Oxide Ion and Proton Conductivity in a Family of Highly Oxygen-Deficient Perovskite Derivatives.

Functional oxides showing high ionic conductivity have many important technological applications. We report oxide ion and proton conductivity in a family of perovskite-related compounds of the general formula A3OhTd2O7.5, where Oh is an octahedrally coordinated metal ion and Td is a tetrahedrally coordinated metal ion. The high tetrahedral content in these ABO2.5 compositions relative to that in the perovskite ABO3 or brownmillerite A2B2O5 structures leads to tetrahedra with only three of their four vertices connected in the polyhedral framework, imparting a potential low-energy mechanism for O2- migration. The low- and high-temperature average and local structures of Ba3YGa2O7 (P2/c, a = 7.94820(5) Å, b = 5.96986(4) Å, c = 18.4641(1) Å, and ß = 91.2927(5) ° at 22 °C) were determined by Rietveld and neutron pair distribution function (PDF) analysis, and a phase transition to a high-temperature P1121/a structure (a = 12.0602(1) Å, b = 9.8282(2) Å, c = 8.04982(6) Å, and γ = 107.844(3)° at 1000 °C) involving the migration of O2- ions was identified. Ionic conductivities of Ba3YGa2O7.5 and compositions substituted to introduce additional oxide vacancies and interstitials are reported. Most phases show proton conductivity at lower temperatures and oxide ion conductivity at high temperatures, with Ba3YGa2O7.5 retaining proton conductivity at high temperatures. Ba2.9La0.1YGa2O7.55 and Ba3YGa1.9Ti0.1O7.55 appear to be dominant oxide ion conductors, with conductivities an order of magnitude higher than that of the parent compound.

Understanding the Correlation between Oxide Ion Mobility and Site Distributions in Ba3NbWO8.5.

A correlation between oxygen site distributions and ionic conductivity has been established in the recently discovered family of oxide-ion conductors Ba3M2O8.5±Î´ (M = Nb, V, Mo, W). We rationalize this observation on the basis of structural insights gained from the first single-crystal neutron diffraction data collected for a member of this family, Ba3NbWO8.5, and theoretical considerations of bonding and O site energies.

Insight into Design of Improved Oxide Ion Conductors: Dynamics and Conduction Mechanisms in the Bi0.913V0.087O1.587 Solid Electrolyte.

Extensive quasielastic neutron scattering measurements have been used to directly observe oxide ion dynamics on the nanosecond time scale in bismuth vanadate with formula Bi0.913V0.087O1.587, which exhibits remarkable oxide ion conductivity at low temperatures. This is the longest time scale neutron scattering study of any fluorite-type solid electrolyte, and it represents only the second case of oxide ion dynamics in any material observed on a nanosecond time scale by quasielastic neutron scattering. Ab initio molecular dynamics simulations reveal two mechanisms that contribute to the oxide ion dynamics in the material: a slower diffusion process through the Bi-O sublattice and a faster process which corresponds to more localized dynamics of the oxide ions within the VO x coordination spheres. The length of the trajectories simulated and the validation of the simulations by neutron scattering experiments provide for the first time a quantitative insight into the relative contributions of the two processes to the oxide ion conduction in this exceptional solid electrolyte, which can be used to derive design principles for the preparation of related oxide ion conductors with even better properties.

Average and Local Structure of Apatite-Type Germanates and Implications for Oxide Ion Conductivity.

Materials with the apatite structure have a range of important applications in which their function is influenced by details of their local structure. Here, we describe an average and local structural study to probe the origins of high-temperature oxide ion mobility in La10(GeO4)6O3 and La8Bi2(GeO4)6O3 oxygen-excess materials, using the low-conductivity interstitial oxide-free La8Sr2(GeO4)6O2 as a benchmark. For La10 and La8Bi2, we locate the interstitial oxygen, Oint, responsible for conductivity by Rietveld refinement and relate the P63/m to P1̅ phase transitions on cooling to oxygen ordering. Local structural studies using neutron total scattering reveal that well-ordered GeO5 square pyramidal groups form in the structure at low temperature, but that Oint becomes significantly more disordered in the high-conductivity, high-temperature structures, with a transition to more trigonal-bipyramid-like average geometry. We relate the higher conductivity of Bi materials to the presence of several Oint sites of similar energy in the structure, which correlates with its less-distorted low-temperature average structure.

Understanding the Behavior of the Above-Room-Temperature Molecular Ferroelectric 5,6-Dichloro-2-methylbenzimidazole Using Symmetry Adapted Distortion Mode Analysis.

