Room Temperature Crystal Structure Research Articles

Phase evolution, defect chemistry, and electrical properties of Na0.5Bi0.5TiO3-BiNi0.5Ti0.5O3 solid solutions

Solid solutions of Na0.5Bi0.5TiO3 (NBT) and BiNi0.5Ti0.5O3 (BNiT) were prepared by a solid-state reaction route, and their electrical properties investigated by a combination of impedance spectroscopy and electromotive force measurements to explore the possibility of developing mixed ionic-electronic conductors based on NBT. Phase analysis showed that BNiT has a large solid solution limit in NBT (60 mol% based on X-ray diffraction), and the room temperature crystal structure changes from rhombohedral to pseudo-cubic with increasing BNiT content. Neutron diffraction revealed the coexistence of rhombohedral and tetragonal phases when the BNiT content ≥ 40 mol%. Electrically, incorporation of BNiT induces p-type electronic conduction into NBT by hopping of holes between Ni2+ (NiNix) and Ni3+ (NiNi·), and therefore changes the electrical conduction mechanism systematically from predominant oxide-ion conduction to mixed ionic-electronic conduction and then to predominant p-type electronic conduction. The total conductivity of the solid solutions showed a “V-shape” variation with increasing BNiT content. Possible mechanisms for the phase evolution and the conductivity-composition relationships are discussed. Achieving high levels of ionic and electronic conductivity simultaneously in NBT by introducing elements with variable oxidation states remains challenging due to the competition between an enhanced electronic component and a suppressed ionic component. Low levels of BNiT incorporation are, however, beneficial to reducing the dielectric loss of NBT for dielectric applications.

Crystallization and In Situ Room Temperature Data Collection Using the Crystallization Facility at Harwell and Beamline VMXi, Diamond Light Source.

Protocols for robotic protein crystallization using the Crystallization Facility at Harwell and in situ room temperature data collection from crystallization plates at Diamond Light Source beamline VMXi are described. This approach enables high-quality room-temperature crystal structures to be determined from multiple crystals in a straightforward manner and provides very rapid feedback on the results of crystallization trials as well as enabling serial crystallography. The value of room temperature structures in understanding protein structure, ligand binding, and dynamics is becoming increasingly recognized in the structural biology community. This pipeline is accessible to users from all over the world with several available modes of access. Crystallization experiments that are set up can be imaged and viewed remotely with crystals identified automatically using a machine learning tool. Data are measured in a queue-based system with up to 60° rotation datasets from user-selected crystals in a plate. Data from all the crystals within a particular well or sample group are automatically merged using xia2.multiplex with the outputs straightforwardly accessed via a web browser interface.

Magnetostructural Transformation and Magnetocaloric Properties of (Ni37.5Co12.5Mn35Ti15)100−xBx (x = 0.0 and 0.4) Melt-Spun Ribbons

The effect of B-doping on the martensitic transformation (MT), microstructure, room temperature (RT) crystal structure, and magnetocaloric properties of a typical all-d-metal Ni37.5Co12.5Mn35Ti15 quaternary alloy was studied by synthesizing melt-spun ribbon samples of nominal composition (Ni37.5Co12.5Mn35Ti15)100−xBx with x = 0.0 and 0.4. For B-free samples, SEM images show a grain-oriented microstructure formed by the columnar in shape-elongated grains with their major axis oriented along the thermal gradient during solidification. By contrast, the B-doped samples show smaller grains whose orientation tends to be perpendicular to the contact surface with the copper wheel. For all samples, austenite (AST) and martensite (MST) phases exhibited a cubic B2-type and 5M monoclinic crystal structure, respectively. The martensitic transition temperature (TM) and the Curie temperature of the austenite phase (TCA) were reduced from 295 K to 253 K and 333 K to 276 K, respectively, with the addition of B. The effect of thermal annealing for different times (from 30 min to 4 h) at 1073 K was studied. Thermal annealing increases the martensitic transformation temperature, whereas TCA remains unchanged. The maximum magnetic field-induced entropy changes |ΔST|max for B-doped samples were around 4.5 J kg−1 K−1 and 4.7 J kg−1 K−1 for as-solidified and annealed samples (1073 K–4 h), respectively, compared to that found for the undoped samples (i.e., ΔST = 16 J kg−1 K−1). However, the entropy reduction is accompanied by an increase in the full width at half-maximum of the ΔST(T) curve.

