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A stable visible-light driven photocatalyst (λ ≥ 450 nm) for H2O oxidation is prepared by Rh substitution into the pyrochlore Y2Ti2O7 to a maximum level of 2% by stoichiometric solid state reactions of Y2O3, TiO2, and Rh2O3 under air (Pt foil lined alumina boat, 1300 °C, 2 d).

The title compound is prepared by solid state reaction of stoichiometric mixtures of BaCO3, Ga2O3, and In2O3 (alumina boat, 12 h at either 1100, 1200, or 1300 °C under ambient air) and characterized by powder XRD, time-of-flight neutron diffraction, and impedance measurements.

A method for the computational identification of materials containing multiple atom types in multiple geometries by ranking candidate structures assembled from extended modules containing chemically realistic atomic environments is presented.

BaFe9LiO15 is prepared by solid state reaction of a stoichiometric mixture of BaCO3, Fe2O3, and Li2CO3 (1.

The new title compound is prepared by solid state reaction of stoichiometric mixtures of CaCO3, Ga2O3, and Nb2O3 (1225 °C, 60 h) and characterized by X-ray and neutron diffraction.

The title perovskite (0 ≤ x ≤ 3.6) is synthesized from stoichiometric amounts of BaCO3, Ga2O3, and Ta2O5 (1200 °C for 12 h and 1450 °C for 24 h).

Ba1.6Ca2.3Y1.1Fe5O13 is an FeIII oxide with a complex perovskite superstructure, which is an intergrowth between the Ca2Fe2O5 and YBa2Fe3O8 structures featuring octahedral, square pyramidal, and tetrahedral B sites and three distinct A site environments.

Cristallisation dans I4/mmm avec a T=5K: a=4.29650, c=13.2285A et a T=298K: a=4.30241, c=13.26070A; affinement jusqu'a R w p=2.6 a T=5K et R w p=5.1 a T=298K. Anterieur on a surestime la distorsion tetragonale.

Alkali metal fullerides (A x C 60 ) are a subject of considerable current interest because of the occurrence of superconductivity for A x C 60 at temperatures surpassed only by the high T c copper oxides. The preparation and characterization of A x C 60 (A = alkali metal, x = 2,3,4,6) by powder X-ray diffraction, NMR ( 13 C, 23 Na and 87 Rb), and d.c. magnetization are reported. The structures are described as intercalation compounds of the FCC structure of pristine c 60 or of hypothetical BCC or BCT structures. The structures and phase diagrams can be rationalized on the basis of ion size and electrostatic considerations. Only the A 3 C 60 compounds are metallic (and superconducting). The superconducting T c increases nearly linearly with unit cell size. EHT (Extended Huckel Theory) calculations and 13 C NMR relaxation measurements indicate higher densities of states for the higher T c compositions.

Incorporation of elemental phosphorus into hexagonal-packed C60 gives the new phase {(P4)2C60}; characterisation by powder diffraction and multinuclear solid-state NMR studies show the P4 tetrahedra occupy trigonal prismatic sites and confirm the retention of the molecular nature of the P4 guest.

The first examples of post-transition metal intercalation into a fullerene host are mercury-loaded derivatives of Na2C60.

The preparation and crystal structures of the n = 2 Ruddlesden−Popper phases Sr2-xLn1+xMn2O7 (0 ≤ x ≤ 0.5, Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, and Er) are described. The crystal chemistry and stability of this structure is governed by the size of the lanthanide cation. Partial ordering of the Sr2+ and Ln3+ cations occurs between the two available A cation (A = Ln3+, Sr2+) sites, with the smaller lanthanides preferring the site in the rock-salt layer over that in the perovskite block. This ordering is almost complete for the small lanthanides (Tb−Er), and these ordered compounds can be prepared as single phases. Cation disorder in compounds of the larger lanthanides is accompanied by a subtle separation into two n = 2 Ruddlesden−Popper phases, which is apparent only upon detailed inspection of Rietveld refinements of the X-ray profiles. In these cases, the two-phase model is found to be superior to a single phase model with strain broadening included. For a particular lanthanide, both the ease of s...