The exploitable properties of many functional materials are intimately linked with symmetry-changing phase transitions. These include properties such as ferroelectricity, second harmonic generation, conductivity, magnetism and many others. We describe a new symmetry-inspired method for systematic and exhaustive evaluation of the symmetry changes possible in molecular systems using molecular distortion modes, and how different models can be automatically tested against diffraction data. The method produces a quantitative structural landscape from which the most appropriate structural description of a child phase can be chosen. It can be applied to any molecular or molecular-fragment containing material where a (semi) rigid molecule description is appropriate. We exemplify the method on 5,6-dichloro-2-methylbenzimidazole (DC-MBI), an important molecular ferroelectric. We show that DC-MBI undergoes an unusual symmetry-lowering transition on warming from orthorhombic Pca21 ( T ≲ 400 K) to monoclinic Pc. Contrary to expectations, the high temperature phase of DC-MBI remains polar.

An Exhaustive Symmetry Approach to Structure Determination: Phase Transitions in Bi2Sn2O7.

The exploitable properties of many materials are intimately linked to symmetry-lowering structural phase transitions. We present an automated and exhaustive symmetry-mode method for systematically exploring and solving such structures which will be widely applicable to a range of functional materials. We exemplify the method with an investigation of the Bi2Sn2O7 pyrochlore, which has been shown to undergo transitions from a parent γ cubic phase to ß and α structures on cooling. The results include the first reliable structural model for ß-Bi2Sn2O7 (orthorhombic Aba2, a = 7.571833(8), b = 21.41262(2), and c = 15.132459(14) Å) and a much simpler description of α-Bi2Sn2O7 (monoclinic Cc, a = 13.15493(6), b = 7.54118(4), and c = 15.07672(7) Å, ß = 125.0120(3)°) than has been presented previously. We use the symmetry-mode basis to describe the phase transition in terms of coupled rotations of the Bi2O' anti-cristobalite framework, which allow Bi atoms to adopt low-symmetry coordination environments favored by lone-pair cations.

Computational Insights into Dion-Jacobson Type Oxide Ion Conductors.

Dion-Jacobson type materials have recently emerged as a new structural family of oxide ion conductors, materials important for applications in a variety of electrochemical devices. While some attempts to improve their ionic conductivity have been reported, a detailed understanding of the underlying oxide ion diffusion mechanisms in these materials is still missing. To explore the structure-property relationships leading to the favorable properties, we carried out ab initio molecular dynamics simulations of oxide ion diffusion in CsBi2Ti2NbO10-δ. Our computational study reveals significant out-of-plane dynamics, indicating that the dominant pathway for oxide ion migration is via jumps into and out of the (ab) crystallographic plane. This suggests that further improvement of oxide ion conductivity relative to CsBi2Ti2NbO10-δ could be achieved by enhancing the rotational flexibility of the coordination polyhedra located in the inner perovskite layer, thereby facilitating faster out-of-plane motions.

Systematic and controllable negative, zero, and positive thermal expansion in cubic Zr(1-x)Sn(x)Mo2O8.

We describe the synthesis and characterization of a family of materials, Zr1-xSnxMo2O8 (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, αl, ranging from -7.9(2) × 10(-6) to +5.9(2) × 10(-6) K(-1) (12-500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of "cubic" SnMo2O8, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material.

Oxide Ion Conductivity, Proton Conductivity, and Phase Transitions in Perovskite-Derived Ba3-x Sr x YGa2O7.5 0 ≤ x ≤ 3 Materials.

We report the synthesis, structural characterization, and oxide ion and proton conductivities of the perovskite-related Ba3-x Sr x YGa2O7.5 family. Single-phase samples are prepared for 0 ≤ x ≤ 3 and show a complex structural evolution from P2/c to C2 space groups with an increase in x. For 1.0 ≲ x ≲ 2.4, average structures determined by X-ray and neutron powder diffraction show metrically orthorhombic unit cells, but HAADF-STEM imaging reveals this is caused by microstructural effects due to intergrowths of the Ba- and Sr-rich structure types. Variable-temperature powder diffraction studies suggest that 0 ≲ x ≲ 2.4 compositions undergo a phase transition upon being heated to space group Cmcm that involves disordering of the oxygen substructure. Thermal expansion coefficients are reported for the series. Complex impedance studies show that the Ba-rich samples are mixed proton and oxide ion conductors under moist atmospheres but are predominantly oxide ion conductors at high temperatures or under dry atmospheres. Sr-rich samples show significantly less water uptake and appear to be predominantly oxide ion conductors under the conditions studied.