Cu-Content La1−XSrxNi1−YCuyO3−Δ Perovskites As Cobalt-Free Cathode Materials for High-Performance It-SOFCs

Solid Oxide Fuel Cells (SOFCs) are one of the most attractive energy conversion and storage devices, which can be applied for decentralized energy applications. However, the high operating temperature making SOFCs still unmarketable, which indicates that lowering the working temperature of SOFCs while still maintaining a high-power output is very crucial. For Intermediate-Temperature Solid Oxide Fuel Cells (IT-SOFCs), new cathode materials with high electrocatalytic activity and stability are necessary to provide a stable and high performance of cells. Perovskite-structured oxide (ABO3−δ) is one group of the most interesting material candidates for IT-SOFCs, presenting great potential in chemical composition modifications, yielding the design and gain of desired physicochemical and electrochemical properties [1]. The simple perovskite LaCuO3 is one of the well-studied Cu-content oxides with a high conductivity (106 S·cm−1), but it can be hardly obtained and suffers with stability issues in air [1, 2]. To stabilize the perovskite structure and to improve electrochemical properties of Cu-content oxides A-site and B-site modification strategy can be applied. It has been noted that Cu- and Ni-containing LaNi0.5Cu0.5O3−δ simple perovskite possesses low cathodic polarization of 0.056 Ω·cm2 at 800 °C, and a high power output of 870 mW·cm−2 at 900 °C [1, 3]. The generation of oxygen vacancies by strontium doping contributes to the increase of ionic conductivity component, and the Sr dopant can reduce the oxygen vacancy formation energy and increase the ionic conductivity of La1−xSrxMO3−δ (M = Fe, Mn) perovskites [1,4]. Therefore, in this work, Cu-content La1−xSrxNi1−yCuyO3−δ oxides with strontium doping at the A-site were evaluated as very promising Co-free cathode material candidates for IT-SOFCs.In this work, all La1−xSrxNi1−yCuyO3−δ compounds have been successfully obtained using soft chemistry. The room-temperature crystal structure of all oxides was assigned to the R-3c trigonal system. The substitution of La with Sr lowers the phase transition temperature from the R-3c space group to Pm-3m simple perovskite while increases the oxygen non-stoichiometry and the thermal expansion coefficient of studied materials. All investigated materials are chemically compatible with GDC-10, while unstable in contact with LSGM and 8YSZ. The manufactured anode-supported IT-SOFC with the La0.95Sr0.05Ni0.5Cu0.5O3−δ cathode presents an excellent power density of 445 mW·cm−2 at 650 °C in humidified H2. The results confirmed that La1−xSrxNi1−yCuyO3−δ perovskites can be potentially qualified as promising cathode candidates for IT-SOFCs, yielding promising electrochemical performance in the intermediate-temperature range [1].

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1−xCaLa0.5Er0.05Yb0.45(MoO4)3 Upconversion Scheelite-Type Phosphors

New triple molybdates LixNa1−xCaLa0.5(MoO4)3:Er3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) were manufactured successfully using the microwave-assisted sol-gel-based technique (MAS). Their room-temperature crystal structures were determined in space group I41/a by Rietveld analysis. The compounds were found to have a scheelite-type structure. In Li-substituted samples, the sites of big cations were occupied by a mixture of (Li, Na, La, Er, Yb) ions, which provided a linear cell volume decrease with the Li content increase. The increased upconversion (UC) efficiency and Raman spectroscopic properties of the phosphors were discussed in detail. The mechanism of optimization of upconversion luminescence upon Li content variation was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. The UC luminescence maximized at lithium content x = 0.05. The mechanism of UC optimization was shown to be due to the control of excitation/energy transfer channel, while the control of luminescence channels played a minor role. Over the whole spectral range, the Raman spectra of LixNa1−xCaLa0.5(MoO4)3 doped with Er3+ and Yb3+ ions were totally superimposed with the luminescence signal of Er3+ ions, and increasing the Li+ content resulted in the difference of Er3+ multiple intensity. The density functional theory calculations with the account for the structural disorder in the system of Li, Na, Ca, La, Er and Yb ions revealed the bandgap variation from 3.99 to 4.137 eV due to the changing of Li content. It was found that the direct electronic transition energy was close to the indirect one for all compounds. The determined chromaticity points (ICP) of the LiNaCaLa(MoO4)3:Er3+,Yb3+ phosphors were in good relation to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.

