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The coordination of benzene-1,3,5-tribenzoate (BTB) and imidazole (Im) with cobalt under basic conditions yields a 2D layered structure, Co 3 (BTB) 1.5 (Im) 1.35 (O) 0.5 (OH) 0.5 (H 2 O) 1.65 guests ( 1 ), in which the imidazoles are weakly π–π stacked and hydrogen bonded to the adjacent layers affording a 3D supramolecular network. The structure is based on a hexanuclear Co 6 building unit which comprises four octahedral and two tetrahedral Co(II) centres. The framework is permanently porous to N 2 , CO 2 and CH 4 , with the strength of interaction at zero coverage being comparable to that at high loading.

Pulsed laser deposition has been used to artificially construct the n = 3 Ruddlesden Popper structure La2Sr2Mn3O10 in epitaxial thin film form by sequentially layering La1-xSrxMnO3 and SrO unit cells aided by in situ reflection high energy electron diffraction monitoring. The interval deposition technique was used to promote two-dimensional SrO growth. X-ray diffraction and cross-sectional transmission electron microscopy indicated that the trilayer structure had been formed. A site ordering was found to differ from that expected thermodynamically, with the smaller Sr2+ predominantly on the R site due to kinetic trapping of the deposited cation sequence. A dependence of the out-of-plane lattice parameter on growth pressure was interpreted as changing the oxygen content of the films. Magnetic and transport measurements on fully oxygenated films indicated a frustrated magnetic ground state characterized as a spin glass-like magnetic phase with the glass temperature T-g approximate to 34 K. The magnetic frustration has a clear in-plane (ab) magnetic anisotropy, which is maintained up to temperatures of 150 K. Density functional theory calculations suggest competing antiferromagnetic and ferromagnetic long-range orders, which are proposed as the origin of the low-temperature glassy state.

Deposition of nanosized layers of two different metal oxides upon one another produces layered heterostructures with a wide range of new physical properties.1 For example, a conducting two-dimensional electron gas was discovered at the interface between the two insulators LaAlO3 and SrTiO3.2 The atomic arrangements within heterostructures of complex functional oxides determine the resulting properties and are not necessarily straightforward to construct based on the bulk crystal structures of the independent components.

Combining long-range magnetic order with polarity in the same structure is a prerequisite for the design of (magnetoelectric) multiferroic materials. There are now several demonstrated strategies to achieve this goal, but retaining magnetic order above room temperature remains a difficult target. Iron oxides in the +3 oxidation state have high magnetic ordering temperatures due to the size of the coupled moments. Here we prepare and characterize ScFeO3 (SFO), which under pressure and in strain-stabilized thin films adopts a polar variant of the corundum structure, one of the archetypal binary oxide structures. Polar corundum ScFeO3 has a weak ferromagnetic ground state below 356 K-this is in contrast to the purely antiferromagnetic ground state adopted by the well-studied ferroelectric BiFeO3.

An 8-layer B-site deficient twinned hexagonal perovskite Ba8Ga4–xTa4+0.6xO24 has been synthesized and its structure and microwave dielectric properties characterized. This hexagonal perovskite consists of eight close-packed BaO3 layers stacked by a sequence of (ccch)2, where c and h refer to cubic and hexagonal BaO3 layers, respectively. The Ba8Ga4–xTa4+0.6xO24 ceramic materials exhibit composition-independent dielectric permittivity er ≈ 29, improved Qf value with the B-site vacancy content increase, and tunable temperature coefficient of resonant frequency τf from negative to positive. An optimum microwave dielectric performance was achieved for Ba8Ga0.8Ta5.92O24: Qf ≈ 29 000 GHz and τf ≈ 11 ppm/°C. The factors controlling the microwave dielectric properties are discussed in comparison with 8-layer twinned analogues and related 10-layer twinned hexagonal perovskites based on their structural and property data.

The auto-reduction of copper and manganese acetates has been investigated using in situ X-ray diffraction and thermogravimetric analysis, with the intention of manipulating the phenomena to tailor specific phase formation for synthesising catalysts. Subsequently catalysts prepared in this controlled manner were evaluated for ambient temperature CO oxidation. The decomposition of mixed copper and manganese acetate systems was controlled to form MnO x-supported Cu or CuMnOx spinel structures, depending on the oxygen concentration and flow conditions during the heat treatment. Catalyst precursors were prepared by physical grinding and by a supercritical CO 2 anti-solvent precipitation process. The use of supercritical anti-solvent precipitation allows for the formation of well-mixed metal acetates that decompose to form active spinel CO-oxidation catalysts or small copper nano-particles supported on MnOx, depending on the oxygen content of the heat treatment atmosphere. The ability to tune oxidation state and phase composition of catalysts is a key preparation parameter for controlling the activity and provides insight into the active sites for CO oxidation. © 2011 Elsevier Inc. All rights reserved.