Complex superstructures of Mo2P4O15.

We report structural studies on Mo(2)P(4)O(15) over the temperature range 16-731 K, which show that it is considerably more complex than revealed by earlier work. Its low-temperature structure has lattice parameters a = 24.1134(6) A, b = 19.5324(5) A, c = 25.0854(6) A, beta = 100.015(1) degrees, and V = 11635.0(5) A(3) at 120 K, containing 441 unique atoms in space group Pn, a remarkably high number for a material with such a simple composition. Mo(2)P(4)O(15) undergoes a structural phase transition at approximately 520 K to a high-temperature phase in space group P1, with lattice parameters a = 17.947(3) A, b = 19.864(3) A, c = 21.899(3) A, alpha = 72.421(3) degrees, beta = 78.174(4) degrees, gamma = 68.315(4) degrees, and V = 6877.2(19) A(3) at 573 K. The high-temperature structure, with 253 unique atoms, retains much of the low-temperature complexity.

Brownmillerite-Type Sr2ScGaO5 Oxide Ion Conductor: Local Structure, Phase Transition, and Dynamics.

Brownmillerite-type Sr2ScGaO5 has been investigated by a range of experimental X-ray and neutron scattering techniques (diffraction, total scattering, and spectroscopy) and density functional theory calculations in order to characterize its structure and dynamics. The material undergoes a second-order phase transition on heating during which a rearrangement of the (GaO4/2)∞ tetrahedral chains occurs, such that they change from being essentially fully ordered in a polar structure at room temperature to being orientationally disordered above 400 °C. Pair distribution function analysis carried out using neutron total scattering data suggests that GaO4 tetrahedra remain as fairly rigid units above and below this transition, whereas coordination polyhedra in the (ScO6/2)∞ layers distort more. Inelastic neutron scattering and phonon calculations reveal the particular modes that are associated with this structural change, which may assist ionic conductivity in the material at higher temperatures. On the basis of the correlations between these findings and the measured conductivity, we have synthesized a derivative compound with increased conductivity and suggest a possible conduction mechanism in these brownmillerite-type solid electrolytes.

Structural study of polymorphs and solvates of finasteride.

NMR and XRD data are reported for several new forms of finasteride, including the results of complete structure determinations for three solvates. Form III of finasteride, hitherto only mentioned in the patent literature, and a new anhydrous form designated Form X, have been found in mixtures of polymorphs and their (13)C NMR chemical shifts obtained. The results demonstrate that the crystallographic asymmetric units contain three molecules and one molecule, respectively. Attempts to reproduce "Form H1", as described in a patent, resulted in a new IPA solvate hydrate. The previously-reported acetic acid, dioxane, and ethyl acetate solvates have been further characterised, and new THF and diethyl ether solvates prepared and characterised. The crystal structures of the dioxane, IPA, and THF solvates have been determined by single-crystal X-ray diffraction. All the solvates (except the acetic acid case) are found to be hemihydrates, to have a finasteride: solvent molar ratio of 2:1 and to have a common structure. The solvate molecules are highly disordered and sited in channels in the structure. The powder XRD patterns are characteristic of the common structure. These solvates may be distinguished by the characteristic CPMAS (13)C signals from the solvent molecules, but the resonances of the host finasteride structures differ only marginally, and powder XRD patterns are almost indistinguishable. Magic-angle spinning (MAS) proton spectra give sharp lines for the solvent peaks, confirming their high degree of mobility. This is further shown in one case by direct polarisation (13)C spectra. Mobility of the tert-butyl group is also implied. Thermal characteristics have been studied and TGA used (in conjunction with solution-state proton NMR) to estimate molar ratios.

Structure and physicochemical characterization of a naproxen-picolinamide cocrystal.

Naproxen (NPX) is a nonsteroidal anti-inflammatory drug with pain- and fever-relieving properties, currently marketed in the sodium salt form to overcome solubility problems; however, alternative solutions for improving its solubility across all pH values are desirable. NPX is suitable for cocrystal formation, with hydrogen-bonding possibilities via the COOH group. The crystal structure is presented of a 1:1 cocrystal of NPX with picolinamide as a coformer [systematic name: (S)-2-(6-methoxynaphthalen-2-yl)propanoic acid-pyridine-2-carboxamide (1/1), C14H14O3·C6H6N2O]. The pharmaceutically relevant physical properties were investigated and the intrinsic dissolution rate was found to be essentially the same as that of commercial naproxen. An NMR crystallography approach was used to investigate the H-atom positions in the two crystallographically unique COOH-CONH hydrogen-bonded dimers. 1H solid-state NMR distinguished the two carboxyl protons, despite the very similar crystallographic environments. The nature of the hydrogen bonding was confirmed by solid-state NMR and density functional theory calculations.