The article is a summary of recent work on the synthesis of new types of metal fulleride designed to examine the influence of various chemical factors on the physical properties of this class of material. Fullende charge spacing, orientations are examined, together with the insertion of less electropositive cations on the interstitial sites.

Details of the synthesis and structural and physical characterization of oxides with the nominal composition NaTiO2 are presented. The highest sodium loading we have achieved is Na0.99(2)TiO2 determined using diffraction methods. The results are not consistent with a localized moment d1 system. High-resolution neutron diffraction shows that the transition observed previously between 200 and 250 K in the magnetic susceptibility has a structural, rather than purely magnetic, origin. At room temperature Na0.99(2)TiO2 has the α-NaFeO2 structure, space group R3m (No. 166), with the hexagonal lattice parameters a = 3.04537(1) A, c = 16.26210(4) A, and Z = 3. On cooling, a continuous, broad, nonhysteretic transition to a monoclinic phase occurs at about 250 K. Between 220 and 250 K, the two phases coexist, the precise temperature range of coexistence being correlated with the width of the Bragg reflections in different samples. At 5 K the monoclinic structure adopts the space group C2/m (No. 12) with a = 5.2455...

The crystal structures of Sr2HoMn2O7 and Sr2YMn2O7 have been determined at 290 and 1.7 K from neutron and X-ray powder diffraction data. Both are distorted Ruddlesden−Popper structures formed by the intergrowth of rock-salt-like layers and perovskite-like blocks of tilted MnO6 octahedra (space group P42/mnm; for Ho at 290 K a = 5.40388(5), c = 19.9050(2) A). The majority of the lanthanide cations are located in the rock-salt layers. Neither structure changes significantly on cooling to 1.7 K. There is evidence for neither charge ordering of Mn3+ and Mn4+ cations nor for long-range magnetic ordering. The magnetic susceptibility maximum observed previously is thus confirmed as signifying a transition to a spin-glass phase. The behavior of these compounds is contrasted with that of other Mn oxides which show long-range magnetic order and colossal magnetoresistance.

Reaction of solids of pure D2d and D2 C84, as well as mixtures of these isomers, with an excess of potassium produces the cubic phases K8+xC84, with multiple occupancy of the octahedral site by potassium. Analysis of X-ray powder diffraction data reveals that the anions adopt well-defined orientations in the solid, driven by the anion−cation contacts. Electron paramagnetic resonance measurements on the solid fullerides indicate that the electronic properties depend on the particular isomer of C84 used as host.

The current status of metal intercalation into fullerene hosts is reviewed. The extent to which widely accepted simple models of the metallic and superconducting behavior in the A3C60 compounds are sustainable is examined. The search for higher superconducting transition temperatures is discussed in the context of the synthesis of fullerides with different anion charges, more complex structures, and derived from higher fullerene hosts.

The room-temperature crystal structures of the n = 3 Ruddlesden−Popper phases Ca4Mn2FeO9.75 and Sr4Mn2FeO9.80 have been refined from neutron and X-ray powder diffraction data. Both adopt space group I4/mmm with (a,c) = (Ca, 3.73683(1), 27.0860(1) A), (Sr, 3.83393(1), 27.8148(1) A). In both compounds the cation site at the center of the perovskite blocks is preferentially occupied by Fe (Ca, Mn:Fe = 0.424:0.576(4)), and the anion vacancies are found around this site. The occupied anion sites show static disorder in Ca4Mn2FeO9.75 but not in Sr4Mn2FeO9.80. Both compounds are electrical insulators which order antiferromagnetically at TN = 75 K (Ca) or 90 K (Sr). Susceptibility and M(H) data suggest that not all the Mn and Fe cations take part in the long-range magnetic ordering, and there is evidence of a spin glass transition in both compounds at ∼11 K. The magnetic structure of Ca4Mn2FeO9.75 at 5 K has been determined by neutron diffraction. No ordered moment was detected on the Mn/Fe site at the center of ...