BACKGROUND: This research investigated the effect of platinum (Pt) on the reactivity of tungsten oxide (WO3) for the visible light photocatalytic oxidation of dyes. RESULTS: Nanocrystalline tungsten oxide (WO3) photocatalysts were synthesised by a sol-gel process and employed for the photocatalytic degradation of Methyl Orange under visible light. For comparison commercial bulk WO3 materials were also studied for the same reaction. These materials were fully characterised using X-ray diffraction (XRD), UV-visible diffuse reflection spectroscopy and transmission electron microscopy (TEM). The photocatalytic oxidation of iso-propanol was used as a model reaction to follow the concomitant reduction of molecular oxygen. No reactions occured in the absence of platinum, which is an essential co-catalyst for the multi-electron reduction of oxygen. The platinised WO3 catalysts were stable for multiple oxidation–reduction cycles. The results from the catalytic activity measurements showed that platinised nanocrystalline WO3 is a superior oxidation photocatalyst when compared with bulk WO3. Methyl Orange was completely decolourised in 4 h. CONCLUSIONS: The enhanced performance of nanocrystalline Pt-WO3 is attributed to improved charge separation in the nanosized photocatalyst. Platinum is an essential co-catalyst to reduce oxygen. This photocatalyst could be applied to the treatment of organic pollutants in wastewater, with the advantage of using visible light compared with the widely studied TiO2, which requires UV light. Copyright © 2011 Society of Chemical Industry

The (AO)(ABO3)n Ruddlesden-Popper structure is an archetypal complex oxide consisting of two distinct structural units, an (AO) rock salt layer separating an n-octahedra thick perovskite block. Conventional high-temperature oxide synthesis methods cannot access members with n > 3, but low-temperature layer-by-layer thin film methods allow the preparation of materials with thicker perovskite blocks, exploiting high surface mobility and lattice matching with the substrate. This paper describes the growth of an n = 6 member CaO[(CSMO)2(LCMO)2 (CSMO)2] in which the six unit cell perovskite block is sub-divided into two central La0.67Ca0.33MnO3 (LCMO) and two terminal Ca0.85Sm0.15MnO3 (CSMO) layers to allow stabilization of the rock salt layer and variation of the transition metal charge.

Ba1.6Ca2.3Y1.1Fe5O13 is an Fe3+ oxide adopting a complex perovskite superstructure, which is an ordered intergrowth between the Ca2Fe2O5 and YBa2Fe3O8 structures featuring octahedral, square pyramidal, and tetrahedral B sites and three distinct A site environments. The distribution of A site cations was evaluated by combined neutron and X-ray powder diffraction. Consistent with the Fe3+ charge state, the material is an antiferromagnetic insulator with a Neel temperature of 480−485 °C and has a relatively low d.c. conductivity of 2.06 S cm−1 at 700 °C. The observed area specific resistance in symmetrical cell cathodes with the samarium-doped ceria electrolyte is 0.87 Ω cm2 at 700 °C, consistent with the square pyramidal Fe3+ layer favoring oxide ion formation and mobility in the oxygen reduction reaction. Density functional theory calculations reveal factors favoring the observed cation ordering and its influence on the electronic structure, in particular the frontier occupied and unoccupied electronic states.

Charge transfer between metal ions occupying distinct crystallographic sublattices in an ordered material is a strategy to confer visible light absorption on complex oxides to generate potentially catalytically active electron and hole charge carriers. CaCu3Ti4O12 has distinct octahedral Ti4+ and square planar Cu2+ sites and is thus a candidate material for this approach. The sol−gel synthesis of high surface area CaCu3Ti4O12 and investigation of its optical absorption and photocatalytic reactivity with model pollutants are reported. Two gaps of 2.21 and 1.39 eV are observed in the visible region. These absorptions are explained by LSDA+U electronic structure calculations, including electron correlation on the Cu sites, as arising from transitions from a Cu-hybridized O 2p-derived valence band to localized empty states on Cu (attributed to the isolation of CuO4 units within the structure of CaCu3Ti4O12) and to a Ti-based conduction band. The resulting charge carriers produce selective visible light photodegradation of 4-chlorophenol (monitored by mass spectrometry) by Pt-loaded CaCu3Ti4O12 which is attributed to the chemical nature of the photogenerated charge carriers and has a quantum yield comparable with commercial visible light photocatalysts.

