Single-crystal Electron Diffraction Research Articles

A Porous Cobalt Tetraphosphonate Metal-Organic Framework: Accurate Structure and Guest Molecule Location Determined by Continuous-Rotation Electron Diffraction.

Single-crystal electron diffraction has shown to be powerful for structure determination of nano- and submicron-sized crystals that are too small to be studied by single-crystal X-ray diffraction. However, it has been very challenging to obtain high quality electron diffraction data from beam sensitive crystals such as metal-organic frameworks (MOFs). It is even more difficult to locate guest species in the pores of MOF crystals. Here, we present synthesis of a novel porous cobalt MOF with 1D channels, [Co2 (Ni-H4 TPPP)]⋅2 DABCO⋅6 H2 O, (denoted Co-CAU-36; DABCO=1,4-diazabicyclo[2.2.2]octane), and its structure determination using continuous rotation electron diffraction (cRED) data. By combining a fast hybrid electron detector with low sample temperature (96 K), high resolution (0.83-1.00 Å) cRED data could be obtained from eight Co-CAU-36 crystals. Independent structure determinations were conducted using each of the eight cRED datasets. We show that all atoms in the MOF framework could be located. More importantly, we demonstrate for the first time that organic molecules in the pores, which were previously difficult to find, could be located using the cRED data. A comparison of eight independent structure determinations using different datasets shows that structural models differ only on average by 0.03(2) Å for the framework atoms and 0.10(6) and 0.16(12) Å for DABCO and water molecules, respectively.

Crystal structure analysis of a star-shaped triazine compound: a combination of single-crystal three-dimensional electron diffraction and powder X-ray diffraction

The solid-state structure of star-shaped 2,4,6-tris{(E)-2-[4-(dimethylamino)-phenyl]ethenyl}-1,3,5-triazine is determined from a powder sample by exploiting the respective strengths of single-crystal three-dimensional electron diffraction and powder X-ray diffraction data. The unit-cell parameters were determined from single crystal electron diffraction data. Using this information, the powder X-ray diffraction data were indexed, and the crystal structure was determined from the powder diffraction profile. The compound crystallizes in a noncentrosymmetric space group, P212121. The molecular conformation in the crystal structure was used to calculate the molecular dipole moment of 3.22 Debye, which enables the material to show nonlinear optical effects.

Morphology and stability of orthorhombic and hexagonal phases in a lamellar γ-Ti-42Al-8.5Nb alloy-A transmission electron microscopy study

Intermetallic titanium aluminides are often alloyed with niobium to improve oxidation resistance and mechanical properties. Depending on the overall alloy composition and on the solubility of the present phases for niobium, new phases may be introduced in the alloys' microstructure upon niobium addition. Here we describe the microstructure of the alloy Ti-42Al-8.5Nb produced by powder metallurgy after annealing at 550 °C and 650 °C. We identify the orthorhombic O-phase within α2 laths of lamellar (α2 + γ) colonies by single crystal electron diffraction and high-resolution imaging. Domains of O-phase variants and α2 phase form columnar crystallites in α2 (0001) planes having low indexed α2 {11-20} and {1-100} interface planes. The nm-sized domains are rotated with respect to each other resulting in elastic strains across the domain boundaries. No elemental segregation of Nb was detected in α2/O-phase lamellae.

(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.

(Nax□1 - x)5[MnO2]13 has been synthesized with x = 0.80 (4), corresponding to Na0.31[MnO2]. This well known material is usually cited as Na0.4[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, Rwp = 0.051, Rp = 0.037, RF2 = 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) Å3, 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.