Unusual crystal structure evolution, multiple phase boundaries and phase coexistence in (1 - x)Ba(Cu1/3Nb2/3)O3-(x)PbTiO3 perovskite solid solution.

Exploring the functionalities of materials requires a profound understanding of the crystal structure. In this paper, room temperature crystal structures of a new solid solution (1 - x)Ba(Cu1/3Nb2/3)O3-(x)PbTiO3 have been investigated in the entire compositional span and different crystallographic phases and phase coexistence regions have been discovered. The confirmation of the symmetry of these crystal structures has been done with the help of Rietveld analysis of the high-resolution XRD data. Despite both the end components, Ba(Cu1/3Nb2/3)O3 and PbTiO3, having tetragonal (P4mm) symmetry, new cubic and monoclinic phases have been discovered for the intermediate compositions with multiple phase boundaries. The composition region 0.05 ≤ x ≤ 0.55 exhibits a cubic crystal structure and increasing PbTiO3 concentration to 0.62 results in a unique coexistence of two tetragonal phases with different tetragonalities. This transformation is mediated by coexisting cubic and tetragonal phases, for 0.59 and 0.60. The crystal structure of the solid solution later transforms into coexisting monoclinic and tetragonal phases for a wider compositional span i.e., 0.65 ≤ x ≤ 0.85. This composition region is very fascinating, as two phenomenologically different monoclinic structures have been observed in it. Finally, a tetragonal phase at x = 1 is achieved through the mediation of two coexisting tetragonal phases, for the region 0.85 < x ≤ 0.975. The evolution of different crystallographic structures and the coexisting phases are critically comprehended using the variations in the lattice parameters and unit cell volume. The presence of multiple phase boundaries spread across a wide range of compositions makes this solid solution very intriguing and a viable choice for exploring different properties with compositional tuning.

Evidence of a stable tetragonal (P4bm) phase in rhombohedral (R3c) complex perovskite (Na[formula omitted]Bi[formula omitted])[formula omitted]Ca[formula omitted]TiO[formula omitted] lead-free piezoelectric materials

The room temperature crystal structure and phase evolution of Ca-substituted Na1/2Bi1/2TiO3(NBCT) at A-site were investigated systematically using X-ray diffraction (XRD) combined with Raman spectroscopy. While XRD patterns of calcined powders exhibited the expected rhombohedral (R3c) phase at room temperature due to low Ca concentration, the corresponding sintered samples displayed peak splitting for all Bragg peaks, appearing as shoulders for all studied compositions. This departure from the average rhombohedral (R3c) to a non-rhombohedral structure is an indication of a new phase evolution of this system. The optimal Rietveld refinement corresponds to the coexistence of two phases, rhombohedral and tetragonal (R3c+P4bm) in the equilibrium state at room temperature. The proposed model describes the growth of a stable high-temperature tetragonal (P4bm) phase within the rhombohedral (R3c) matrix at room temperature. This work is the first XRD macroscale detection of a stable tetragonal (P4bm) phase in rhombohedral complex perovskite at room temperature.

Autoprocessing and oxyanion loop reorganization upon GC373 and nirmatrelvir binding of monomeric SARS-CoV-2 main protease catalytic domain

The monomeric catalytic domain (residues 1–199) of SARS-CoV-2 main protease (MPro1-199) fused to 25 amino acids of its flanking nsp4 region mediates its autoprocessing at the nsp4-MPro1-199 junction. We report the catalytic activity and the dissociation constants of MPro1-199 and its analogs with the covalent inhibitors GC373 and nirmatrelvir (NMV), and the estimated monomer-dimer equilibrium constants of these complexes. Mass spectrometry indicates the presence of the accumulated adduct of NMV bound to MProWT and MPro1-199 and not of GC373. A room temperature crystal structure reveals a native-like fold of the catalytic domain with an unwound oxyanion loop (E state). In contrast, the structure of a covalent complex of the catalytic domain-GC373 or NMV shows an oxyanion loop conformation (E* state) resembling the full-length mature dimer. These results suggest that the E-E* equilibrium modulates autoprocessing of the main protease when converting from a monomeric polyprotein precursor to the mature dimer.