Amino acid-functionalized Ni 4 (OH) 3 Cl tetrahedral clusters containing peptide linkages are linked into hexagonal planes connected pairwise into layers by neutral linkers. These layers stack to afford an open-framework structure, with large cavities occupied by non-ice-geometry (H 2 O) 16 clusters. The layer stacking motif and the guest cluster geometry are both determined by an intricate hierarchy of hydrogen-bonding interactions defined by the array of peptides supported by the tetrahedral units. The (H 2 O) 16 cluster adopts a non-ice-like structure due to the resulting highly symmetrical arrangement ofthe amide groups around the water molecules and the participation of two hydroxide anions per cluster.

A complex layered oxide has been synthesised as bulk material starting from the theoretical n = 2 R-P formula Sr 3 (Mg x Mo 1 − x ) 2 O 7 − δ ( x ≈ 0.25). This compound exhibits an unexpected crystal chemistry illustrated by the coexistence of several stacking modes — principally the ordered double perovskite Sr 2 MgMoO 6 − δ and n = 2 R-P type phase — inside the same crystallite. Chemical EDS analyses performed by TEM techniques have lead to an average chemical formula Sr 2.68 Mg 0.64 Mo 1.67 , which differs from the expected n = 2 R-P formula Sr 3 Mg 0.5 Mo 1.5 O 7 − δ in particular through a significant Sr deficiency. From high resolution electron microscopy (HREM) and Z-contrast (SuperSTEM) images, this analytical result is interpreted by the formation of a complex intergrowth [(Sr,Mg) 3 Mo 2 O 7 ] 1 − x [Sr 2 MgMoO 6 ] x with x ≈ 0.4. The resulting structure can be interpreted as a compositional segregation between Mg 2+ and Mo 6+ species in two basic structures, namely Sr 3 Mo 2 O 7 and Sr 2 MgMoO 6 .

A new mixed-ligand three-dimensional metal−organic framework is reported, where one component, meso-iminodisuccinic acid, is formed in-situ by the dimerization of aspartic acid under solvothermal conditions. The presence of a rigid pillaring co-ligand renders the framework truly porous and robust to guest loss.

The crystal structure of a solid controls the interactions between the electronically active units and thus its electronic properties. In the high-temperature superconducting copper oxides, only one spatial arrangement of the electronically active Cu(2+) units-a two-dimensional square lattice-is available to study the competition between the cooperative electronic states of magnetic order and superconductivity. Crystals of the spherical molecular C(60)(3-) anion support both superconductivity and magnetism but can consist of fundamentally distinct three-dimensional arrangements of the anions. Superconductivity in the A(3)C(60) (A = alkali metal) fullerides has been exclusively associated with face-centred cubic (f.c.c.) packing of C(60)(3-) (refs 2, 3), but recently the most expanded (and thus having the highest superconducting transition temperature, T(c); ref. 4) composition Cs(3)C(60) has been isolated as a body-centred cubic (b.c.c.) packing, which supports both superconductivity and magnetic order. Here we isolate the f.c.c. polymorph of Cs(3)C(60) to show how the spatial arrangement of the electronically active units controls the competing superconducting and magnetic electronic ground states. Unlike all the other f.c.c. A(3)C(60) fullerides, f.c.c. Cs(3)C(60) is not a superconductor but a magnetic insulator at ambient pressure, and becomes superconducting under pressure. The magnetic ordering occurs at an order of magnitude lower temperature in the geometrically frustrated f.c.c. polymorph (Néel temperature T(N) = 2.2 K) than in the b.c.c.-based packing (T(N) = 46 K). The different lattice packings of C(60)(3-) change T(c) from 38 K in b.c.c. Cs(3)C(60) to 35 K in f.c.c. Cs(3)C(60) (the highest found in the f.c.c. A(3)C(60) family). The existence of two superconducting packings of the same electronically active unit reveals that T(c) scales universally in a structure-independent dome-like relationship with proximity to the Mott metal-insulator transition, which is governed by the role of electron correlations characteristic of high-temperature superconducting materials other than fullerides.

The carboxylate ligand 1,3,6,8-tetrakis(p-benzoic acid)pyrene (TBAPy)-based on the strongly fluorescent long-lifetime pyrene core-affords a permanently microporous fluorescent metal-organic framework, [In(2)(OH)(2)(TBAPy)].(guests) (1), displaying 54% total accessible volume and excellent thermal stability. Fluorescence studies reveal that both 1 and TBAPy display strong emission bands at 471 and 529 nm, respectively, upon excitation at 390 nm, with framework coordination of the TBAPy ligands significantly increasing the emission lifetime from 0.089 to 0.110 ms. Upon desolvation, the emission band for the framework is shifted to lower energy: however, upon re-exposure to DMF the as-made material is regenerated with reversible fluorescence behavior. Together with the lifetime, the emission intensity is strongly enhanced by spatial separation of the optically active ligand molecules within the MOF structure and is found to be dependent on the amount and chemical nature of the guest species in the pores. The quantum yield of the material is found to be 6.7% and, coupled with the fluorescence lifetime on the millisecond time scale, begins to approach the values observed for Eu(III)-cryptate-derived commercial sensors.