Characterization and activity of V2O5-CeO2/TiO2-ZrO2 catalysts for NH3-selective catalytic reduction of NOx

A series of V2O5-xCeO2/TiO2-ZrO2 (Ti-Zr) catalysts with different CeO2 loadings (x = molar ratio of Ce/Ti-Zr) were prepared, and their catalytic performance for the selective catalytic reduction (SCR) of NOx by NH3 was investigated in the presence of SO2 and H2O. The physicochemical properties of the catalysts were characterized by N2 sorption analysis, high-resolution transmission electron microscopy, X-ray diffraction, H2-temperature-programmed reduction, NH3-temperature-programmed desorption, and in situ diffuse reflectance infrared Fourier transform spectroscopy. The presence of CeO2 in the catalysts led to higher conversion of NOx within a wider operating temperature range. V2O5-xCeO2/Ti-Zr catalyst (x = 0.2) exhibited the highest activity. Higher loadings of CeO2 adversely affected the NOx conversion at higher temperatures. The characterization results revealed that CeO2 was amorphous and highly dispersed over the Ti-Zr support. The catalysts featured single-crystal electron diffraction features. The presence of CeO2 significantly increased the reduction ability of the catalysts, and low V2O5 loadings were beneficial to the low-temperature SCR. V2O5/TiO2 catalyst exhibited medium-to-strong and strong acid desorption of NH3, whereas V2O5/Ti-Zr featured weak acid sites onto which desorption of NH3 occurred. The presence of CeO2 could increase the amount of both the Brönsted and Lewis acid sites, which were expected to play a key role in the excellent SCR activity. In contrast, the presence of V2O5 reduced the amount of Brönsted acid sites. All V2O5-CeO2/Ti-Zr catalysts exhibited poor stability and weak resistance to H2O poisoning but high resistance to SO2. However, the original catalytic activity of V2O5-xCeO2/Ti-Zr (x = 0.3) could be fully restored following poisoning with SO2 and H2O. For the poisoned catalysts, the formation of Ce(SO4)2 led to the decreased catalytic performance at the intermediate temperatures, which increased at the higher temperatures because of the presence of V2O5.

Preferential Incorporation of Azelaic Acid Units into the Crystalline Phase of the Copoly(Alkylene Dicarboxylate) Derived from 1,9-Nonanediol and an Equimolar Mixture of Pimelic and Azelaic Acids

The crystalline structure of two biodegradable odd-odd polyesters (i.e., poly(nonamethylene pimelate) (PES 9,7) and poly(nonamethylene azelate) (PES 9,9)) was investigated by means of electron and X-ray diffraction of single crystals and oriented fibers, respectively. Truncated rhombic crystals were obtained with an aspect ratio that was strongly depended on the supercooling degree. The crystalline structure of both homopolyesters was defined by an orthorhombic P21ab space group and a large unit cell containing four molecular segments with an all-trans conformation. Nevertheless, the structure in the chain axis projection was equivalent to a simpler cell containing only two segments. Crystalline lamellae were effectively degraded by lipases, starting the enzymatic attack on the lamellar surfaces. The random copolymer constituted by an equimolar amount of pimelate and azelate units (COPES 9,7/9) crystallized according to regular lamellae with a similar molecular arrangement in the chain axis projection. The structure of this copolymer was preferably conditioned by the azelate component as could be deduced from both, diffraction and spectroscopic data. Analysis of small angle X-ray scattering patterns pointed out that less crystalline lamellae with higher amorphous thickness had developed in the copolymer. This feature was interpreted as a consequence of the preferential incorporation of pimelate comonomer units in the folding surface.

Series of Highly Stable Isoreticular Lanthanide Metal–Organic Frameworks with Expanding Pore Size and Tunable Luminescent Properties

A series of highly porous isoreticular lanthanide-based metal–organic frameworks (LnMOFs) denoted as SUMOF-7I to SUMOF-7IV (SU = Stockholm University; Ln = La, Ce, Pr, Nd, Sm, Eu, and Gd) have been synthesized using tritopic carboxylates as the organic linkers. The SUMOF-7 materials display one-dimensional pseudohexagonal channels with the pore diameter gradually enlarged from 8.4 to 23.9 Å, as a result of increasing sizes of the organic linkers. The structures have been solved by single crystal X-ray diffraction or rotation electron diffraction (RED) combined with powder X-ray diffraction (PXRD). The SUMOF-7 materials exhibit robust architectures with permanent porosity. More importantly, they exhibit exceptionally high thermal and chemical stability. We show that, by inclusion of organic dye molecules, the luminescence properties of the MOFs can be elaborated and modulated, leading to promising applications in sensing and optics.