Synthesis and crystal structure of topiramate azido-sulfate at 90 K and 298 K.

The low (90 K) and room (298 K) temperature crystal structures of topiramate azido-sulfate [systematic name 2,3:4,5-bis-O-(1-methyl-ethyl-idene)-β-d-fructo-pyran-ose azido-sulfate], C12H19N3O8S, an inter-mediate in the synthesis of the anti-convulsant drug topiramate, are described. Topiramate azido-sulfate (I) finds use as a reference impurity standard for topiramate. A modified synthesis and some spectroscopic details are also presented.

Pressure induced structural phase transition in Cr doped Mn2O3 multiferroics

The pressure dependent structural properties of polycrystalline Mn2−xCrxO3 (x = 0, 0.01, 0.05) multiferroics have been investigated using synchrotron x-ray diffraction (SXRD) measurements up to 41 GPa at room temperature (RT). Our results illustrate that irrespective of their RT crystal structure, all the studied samples undergo pressure induced structural phase transition to monoclinic phase. For pristine Mn2O3, the phase transition starts around 20.8 GPa and completely transformed to monoclinic phase around 37 GPa during compression. The co-existence of orthorhombic and monoclinic phase persists at wide pressure range i.e. 20.8 to 37 GPa. The Cr substitutions lower the required pressure for pressure induced phase transition i.e. for x = 0.01 and x = 0.05, Cr doped samples, the pressure induced phase transition occurs at 35 GPa and 33 GPa, respectively. These transitions are reversible (with hysteresis) during decompression and remained unquenchable under pressure. These results corroborate that Cr substitution modify the RT crystal structure and induces positive chemical pressure in Mn2O3.

Structural basis for receptor selectivity and inverse agonism in S1P5 receptors

The bioactive lysophospholipid sphingosine-1-phosphate (S1P) acts via five different subtypes of S1P receptors (S1PRs) - S1P1-5. S1P5 is predominantly expressed in nervous and immune systems, regulating the egress of natural killer cells from lymph nodes and playing a role in immune and neurodegenerative disorders, as well as carcinogenesis. Several S1PR therapeutic drugs have been developed to treat these diseases; however, they lack receptor subtype selectivity, which leads to side effects. In this article, we describe a 2.2 Å resolution room temperature crystal structure of the human S1P5 receptor in complex with a selective inverse agonist determined by serial femtosecond crystallography (SFX) at the Pohang Accelerator Laboratory X-Ray Free Electron Laser (PAL-XFEL) and analyze its structure-activity relationship data. The structure demonstrates a unique ligand-binding mode, involving an allosteric sub-pocket, which clarifies the receptor subtype selectivity and provides a template for structure-based drug design. Together with previously published S1PR structures in complex with antagonists and agonists, our structure with S1P5-inverse agonist sheds light on the activation mechanism and reveals structural determinants of the inverse agonism in the S1PR family.

Evaluation of Cu-substituted La1.5Sr0.5NiO4+δ as air electrode for CO2 electrolysis in solid oxide electrolysis cells