Solid oxide fuel cells (SOFCs) are a major candidate technology for clean energy conversion because of their high efficiency and fuel flexibility.1 The development of intermediate-temperature (500–750 °C) SOFCs requires electrolytes with high oxide ion conductivity (exceeding 10−2 S cm−1 assuming an electrolyte thickness of 15 μm1). This conductivity, in turn, necessitates enhanced understanding of the mechanisms of oxide ion charge carrier creation and mobility at an atomic level. The charge carriers are most commonly oxygen vacancies in fluorites2, 3 and perovskites.3, 4 There are fewer examples of interstitial-oxygen-based conductors such as the apatites5, 6 and La2Mo2O9-based materials,7–9 so information on how these excess anion defects are accommodated and the factors controlling their mobility is important.

This paper reports the evaluation of the cubic B site cation-ordered double perovskite system Ba2Co2−x(Mo1/2Nb1/2)xO6, resulting in the single phase composition Ba2CoMo0.5Nb0.5O6−δ (BCMN) with a mixed Co charge state stabilized by a combination of Mo and Nb doping as a new mixed conductor with potential SOFC cathode applications. X-ray, neutron, and electron diffraction show that hexagonal intergrowths found in multiple phase samples at lower Mo/Nb contents are suppressed in BCMN, which has large domains of rock-salt ordered B site cations with separate Co and Mo/Nb sites. Conductivity measurement and impedance spectroscopy investigation shows that BCMN has a considerably reduced dc conductivity compared with materials such as BSCF but exhibits comparable electrochemical properties to some existing cathode materials in symmetrical cell measurements, and shows higher structural stability and reduced reactivity with the Ce0.8Sm0.2O2−δ (SDC) electrolyte. The role of Mo in dioxygen activation is proposed to o...

Supercritical CO2 is used as an antisolvent to precipitate out nanostructured homogeneous mixtures of Cu2+ and Mn3+ with crystallites of 10–20 nm in diameter. Following calcination, this material forms a crystalline tetragonal spinel, CuMn2O4, with a branched chainlike structure with a length of 160–200nm and diameters of approximately 40nm. This new material is more than twice as active per unit surface area as the conventionally prepared hopcalite catalysts for the oxidation of carbon monoxide. This is the first time that homogeneous mixed oxides have been formed using this method.

The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 A(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.

The thermal evolution of the crystal structure of PrSr3Co1.5Fe1.5O10–d , a member of the n = 3 family of Ruddlesden-Popper compounds, has been studied by means of variable temperature synchrotron X-ray powder diffraction combined with room temperature neutron diffraction studies. This structure takes the ideal tetragonal I4/mmm (n°139) space group. The possibility of symmetry lowering to the Pbca (n°61) space group by slight tilting and rotation of the oxygen atoms around the octahedral B site is discussed. The non linear thermal expansion of the compound in air is caused by a chemical expansion accompanying the loss of oxygen that comes in addition to normal thermal expansion. A mechanism describing the creation of oxygen vacancies is proposed.

Metal lite: High-resolution neutron powder diffraction data reveals that the body-centered cubic crystal structure of lithium(0)tetraamine transforms to a simple cubic structure below 22 K. The detailed structure determinations will allow new insights into the coupled structural and electronic properties of the lightest metal.

The manufacture of heterogeneous catalysts and catalyst supports produces substantial amounts of nitrate containing aqueous effluent. The use of nitrate free precursors and an environmentally friendly process would change the manufacture so that the entire process of catalyst synthesis and use can be considered green. In this work the precipitation of titania acetylacetonate nanoparticles for use as catalytic supports using a supercritical carbon dioxide anti-solvent process was investigated over a range of conditions. The effects of 1) pressure, 2) temperature, 3) solution flowrate, 4) solution concentration of TiO(acac) 2 in methanol, 5) nozzle diameter and 6) CO 2 /methanol flow ratio on the mean particle size and morphology were studied. Particle sizes between 27 and 78 nm were obtained and were generally string and branch-like with an amorphous nature. Pressure and temperature had little effect on the mean particle size. A decrease in the velocity of the solution flow rate led to an increase in mean particle size and to particles that exhibited greater interconnectivity. It was also observed that an increase in concentration of TiO(acac) 2 in methanol led to an increase in mean particle size. The process shows promise for the production of catalysts by an environmentally acceptable route.