Classical and nonclassical germanium environments in high-pressure BaGe5.

A new crystalline form of BaGe(5) was obtained at a pressure of 15(2) GPa in the temperature range from 1000(100) to 1200(120) K. Single-crystal electron and powder X-ray diffraction patterns indicate a body-centered orthorhombic structure (space group Imma, Pearson notation oI24) with unit cell parameters a = 8.3421(8) Å, b = 4.8728(5) Å, and c = 13.7202(9) Å. The crystal structure of hp-BaGe(5) consists of four-bonded Ge atoms forming complex layers with Ge-Ge contacts between 2.560(6) and 2.684(3) Å; the Ba atoms are coordinated by 15 Ge neighbors in the range from 3.341(6) to 3.739(4) Å. Analysis of the chemical bonding using quantum chemical techniques in real space reveal charge transfer from the Ba cations to the anionic Ge species. Ge atoms having nearly tetrahedral environments show an electron-localizability-based oxidation number close to 0; the four-bonded Ge atoms with a Ψ-pyramidal environment adopt a value close to 1-. In agreement with the calculated electronic density of states, the compound is a metallic conductor (electrical resistivity of ca. 240 μΩ cm at 300 K), and magnetic susceptibility measurements evidence diamagnetic behavior with χ(0) = -95 × 10(-6) emu mol(-1).

Single Crystal 3D Rotation Electron Diffraction from Nano-sized Crystals

Electron crystallography is an important technique for structure analysis of nano-sized materials. Crystals too small or too complicated to be studied by X-ray diffraction can be investigated by electron crystallography. However, conventional TEM methods requires high TEM skills and strong crystallographic knowledge, which many synthetic materials scientists and chemists do not have. We recently developed the software-based Rotation Electron Diffraction (RED) method for automated collection and processing of 3D electron diffraction data. Complete single crystal 3D electron diffraction data can be collected from nano- and micron-sized crystals in less than one hour by combining electron beam tilt and goniometer tilt, which are controlled by the RED – data collection software.3 The unit cell, possible space groups and electron diffraction intensities can be obtained from the RED data using the RED data processing software. The figure below illustrates the data collection and data processing of a zeolite silicalite-1 by RED. 1427 ED frames were collected in less than 1 hour from a crystal of 800 x 400 x 200 nm in size. A 3D reciprocal lattice of silicalite-1 was reconstructed from the ED frames, from which the unit cell parameters and space group were determined (P21/n, a=20.02Å, b=20.25Å, c=13.35Å, alfa=90.130, beta=90.740, gamma=90.030. It was possible to cut the 3D reciprocal lattice perpendicular to any directions and study the reflection conditions. The reflection intensities could be extracted. The structure of the calcined silicalite-1 could be solved from the RED data by routine direct methods using SHELX-97. All 78 unique Si and O atoms could be located and refined to an accuracy better than 0.08 Å. The RED method has been applied for structure solution of a wide range of crystals and shown to be very powerful and efficient. Now a structure determination can be achieved within a few hours, from the data collection to structure solution. We will present several examples including unknown inorganic compounds, metal-organic frameworks and organic structures solved from the RED data. Different parameters that affect the RED data quality and thus the structure determination will be discussed. The methods are general and can be applied to any crystalline materials.