Ruddlesden-Popper oxide, Cu-substituted La1.5Sr0.5NiO4+δ series materials (La1.5Sr0.5Ni1-xCuxO4+δ; denoted as LSNCux; x = 0, 0.1, 0.25, 0.5) are investigated as air electrodes in solid oxide electrolysis cells (SOECs) for electrolysis of CO2. Room temperature crystal structure, electrical conductivity and oxygen exchange capacity, as well as electrochemical performance of LSNCux are comprehensively investigated. Among the series of samples, LSNCu0.25 half-cell exhibits the lowest polarization resistance value of 0.179 Ω cm2 at 800 °C, which decreases by approximately 86.07% compared with that of LSN. In addition, the fuel electrode-supported single cell with LSNCu0.25 air electrode presents a high current density of 1.2 A cm−2 at 1.5 V under 30% CO–70% CO2 condition at 800 °C, which is 207% of LSN (0.58 A cm−2) under the same condition. Results show that the impressive catalytic activity for oxygen evolution reaction (OER) is ascribed to the improved electronic conductivity and oxygen exchange capacity. With Cu substitution for Ni-site, the contraction of Ni–O bond in NiO6 octahedron and increased concentration of charge carries owing to the oxidation of Ni2+ to Ni3+ are beneficial to the electron conduction. The formation of more interstitial oxygen as ionic compensation also favors the oxygen ion diffusion/exchange and greatly accelerates the charge transfer process. Furthermore, no degradation is observed for the single cell durability test at 750 °C for 50 h, which demonstrates the highly stable performance of LSNCu0.25 air electrode for electrolysis of CO2.

Combination of an inject-and-transfer system for serial femtosecond crystallography.

Serial femtosecond crystallography (SFX) enables the determination of room-temperature crystal structures of macromolecules with minimized radiation damage and provides time-resolved molecular dynamics by pump-probe or mix-and-inject experiments. In SFX, a variety of sample delivery methods with unique advantages have been developed and applied. The combination of existing sample delivery methods can enable a new approach to SFX data collection that combines the advantages of the individual methods. This study introduces a combined inject-and-transfer system (BITS) method for sample delivery in SFX experiments: a hybrid injection and fixed-target scanning method. BITS allows for solution samples to be reliably deposited on ultraviolet ozone (UVO)-treated polyimide films, at a minimum flow rate of 0.5 nl min-1, in both vertical and horizontal scanning modes. To utilize BITS in SFX experiments, lysozyme crystal samples were embedded in a viscous lard medium and injected at flow rates of 50-100 nl min-1 through a syringe needle onto a UVO-treated polyimide film, which was mounted on a fixed-target scan stage. The crystal samples deposited on the film were raster scanned with an X-ray free electron laser using a motion stage in both horizontal and vertical directions. Using the BITS method, the room-temperature structure of lysozyme was successfully determined at a resolution of 2.1 Å, and thus BITS could be utilized in future SFX experiments.

Michaelis-like complex of SARS-CoV-2 main protease visualized by room-temperature X-ray crystallography.

SARS-CoV-2 emerged at the end of 2019 to cause an unprecedented pandemic of the deadly respiratory disease COVID-19 that continues to date. The viral main protease (Mpro) is essential for SARS-CoV-2 replication and is therefore an important drug target. Understanding the catalytic mechanism of Mpro, a cysteine protease with a catalytic site comprising the noncanonical Cys145-His41 dyad, can help in guiding drug design. Here, a 2.0 Å resolution room-temperature X-ray crystal structure is reported of a Michaelis-like complex of Mpro harboring a single inactivating mutation C145A bound to the octapeptide Ac-SAVLQSGF-CONH2 corresponding to the nsp4/nsp5 autocleavage site. The peptide substrate is unambiguously defined in subsites S5 to S3' by strong electron density. Superposition of the Michaelis-like complex with the neutron structure of substrate-free Mpro demonstrates that the catalytic site is inherently pre-organized for catalysis prior to substrate binding. Induced fit to the substrate is driven by P1 Gln binding in the predetermined subsite S1 and rearrangement of subsite S2 to accommodate P2 Leu. The Michaelis-like complex structure is ideal for in silico modeling of the SARS-CoV-2 Mpro catalytic mechanism.

Role of Active Site Loop Dynamics in Mediating Ligand Release from E. coli Dihydrofolate Reductase.