A method for the in situ preparation of Pt nanoparticles of controlled size based on the modification of highly oriented pyrolytic graphite (HOPG) with aminophenyl groups employing diazonium chemistry is demonstrated. It is shown that full chemical reduction of an Ar–NO2 grafted surface is achieved with aqueous Sn(II). The formation of aminophenyl groups was established by chemical reaction with 1,2-benzoquinone followed by electrochemical detection of the bound quinone using square wave voltammetry. The oxidation state of nitrogen was confirmed by XPS. Platinum nanoparticles were prepared chemically by the attachment of Pt(II) on the Ar–NH2 modified electrodes followed by reduction with NaBH4. This resulted in the formation of Pt nuclei that could be further grown. The surfaces formed were characterized by TEM, XRD and XPS. The dependence on particle size of the electro-oxidation of CO and methanol in 0.5 M H2SO4 was studied for three different nanoparticle sizes, 2.0, 2.7 and 4.0 nm. It is demonstrated that reactivity for these reactions decreases with decreasing particle size. The difficulties in comparing particle sizes calculated from XRD data with those from TEM are discussed.

A2B2O7 complex oxides with the pyrochlore structure feature a wide variety of chemical compositions and corresponding diverse electrical and physical properties. A new pyrochlore, Yb0.96Ca1.04TiNbO6.98, is reported and characterized in terms of structural stability and electrical properties. The material is stable to ∼1450 °C in 5% H2/N2 and has a high electronic conductivity in a reducing atmosphere, e.g., 9 S/cm at 800 °C in 5% H2/N2 after high-temperature reduction. Other cation substitutions enhance the low-temperature kinetics of conductivity response to changes in oxygen partial pressure.

A new six-layer perovskite-related structure Ba 6Na 2Nb 2M 2O 17 (M = P, V), which consists of cubic (c) BaO 3 layers and oxygen-deficient pseudocubic (c') BaO 2 layers stacked in the sequence c'ccccc, is presented. In Ba 6Na 2Nb 2M 2O 17, two-dimensional slabs of the well-known 2:1 octahedral cation-ordered perovskite motif are isolated between layers of tetrahedral units formed by anion vacancy ordering: two consecutive NbO 6 octahedral layers are sandwiched by two single NaO 6 octahedral layers, which, in turn, connect with two isolated MO 4 tetrahedral layers. Both oxides are derived from the 2:1 ordered perovskite structure (e.g., Ba 3ZnTa 2O 9) by ordered removal of O atoms in every sixth BaO 3 layer. Both materials exhibit a relative permittivity of approximately 20-23, Q x f 0 values of approximately 7800-10600 GHz, and negative temperature coefficients of the resonant frequency of approximately -23 to -7 ppm/ degrees C.

Reaction of L-cysteine with M(NO3)2 x xH2O (M = Cd, Zn) generates M(L-cysteinate), which feature one-dimensional substructures that can be viewed as fragments of bulk structures of CdS (rock salt high pressure phase) and ZnS (wurtzite) because of the bridging modes accessible to the sulfur atom of L-cysteine. The MS substructures are arranged in a regular and periodic fashion within the crystal via the carboxylate function of L-cysteine. Considering the structural similarities with bulk materials, the optical properties of M(L-cysteinate) were studied and indicate blue shifts of the band gap of 2.59 eV (M = Cd, compared to CdS rock salt) and 1.37 eV (M = Zn, compared to ZnS wurtzite) with respect to the bulk MS structures, due to the low dimensionality of the metal-sulfur arrangement. The chelating nature of the cysteine ligand imposes an unusual mer arrangement of three binding S moieties at Cd with a correspondingly high Cd coordination number in a chalcogenide-based material. Density of states calculations show strong electronic structure similarities with the bulk phases and rationalize the band gap changes.

The hyperexpanded (CH3NH2)K3C60 fulleride and its perdeuterated analogue were investigated by 1H and 2H NMR spectroscopy between room temperature and 4 K. Two phase transitions at TS = 220 K and TN = 11 K clearly were detected in the temperature dependence of the NMR line shapes, the spectral first (M1) and second (M2) moments, and the spin lattice relaxation times, T1. From 2H NMR line shape analysis, we found that the structural phase transition at TS was driven by the freezing out of the discrete Markovian-type jump motion of the entire K+-ND2CD3 unit that is characterized by an activation energy, Ea = 236(51) meV. Below TS, a sudden change in the temperature dependence of M1 suggests the appearance of a small but nonzero spin density on the K+-NH2CH3 unit. This could influence the electronic properties of the fulleride phase by modulating the strength of the exchange interactions between C603− anions and controlling the width, W, of the t1u-derived band. The 1H NMR spectra below TN show significant li...