Quasicrystal approximants solved by Rotation Electron Diffraction (RED)

We have developed single crystal electron diffraction for powder-sized samples, i.e. < 0.1μm in all dimensions. Complete 3D electron diffraction is collected by Rotation Electron Diffraction (RED) in about one hour. Data processing takes another hour. The crystal structures are solved by standard crystallographic techniques. X-ray crystallography requires crystals several micrometers big. For nanometer sized crystals, electron diffraction and electron microscopy (EM) are the only possibilities. Modern transmission EMs are equipped with the two things that are necessary for turning them into automatic single crystal diffractometers; they have CCD cameras and all lenses and the sample stage are computer-controlled. Two methods have been developed for collecting complete (except for a missing cone) 3D electron diffraction data; the Rotation Electron Diffraction (RED) [1] and Automated Electron Diffraction Tomography (ADT) by Kolb et al. [2]. Because of the very strong interaction between electrons and matter, an electron diffraction pattern with visible spots is obtained in one second from a submicron sized crystal in the EM. By collecting 1000-2000 electron diffraction patterns, a complete 3D data set is obtained. The geometry in RED is analogous to the rotation method in X-ray crystallography; the sample is rotated continuously along one rotation axis. The data processing results in a list of typically over 1000 reflections with h,k,l and Intensity. The unit cell is typically obtained correctly to within 1%. Space group determination is done as in X-ray crystallography from systematically absent reflections, but special care must be taken because occasionally multiple electron diffraction can give rise to very strong forbidden reflections. At +/-60° tilt with 0.1° steps, a complete data collection will be some 1200 frames. With one second exposures this takes about one hour. There is no need to align the crystal orientation. The reciprocal lattice can be rotated and displayed at any direction of view. Sections such as hk0, hk1, hk2, h0l and so on can easily be cut out and displayed. We have solved over 50 crystal structures by RED in one year. These include the most complex zeolites ever solved and quasicrystal approximants, such as the pseudo-decagonal approximants PD2 [3] and PD1 in AlCoNi. Observed and calculated sections of reciprocal space (cut at 1.0Å) are shown in Fig. 1. Notice the 10-fold symmetry of strong reflections.

Why powder diffractionists need help from electron crystallography

Although X-ray powder diffraction (XPD) is used as a routine tool for solving crystal structures of polycrystalline materials, its weakness is obvious: not only is the phase information lost during the diffraction experiment, but reflections with similar d-spacings, which are well-separated in a single-crystal measurement, overlap in a powder pattern. These effects increase the difficulty of structure solution especially when dealing with complex structures. Compared to XPD, the advantages from electron microscopy are: (1) single-crystal electron diffraction data, either in 2-dimensional or 3-dimensional form, can be obtained from a very tiny crystallite in a powder sample; and (2) high-resolution images can be collected and used to extract phase information in reciprocal space or to provide a direct view of structural features (ordered and disordered) [1]. With the extra information supplied by electron microscopy, the limits of structure determination for polycrystalline materials can be extended [2]. Here we will present a few examples to demonstrate why powder diffractionists need help from electron microscopy and how to integrate these two techniques into the structure determination process.

Research on the Size Distribution of Intragranular and Boundary Carbides of T91 Steel after Creep

The high temperature crept tests of T91 steel have been conducted under two different stresses and temperatures. The single crystal electron diffraction is used to identify the precipitated phase structure. The quantity and size of carbides located in boundaries and intragranular area have been obtained by quantitative metallography, respectively. The results showed that the main precipitated carbides in T91 steel are M23C6(M=Fe,Cr) and V4C3,which is located in the grain and at the boundary of prior austenite respectively. In comparison with the carbides at boundary, the average size of intragranular carbides was smaller while the quantity is higher. The distribution of the carbides size crept with different stresses and temperatures is in accordance with a typical Boltzmann distribution.

Ab initio structure determination of interlayer expanded zeolites by single crystal rotation electron diffraction.