Conformational fluctuations from ground-state to sparsely populated but functionally important excited states play a key role in enzyme catalysis. For Escherichia coli dihydrofolate reductase (DHFR), the release of the product tetrahydrofolate (THF) and oxidized cofactor NADP+ occurs through exchange between closed and occluded conformations of the Met20 loop. A "dynamic knockout" mutant of E. coli DHFR, where the E. coli sequence in the Met20 loop is replaced by the human sequence (N23PP/S148A), models human DHFR and is incapable of accessing the occluded conformation. 1H and 15N CPMG relaxation dispersion analysis for the ternary product complex of the mutant enzyme with NADP+ and the product analogue 5,10-dideazatetrahydrofolate (ddTHF) (E:ddTHF:NADP+) reveals the mechanism by which NADP+ is released when the Met20 loop cannot undergo the closed-to-occluded conformational transition. Two excited states were observed: one related to a faster, relatively high-amplitude conformational fluctuation in areas near the active site, associated with the shuttling of the nicotinamide ring of the cofactor out of the active site, and the other to a slower process where ddTHF undergoes small-amplitude motions within the binding site that are consistent with disorder observed in a room-temperature X-ray crystal structure of the N23PP/S148A mutant protein. These motions likely arise due to steric conflict of the pterin ring of ddTHF with the ribose-nicotinamide moiety of NADP+ in the closed active site. These studies demonstrate that site-specific kinetic information from relaxation dispersion experiments can provide intimate details of the changes in catalytic mechanism that result from small changes in local amino acid sequence.

Stable sample delivery in a viscous medium via a polyimide-based single-channel microfluidic chip for serial crystallography

Serial crystallography (SX) provides room-temperature crystal structures with minimal radiation damage and facilitates the comprehension of molecular dynamics through time-resolved studies. In SX experiments, it is important to deliver a large number of crystal samples to the X-ray interaction point in a serial and stable manner. The advantage of crystal delivery in a viscous medium via a capillary is the ability to deliver all of the crystal samples to the X-ray interaction point at a low flow rate; however, the capillary often breaks during handling and high X-ray absorption can occur at low energy states. This study aimed to develop a stable system for sample delivery in a viscous medium via a polyimide-based single-channel microfluidic (PSM) chip for SX. Since this microfluidic chip comprises a polyimide film, it has high tensile strength and higher X-ray transmittance than a quartz capillary. The PSM chip was connected to a syringe containing the microcrystals embedded in viscous medium. The channel of the PSM chip was aligned to the X-ray path, and the viscous medium containing lysozyme crystals was stably delivered using a syringe pump at a flow rate of 100 nl min−1. Room-temperature lysozyme crystal structures were successfully determined at 1.85 Å resolution. This method would greatly facilitate sample delivery for SX experiments using synchrotron X-rays.

Magnetic ground state and crystal structure of the giant dielectric constant material Ba(Fe1/2Nb1/2)O3

The room temperature crystal structure as well as the magnetic ground state of Ba(Fe1/2Nb1/2)O3 (BFN) are controversial. The results of Rietveld refinements using high-resolution synchrotron x-ray powder diffraction (SXRPD) data are presented to show that BFN belongs to cubic perovskite structure in the Pm3¯m space group and not in the cubic Fm3¯m or monoclinic symmetries, proposed by some earlier workers based on the analysis of the laboratory source XRD data. The temperature dependent specific heat measurements in the 1.8 to 300 K range on well characterized BFN samples are presented to show the absence of any long-range ordered (LRO) antiferromagnetic (AFM) transition, proposed by some earlier workers based on the observation of a peak in the temperature dependence of zero-field cooled (ZFC) DC magnetization around 25 to 32 K. Results of temperature dependent magnetization measurements during warming cycle on ZFC and field cooled (FC) BFN samples reveal history dependent bifurcation with a peak in the ZFC M (T) curve at Tf ~ 29 K, in agreement with some previous results where it was attributed to a spin-glass transition even though such an irreversibility can result from superparamagnetic (SPM) blocking as well. The appearance of a short plateau in our FC M (T) curve below Tf suggests a cluster spin-glass phase of BFN below Tf. This was confirmed by us through the ac susceptibility χ' (T, ω) studies which reveal divergence of spin dynamics at the spin-glass transition temperature TSG ~ (28 ± 1) K with a large characteristic spin relaxation time τ0 ~ 10−6 s following Vogel-Fulcher as well as power-law type critical dynamics. The existence of the magnetic glassy state in BFN is further supported by the observation of (1) magnetic field dependent shift of Tf with increasing magnetic field along the de Almeida-Thouless line in the T-H plane with a characteristic exponent of m = 2/3, (2) weak remanent magnetization Mr below Tf with exponentially decreasing Mr on approaching Tf, (3) extremely slow decay of the thermoremanent magnetization below Tf with time as per a stretched exponential function, and (4) characteristic aging, rejuvenation and memory effects below Tf. These results provide the first unambiguous confirmation of the cluster spin-glass state of BFN and settle the existing controversies related to its magnetic ground state.

