer spectroscopy showed that selective and oriented growth of the γ-Fe2O3 nanorods on the Ni core is facilitated through the formation of a Fe0.05Ni0.95 alloy and the appearance of superstructure features that may reduce strain at the Ni-Fe2O3 interface. The common orientation of the maghemite nanorods on the Ni core of the superparticles leads to a greatly enhanced magnetization. After functionalization with a catechol-functional polyethylene glycol (C-PEG) ligand the Ni@γ-Fe2O3 superparticles were dispersible in water.

Closing the gap between electron and X-ray crystallography

The development of a proper refinement algorithm that takes into account dynamical scattering guarantees, for electron crystallography, results approaching X-rays in terms of precision, accuracy and reliability. The combination of such dynamical refinement and electron diffraction tomography establishes a complete pathway for the structure characterization of single sub-micrometric crystals.