Methane storage is important for the development of alternative energy carriers. The synthesis and methane storage properties of microporous hypercrosslinked organic polymers are reported. The figure shows a simulation of methane sorption in microporous hypercrosslinked poly(p-dichloroxylene); up to 5.2 mmol g(-1]) CH4 at 20 bar/298 K; isosteric heat of sorption similar to 21 kJ mol(-1).

Substitution of the pillaring ligand in the homochiral open-framework [Ni(2)(L-asp)(2)(bipy)] by extended bipy-type ligands leads to a family of layer-structured, homochiral metal-organic frameworks. The 1D channel topology can be modified by the nature of the organic linker, with shape, cross-section and the chemical functionality tuneable. In addition, the volume of these channels can be increased by up to 36 % compared to the parent [Ni(2)(L-asp)(2)(bipy)]. The linker 1,4-dipyridylbenzene (3rbp) gives access to a new layered homochiral framework [Ni(2)(L-asp)(2)(3rbp)] with channels of a different shape. In specific cases, non-porous analogues with the linker also present as a guest can be activated to give porous materials after sublimation. Their CO(2) uptake shows an increase of up to 30 % with respect to the parent [Ni(2)(L-asp)(2)(bipy)] framework.

High-conductivity oxide ion electrolytes are needed to reduce the operating temperature of solid-oxide fuel cells. Oxide mobility in solids is associated with defects. Although anion vacancies are the charge carriers in most cases, excess (interstitial) oxide anions give high conductivities in isolated polyhedral anion structures such as the apatites. The development of new families of interstitial oxide conductors with less restrictive structural constraints requires an understanding of the mechanisms enabling both incorporation and mobility of the excess oxide. Here, we show how the two-dimensionally connected tetrahedral gallium oxide network in the melilite structure La1.54Sr0.46Ga3O7.27 stabilizes oxygen interstitials by local relaxation around them, affording an oxide ion conductivity of 0.02–0.1 S cm−1 over the 600–900 ∘C temperature range. Polyhedral frameworks with central elements exhibiting variable coordination number can have the flexibility needed to accommodate mobile interstitial oxide ions if non-bridging oxides are present to favour cooperative network distortions. Fast-ion conductors are needed to reduce the operating temperature of solid-oxide fuel cells. The identification of the conduction mechanism in electrolytes where conduction is based on mobile oxygen interstitials rather than the usual anion vacancies offers a generic design principle for novel solid electrolytes.

C(60)-based solids are archetypal molecular superconductors with transition temperatures (Tc) as high as 33 K (refs 2-4). Tc of face-centred-cubic (f.c.c.) A(3)C(60) (A=alkali metal) increases monotonically with inter C(60) separation, which is controlled by the A(+) cation size. As Cs(+) is the largest such ion, Cs(3)C(60) is a key material in this family. Previous studies revealing trace superconductivity in Cs(x)C(60) materials have not identified the structure or composition of the superconducting phase owing to extremely small shielding fractions and low crystallinity. Here, we show that superconducting Cs(3)C(60) can be reproducibly isolated by solvent-controlled synthesis and has the highest Tc of any molecular material at 38 K. In contrast to other A(3)C(60) materials, two distinct cubic Cs(3)C(60) structures are accessible. Although f.c.c. Cs(3)C(60) can be synthesized, the superconducting phase has the A15 structure based uniquely among fullerides on body-centred-cubic packing. Application of hydrostatic pressure controllably tunes A15 Cs(3)C(60) from insulating at ambient pressure to superconducting without crystal structure change and reveals a broad maximum in Tc at approximately 7 kbar. We attribute the observed Tc maximum as a function of inter C(60)separation--unprecedented in fullerides but reminiscent of the atom-based cuprate superconductors--to the role of strong electronic correlations near the metal-insulator transition onset.

Well-characterized bulk materials in the candidate dilute magnetic semiconductor system In 2-x Cr x O 3 are prepared for 0

The introduction of mixed valency into extended main-group solids is discussed using the example of hole-doped LiBC, where a combination of experimental measurements and density functional theory calculations is used to understand the observed electronic properties in terms of deviation from the expected rigid-band electronic structure behaviour.

In situ synchrotron X-ray powder diffraction is used to study the kinetics of cation ordering and ordered domain growth in the microwave dielectric electroceramic Ba3ZnTa2O9 (BZT) with a time resolution of 15 s and processing temperatures of up to 1500 °C. This permits the measurement of the activation energy for cation ordering and the identification of different mechanisms for ordered domain growth, associated with the formation of the Ba8ZnTa6O24 impurity phase due to zinc loss.