Layered solids often form thin plate-like crystals that are too small to be studied by single-crystal X-ray diffraction. Although powder X-ray diffraction (PXRD) is the conventional method for studying such solids, it has limitations because of peak broadening and peak overlapping. We have recently developed a software-based rotation electron diffraction (RED) method for automated collection and processing of 3D electron diffraction data. Here we demonstrate the ab initio structure determination of two interlayer expanded zeolites, the microporous silicates COE-3 and COE-4 (COE-n stands for International Network of Centers of Excellence-n), from submicron-sized crystals by the RED method. COE-3 and COE-4 are built of ferrierite-type layers pillared by (-O-Si(CH3)2-O-) and (-O-Si(OH)2-O-) linker groups, respectively. The structures contain 2D intersecting 10-ring channels running parallel to the ferrierite layers. Because both COE-3 and COE-4 are electron-beam sensitive, a combination of RED datasets from 2 to 3 different crystals was needed for the structure solution and subsequent structure refinement. The structures were further refined by Rietveld refinement against the PXRD data. The structure models obtained from RED and PXRD were compared.

Origins of Phase Transitions in Valence Fluctuating YbPd

The cubic YbPd compound undergoes two first-order phase transitions at \(T_{1}=125\) K and \(T_{2}=105\) K. We report the experimental results of the X-ray diffraction (XRD) and electron diffraction of single crystals of YbPd at low temperatures. Below \(T_{1}\), the \((h00)\) Bragg peaks (\(h\): an integer) are split into two subpeaks. Below \(T_{2}\), the superlattice reflections of \((n/2,0,0)\) (\(n\): an odd number) in the XRD patterns and the superlattice spots of \((1/2,0,0)\), \((0,1/2,0)\), and \((1/2,1/2,0)\) in the electron diffraction profile appear, which suggests the valence order of YbPd. We discuss two possible structures, assuming a tetragonal symmetry below \(T_{1}\). The origins of the transitions at \(T_{1}\) and \(T_{2}\) are probably the band Jahn–Teller effect and the valence order, respectively.

Reverse Monte Carlo refinements of nanoscale atomic correlations using powder and single-crystal diffraction data

Combined refinements of local atomic structure that involve simultaneous fitting of powder-averaged and single-crystal data were implemented as an extension to the publicly availableRMCProfilesoftware. The refinements employ the reverse Monte Carlo method to fit neutron total scattering data, the neutron Bragg profile, extended X-ray absorption fine structure (EXAFS) and structured diffuse scattering in electron diffraction. The procedure was tested using simulated data generated for a realistic model of perovskite-like KNbO3, which exhibits strongly correlated Nb and O displacements. The results indicated that fitting the powder data (i.e.total scattering or total scattering plus EXAFS) alone fails to reproduce the nanoscale range of displacement correlations. Simultaneous fitting of the powder data and the patterns of diffuse intensity in single-crystal electron diffraction patterns returns significantly more accurate correlation characteristics. The approach and the computer software described in this contribution are not limited to electron diffraction patterns as other types of single-crystal diffraction data (i.e.X-ray or neutron) can be included in the fit.

Variability in sepiolite: Diffraction studies

Twenty sepiolites of known composition from different origins were analyzed to quantify the variability in structural parameters and its possible relationships with composition and morphology. Morphology SEM analyses led to classify the sepiolites into several groups, beyond the two simple macroscopic or clay groups. X-ray powder diffraction with synchrotron light was used to discuss the variability of the a and b cell parameters with the nature of the cations and occupancy of the octahedral shell. Rietveld refinement using the ideal sepiolite model is performed on sepiolites at two temperatures: 225 °C (for zeolitically dehydrated sepiolite) and 25 °C (for hydrated ambient sepiolite). The latter permitted to locate ca. six molecules of the zeolitic H2O within the tunnels. A few samples were selected to evaluate the feasibility and potential of single-crystal diffraction methods: X-ray microdiffraction and electron diffraction. The macroscopic sepiolites gave well-structured and rich X-ray fiber diffraction patterns, in excellent agreement with ab initio simulations. High-quality single-crystal electron diffraction patterns for three axis zones are indexed and compared with simulations. The experimental and modeling results for X-ray microdiffraction and electron diffraction open a new path for quantitative crystallography on sepiolite and other fibrous clays from the sepiolite-palygorskite group.