Na(+) mobility in sodium strontium silicate fast ion conductors.

We present the first direct evidence of Na-ion mobility in sodium strontium silicate fast ion conductors, based on variable temperature (23)Na solid state NMR spectroscopy and spin-lattice relaxation measurements.

Mo2P4O15--the most complex oxide structure solved by single crystal methods?

We report the crystal structure and phase transitions of Mo2P4O15 which, despite a simple chemical formula, has 441 crystallographically unique atoms in its asymmetric unit and thus has the most complex structure of any extended oxide reported to date.

Light induced excited high spin-state trapping in [FeL2](BF4)2 (L = 2,6-di(pyrazol-1-yl)pyridine).

The spin-crossover complex [FeL2](BF4)2 undergoes a LIESST transition at 30 K on irradiation; the structures of the low-spin ground and high-spin metastable states at this temperature are presented.

[R,S]-Ethambutol dihydrochloride: variable-temperature studies of a dimorphic system with very similar packing.

The two polymorphs (Forms I and II) of [R,S]-ethambutol dihydrochloride transform enantiotropically and reversibly in a single-crystal-to-single-crystal phase transformation mode. These structurally very similar forms have been characterized and their thermodynamic relationship has been investigated by variable-temperature solid-state carbon-13 nuclear magnetic resonance, variable-temperature powder X-ray diffraction, differential scanning calorimetry, and optical microscopy. The nuclear magnetic resonance results are compared with those for the two polymorphs of the [S,S] diastereomer with known structures.

Synthesis, structural and spectroscopic characterization, in vitro cytotoxicity and in vivo activity as free radical scavengers of chlorido(p-cymene) complexes of ruthenium(II) containing N-alkylphenothiazines.

Three new ruthenium(II) complexes 1-3 containing N-alkylphenothiazine molecules were synthesized by reaction of [RuCl(2)(η(6)-p-cymene)](2) with chlorpromazine hydrochloride (1), trifluoperazine dihydrochloride (2) or thioridazine hydrochloride (3). The compounds of the general formula L[RuCl(3)(η(6)-p-cymene)] were characterized by elemental analysis and spectroscopic methods (FT-IR, UV-Vis, (1)H and (13)C NMR). Complex 2 was structurally characterized by single crystal X-ray diffraction. In vitro cytotoxic activity of complexes 1-3 were assayed in four human carcinoma cell lines MCF-7, MDA-MB-453 (breast carcinoma), SW-480 (colon carcinoma) and IM9 (myeloma multiple cells). The highest cytotoxicity (12.1 ≤ IC(50) ≤ 17.3 µM) and induced a total (SW-480) or almost total cell death (MCF-7, MDA-MB-453) at 25 µM in 48 h of treatment were observed for complex 2. The influence of three different doses (0.4, 4.5 and 90.4 µM/kg bw) of complex 2 on activities of antioxidants enzymes (superoxide dismutase (SOD) and catalase (CAT)) and lactate dehydrogenase (LDH) were investigated under physiological conditions. The effects on nitrite production (NO(2)(-)) and level of erythrocytes malondialdehyde (MDA) in rats blood were evaluated, too.

Structural chemistry of (PPh4)2M(WS4)2 materials.

In this paper we discuss the structural chemistry of (PPh(4))(2)M(WS(4))(2) (M = Co, Ni, Zn) materials. For M = Ni we and others have been unable to grow single crystals and we report the structure determination from powder diffraction. The material is triclinic (P1, a = 9.3730(2), b = 12.4951(3), c = 12.5189(3) A, alpha = 65.814(1), beta = 83.751(1), gamma = 69.571(1) degrees at T = 293 K). It contains square-planar coordination around Ni. For M = Zn we have isolated two polymorphs. We describe new analysis of the complex superstructure and diffuse scattering observed in the tetragonal polymorph (I4, a = 18.723(4), c = 13.563(4) A at T = 120 K) and the bulk preparation of a monoclinic (P2(1)/c, a = 18.6397(4), b = 15.3693(5), c = 18.9822(5) A, beta = 109.239(2) degrees at T = 293 K) polymorph isostructural with the M = Co material.