The electron paramagnetic resonance (EPR) technique is used to study the temperature evolution of the electronic and magnetic properties of the hyperexpanded fulleride (CH 3 NH 2 )K 3 C 60 in the temperature range 4-294 K. Unambiguous signatures for the development of large internal magnetic fields and a transition to an antiferromagnetic ground state below T N = 11 K are provided by the temperature dependence of the spin susceptibility, the EPR line width, and the position of the EPR line. The EPR results in the paramagnetic regime are indicative of an insulating electronic state, with localized S = 1/2 moments on the C 60 3- ions. The accompanying complex evolution of the spin susceptibility, EPR line width, and g-factor anisotropy furthermore reveals that effects of electronic origin (t 1u orbital order-disorder transition, crossover from static to dynamic Jahn-Teller distortions) in the vicinity of the structural transformation are important for the understanding of the exchange interactions between the fulleride ions.

A 21R-type mixed conducting oxygen-deficient hexagonal perovskite Ba7Y2Mn3Ti2O20 was synthesized and its structure characterized by variable temperature neutron powder diffraction. The structure is characterized by the presence of both BaO2 and BaO3 layers. In the oxygen-stoichiometric material, the vacancies are ordered in c‘-BaO2 layers. Extra oxygen is accommodated by intergrowth of the vacancy-ordered c‘-BaO2 layers with cubic c-BaO3-x layers (x ≅ 1), which have disordered 2/3 oxygen occupancy. This material displays mixed electronic and oxide ionic conduction at high temperature, and the role of the two distinct and partially occupied anion sites within the BaO2 layers in permitting the oxygen mobility is discussed.

A series of hypercrosslinked polymer networks has been synthesized by the self-condensation of bischloromethyl monomers such as dichloroxylene (DCX), 4,4‘-bis(chloromethyl)-1,1‘-biphenyl (BCMBP), and 9,10-bis(chloromethyl)anthracene (BCMA). These materials are predominantly microporous and exhibit Brunauer−Emmett−Teller (BET) surface areas of up to 1904 m2/g as measured by N2 adsorption at 77.3 K (Langmuir surface area = 2992 m2/g). Networks based on BCMBP exhibit a gravimetric storage capacity of 3.68 wt % at 15 bar and 77.3 K, the highest yet reported for an organic polymer. The micro- and mesostructure of the networks is explained by a combination of solid-state NMR, gas sorption measurements, pycnometry, and molecular simulations. The isosteric heat of sorption for H2 on these materials is found to be in the range 6−7.5 kJ/mol. A molecular model is presented for a p-DCX network that simulates well certain key physical properties such as pore volume, pore width, absolute density, and bulk density. This...

The cation ordering in the fluorite-like transparent conductors In{sub 4+} {sub x} Sn{sub 3-2} {sub x} Sb {sub x} O{sub 12} and In{sub 6}TeO{sub 12}, was investigated by Time of Flight Neutron Powder Diffraction and X-ray Powder Diffraction (tellurate). The structural results including atomic positions, cation distributions, metal-oxygen distances and metal-oxygen-metal angles point to a progressive cation ordering on both sites of the Tb{sub 7}O{sub 12}-type structure with a strong preference of the smaller 4d {sup 10} cations (Sn{sup 4+}, Sb{sup 5+}, Te{sup 6+}) for the octahedral sites. The corresponding increase of the overall structure-bonding anisotropy is analyzed in terms of the crystal chemical properties of the OM {sub 4} tetrahedral network of the antistructure. The relationships between the M {sub 7}O{sub 12} and the M {sub 2}O{sub 3} bixbyite-type structures are explored. Within the whole series of compositions In{sub 4+} {sub x}M {sub 3-} {sub x} O{sub 12} (M=Sn, Sb, Te) there exists an increase of the symmetry gap between the more symmetrical bixbyite structure and the M {sub 7}O{sub 12} type. This is tentatively correlated with the progressive weakening of thermal stability of these compositions from Sn to Te via Sb. - Graphical abstract: Hexagonal cell of themore » fluorite-like oxygen-deficient M {sub 7}O{sub 12} structure: symmetrical octahedra and distorted sevenfold-coordinated polyhedra are shown.« less

We report a synthetic material, [Co 2 (bipy) 3 (SO 4 ) 2 (H 2 O) 2 ](bipy) (CH 3 OH), ( 1 , where bipy = 4,4′-bipyridyl) that contains discrete reactive and inert structural motifs that undergo a reversible substitution reaction involving the concerted and spatially controlled introduction of bipyridine and methanol molecules at the reactive sites. This reaction defines the pore geometry of the resulting open-framework structure and controls the manner in which this structure sorbs small molecules. The molecules involved in the reaction are positioned by an array of well-defined interactions during their path to binding to the metal centers.