Introduction to electron crystallography

AbstractEverything in Nature, macroscopic or microscopic, inorganic, organic or biological, has its specific properties. Most properties of matter depend on the atomic structures, and many techniques have been developed over the centuries for structure analysis. The greatest of them all, structure analysis of single crystals by X‐ray diffraction, X‐ray crystallography, was founded in 1912, and remains the most important technique for studying structures of periodically ordered objects at atomic resolution. Electron diffraction of single crystals was discovered fifteen years later by Thomson, Davisson and Germer. The wave property of electrons was exploited in the invention of the electron microscope by Knoll and Ruska in 1932. Since then, electron microscopes have been used in many fields as a tool for exploring and visualising the microscopic world in all its beauty. Between the first blurred images and today's sharp atomic resolution lies seventy years of untiring engineering. More recently, the unprecedented power of computers has made it possible to analyse quantitatively, and even further improve, these images. The amalgamation of electron diffraction and atomic resolution electron microscopy with crystallographic image processing has created a new powerful tool for structure analysis ‐ electron crystallography. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Microstructure and magnetic behavior of compounds in the solid solution system Li [Ni 1 − xMn x] O 2 ( x = 0.3, 0.5, 0.7)

Layered transition metal oxides containing more than one transition element are considered for applications in electric vehicles. In these compounds new and improved properties may result from the combination of element specific properties. At the same time the arrangement of species within the transition metal layer is one aspect that may affect the Li intercalation behavior and hence the electrochemical properties. Here we present a microstructural study on a series of Li [Ni 1 − x Mn x ] O 2 compounds where the oxidations state and arrangement of TM ions are characterized by SQUID magnetometry and single crystal electron diffraction. Our results show that in-plane long range ordering increases with Mn content and that Li/Ni interchange takes place in all powders but seems to be highest in Mn-rich compositions. During chemical delithiation Li is removed from the TM layers leading to a decrease in percentage of long range ordering.

Electron diffraction, X-ray powder diffraction and pair-distribution-function analyses to determine the crystal structures of Pigment Yellow 213, C23H21N5O9

The crystal structure of the nanocrystalline alpha phase of Pigment Yellow 213 (P.Y. 213) was solved by a combination of single-crystal electron diffraction and X-ray powder diffraction, despite the poor crystallinity of the material. The molecules form an efficient dense packing, which explains the observed insolubility and weather fastness of the pigment. The pair-distribution function (PDF) of the alpha phase is consistent with the determined crystal structure. The beta phase of P.Y. 213 shows even lower crystal quality, so extracting any structural information directly from the diffraction data is not possible. PDF analysis indicates the beta phase to have a columnar structure with a similar local structure as the alpha phase and a domain size in column direction of approximately 4 nm.

Nanoscale single-crystal vanadium oxides with layered structure by electrospinning and hydrothermal methods

The application of electrospinning technique in hydrothermally producing single-crystal vanadium oxide nanorods is described. Vanadium oxide nanorods with a width of less than 100 nm have been formed at the sites of the electrospun composite fibers which themselves lack a crystalline structure. Lithium cations can be incorporated into the compounds by changing the aqueous solution during the hydrothermal process. X-ray powder diffraction indicates that both nanorods have a lamellar structure, with the interlayer distance in lithium vanadium oxide being shorter than in the vanadium oxide. Each nanorod exhibits single-crystal electron diffraction pattern. The morphology is controlled by the electrospinning process as shown by TEM and SEM studies. The vanadium oxidation state in the lithium vanadium oxide nanorods is + 4.75, as determined by both chemical analysis and magnetic measurements. The electrochemical capability is discussed together with the structural and composition study.