Ferroelectric transition and structural modulation in Sr2Na(Nb1−xTax)5O15 tungsten bronze ceramics

Effects of B-site Ta5+ substitution on the ferroelectric transition and crystal structure modulation were investigated for Sr2Na(Nb1−xTax)5O15 (x = 0–0.5) tungsten bronzes. The weakened ferroelectricity and enhanced relaxor behaviors were observed with increasing Ta, while the room temperature crystal structure changed from non-centrosymmetric to centrosymmetric. Raman spectra showed a decreasing intensity of the internal vibrations with increasing Ta, revealing different bonding mechanisms between Nb/Ta cations and O anions with reduced covalence by Ta-substitution, which resulted in weakened polarization. Two sets of superlattice reflections were detected in the selected area electron diffraction patterns: commensurate modulation for all compositions (type I), described by the wave vectors q1=14(a0∗+b0∗)+12c0∗ and q2=12(a0∗+b0∗); extra reflections of 1/2[0 0 l] at some local areas for Ta-containing compositions (type II), indicating the possible ordering of B-site cations. The distinct bonding state between the B-site cation and the O anion dominates the crossover from ferroelectric to relaxor behaviors in the present compounds.

Combining X-rays, neutrons and electrons, and NMR, for precision and accuracy in structure-function studies.

The distinctive features of the physics-based probes used in understanding the structure of matter focusing on biological sciences, but not exclusively, are described in the modern context. This is set in a wider scope of holistic biology and the scepticism about `reductionism', what is called the `molecular level', and how to respond constructively. These topics will be set alongside the principles of accuracy and precision, and their boundaries. The combination of probes and their application together is the usual way of realizing accuracy. The distinction between precision and accuracy can be blurred by the predictive force of a precise structure, thereby lending confidence in its potential accuracy. These descriptions will be applied to the comparison of cryo and room-temperature protein crystal structures as well as the solid state of a crystal and the same molecules studied by small-angle X-ray scattering in solution and by electron microscopy on a sample grid. Examples will include: time-resolved X-ray Laue crystallography of an enzyme Michaelis complex formed directly in a crystal equivalent to in vivo; a new iodoplatin for radiation therapy predicted from studies of platin crystal structures; and the field of colouration of carotenoids, as an effective assay of function, i.e. their colouration, when unbound and bound to a protein. The complementarity of probes, as well as their combinatory use, is then at the foundation of real (biologically relevant), probe-artefacts-free, structure-function studies. The foundations of our methodologies are being transformed by colossal improvements in technologies of X-ray and neutron sources and their beamline instruments, as well as improved electron microscopes and NMR spectrometers. The success of protein structure prediction from gene sequence recently reported by CASP14 also opens new doors to change and extend the foundations of the structural sciences.

A 35-year-old mystery solved: a facile synthetic route and structural confirmation of tetrachlorobis(diethyl ether)tungsten(IV)

The true identity of the diethyl ether adduct of tungsten(IV) chloride, WCl4(Et2O)x, has been in doubt since 1985. Initially postulated as the bis-adduct, WCl4(Et2O)2, questions arose when elemental analyses were more in line with a mono-ether adduct, viz. WCl4(Et2O). It was proposed that this was due to the thermal instability of the bis-adduct. Here, we report the room-temperature X-ray crystal structure and Hirshfeld surface characteristics of trans-tetrachloridobis(diethyl ether)tungsten(IV), trans-WCl4(Et2O)2 or trans-[WCl4(C4H10O)2]. The compound crystallizes, with half of the molecule in the asymmetric unit, in the centrosymmetric space group P21/n. The W-O distance is 2.070 (2) Å, while the W-Cl distances are 2.3586 (10) and 2.3554 (10) Å.