The potential solid oxide fuel cell anode material Sr2MgMoO6 adopts a √2 × √2 × 2 I1 superstructure of the simple perovskite cell, derived from an a0a0c- tilt system via distortion of the Mg- and Mo-centered octahedra. Reduction of Sr2MgMoO6 appears to be correlated with antisite disorder at either point or extended antiphase defects. The degree of reduction is small at temperatures below 900 °C. Upon further reduction above 900 °C, Sr2MgMoO6 begins to decompose into a reduced material modeled as an n = 2 Ruddlesden−Popper phase with a significantly higher Mo:Mg ratio, MgO, and Mo. Diffraction data are consistent with the reduced material being significantly intergrown with the perovskite matrix.

Copper and zinc form an important group of hydroxycarbonate minerals that include zincian malachite, aurichalcite, rosasite and the exceptionally rare and unstable—and hence little known and largely ignored1—georgeite. The first three of these minerals are widely used as catalyst precursors2, 3, 4 for the industrially important methanol-synthesis and low-temperature water–gas shift (LTS) reactions5, 6, 7, with the choice of precursor phase strongly influencing the activity of the final catalyst. The preferred phase2, 3, 8, 9, 10 is usually zincian malachite. This is prepared by a co-precipitation method that involves the transient formation of georgeite11; with few exceptions12 it uses sodium carbonate as the carbonate source, but this also introduces sodium ions—a potential catalyst poison. Here we show that supercritical antisolvent (SAS) precipitation using carbon dioxide (refs 13, 14), a process that exploits the high diffusion rates and solvation power of supercritical carbon dioxide to rapidly expand and supersaturate solutions, can be used to prepare copper/zinc hydroxycarbonate precursors with low sodium content. These include stable georgeite, which we find to be a precursor to highly active methanol-synthesis and superior LTS catalysts. Our findings highlight the value of advanced synthesis methods in accessing unusual mineral phases, and show that there is room for exploring improvements to established industrial catalysts.

A superconductivity dome is created by the electronic structure of the molecular building block of an unconventional superconductor., Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above Tc is a major challenge for all unconventional superconductors. The molecular A3C60 fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C603– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of Tc with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

Reaction of iron(IIII)chloride with the free base tetrakis(4-carboxyphenyl)porphyrin (H2TCPP) in the presence of different bases leads to the formation of a series of iron/porphyrin metal–organic frameworks. Such a crystal engineering approach led to the obtaining of four structures presenting three different topologies and inorganic secondary building units. Depending on the synthesis conditions, isolated FeIII octahedra, diiron(II) paddle wheel dimers, or extended [FeIII(OH)O4]n chains could be obtained in a controlled manner. The influence of the synthetic conditions on the final structure and the oxidation state of iron is discussed. Stability of the porous solids towards air and water is studied, and their intrinsic porosity is assessed.

Ferroelectric and ferromagnetic materials exhibit long-range order of atomic-scale electric or magnetic dipoles that can be switched by applying an appropriate electric or magnetic field, respectively. Both switching phenomena form the basis of non-volatile random access memory1, but in the ferroelectric case, this involves destructive electrical reading and in the magnetic case, a high writing energy is required2. In principle, low-power and high-density information storage that combines fast electrical writing and magnetic reading can be realized with magnetoelectric multiferroic materials3. These materials not only simultaneously display ferroelectricity and ferromagnetism, but also enable magnetic moments to be induced by an external electric field, or electric polarization by a magnetic field4,5. However, synthesizing bulk materials with both long-range orders at room temperature in a single crystalline structure is challenging because conventional ferroelectricity requires closed-shell d0 or s2 cations, whereas ferromagnetic order requires open-shell dn configurations with unpaired electrons6. These opposing requirements pose considerable difficulties for atomic-scale design strategies such as magnetic ion substitution into ferroelectrics7,8. One material that exhibits both ferroelectric and magnetic order is BiFeO3, but its cycloidal magnetic structure9 precludes bulk magnetization and linear magnetoelectric coupling10. A solid solution of a ferroelectric and a spin-glass perovskite combines switchable polarization11 with glassy magnetization, although it lacks long-range magnetic order12. Crystal engineering of a layered perovskite has recently resulted in room-temperature polar ferromagnets13, but the electrical polarization has not been switchable. Here we combine ferroelectricity and ferromagnetism at room temperature in a bulk perovskite oxide, by constructing a percolating network of magnetic ions with strong superexchange interactions within a structural scaffold exhibiting polar lattice symmetries at a morphotropic phase boundary14 (the compositional boundary between two polar phases with different polarization directions, exemplified by the PbZrO3–PbTiO3 system) that both enhances polarization switching and permits canting of the ordered magnetic moments. We expect this strategy to allow the generation of a range of tunable multiferroic materials.