The capability of sodium hydride as a reducing agent in oxide deintercalation reactions is explored. The Ni(III) perovskite LaNiO3 can be reduced topotactically to LaNiO2, isostructural with the “infinite layer” cuprates, using solid sodium hydride in a sealed evacuated tube at 190 ≤ T/°C ≤ 210, and a similar infinite-layer phase is prepared by reduction of NdNiO3. Structural characterization indicates the coexistence of incompletely reduced regions, with five-coordinate Ni centers due to the introduction of oxide anions between the NiO23- sheets, giving samples with a refined stoichiometry of LaNiO2.025(3). Neutron powder diffraction and magnetization measurements indicate that the lamellar Ni(I) phase does not show the long-range antiferromagnetic ordering characteristic of isoelectronic Cu(II) oxides. This may be due either to the influence of the interlamellar oxide defect regions or to the reduced covalent mixing of Ni 3d and O 2p levels.

A reducing and nitriding atmosphere has been used to control the composition and structure of zirconium titanium oxynitrides over a wide range. Magnetic susceptibility and electrical conductivity measurements are consistent with localization of the electrons, introduced into the conduction band on synthesis, by the Anderson mechanism.

The substitution of Ga3+ into the Jahn−Teller distorted, antiferromagnetic perovskites LaMnO3 and NdMnO3 strongly affects both the crystal structures and resulting magnetic ordering. In both compounds the Ga3+ and Mn3+ cations are disordered over the six coordinate sites. La2GaMnO6 is a ferromagnetic insulator (Tc = 70 K); a moment per Mn cation of 2.08(5) μB has been determined by neutron powder diffraction at 5 K. Bond length and displacement parameter data suggest Jahn−Teller distortions which are both coherent and incoherent with the Pnma space group symmetry of the perovskite structure (a = 5.51122(4) A, b = 7.80515(6) A, c = 5.52947(4) A) at room temperature. The coherent distortion is strongly suppressed in comparison with the parent LaMnO3 phase, but the displacement ellipsoids suggest that incoherent distortions are significant and arise from local Jahn−Teller distortions. The preparation of the new phase Nd2GaMnO6 has been found to depend on sample cooling rates, with detailed characterization n...

The synthesis and characterization of two members of a family of porous magnetic materials is described. The structures of Co4(SO4)(OH)6(C2N2H8)0.5*3H2O and Co4(SO4)(OH)6(C6N2H12)0.5*H2O and their thermal stability can be tailored via the choice of organic pillar. The interactions between the pillaring agent and the compositionally complex inorganic layer are discussed. The influences of two pillaring agents i.e., the flexible ethylenediamine and the relatively rigid 1,4-diazabicyclo[2,2,2]octane, on thermal stability, rigidity upon guest loss, and magnetic behavior of the pillared solids are compared. The magnetism of the pillared layered cobalt hydroxides is complex due to the influences of multiple metal sites, inter- and intralayer exchange, spin-orbit coupling, and geometrical frustration. The wide variety of potential pillars, oxyanions, and possible metal substitutions at the octahedral and tetrahedral sites offers the possibility of tailoring the magnetic and porous properties of these materials.

It is shown by magnetometry and μSR spectroscopy that short-range magnetic interactions between the Mn cations in the nonmetallic K2NiF4-like phase La0.8Sr1.2Mn0.6Rh0.4O4 become significant below ∼200 K. Negative magnetoresistance (ρ/ρ(0) ∼ 0.5 in 14 T at 108 K) is apparent below this temperature. Neutron diffraction has shown that an applied magnetic field of 5 T is sufficient to induce saturated (3.38(7)μB per Mn) long-range ferromagnetic ordering of the atomic moments at 2 K, and that the induced ordering persists up to a temperature of 50 K in 5 T. Spin glass behavior is observed below 20 K in the absence of an applied field. The induced magnetic ordering is attributed to the subtle changes in band structure brought about by the external field, and to the controlling influence of Rh3+ over the relative strength of competing magnetic exchange interactions.

Oxidation of the ferromagnetic B-site diluted manganese(III) perovskite La2GaMnO6 is investigated by synthesis of the La2-xSrxGaMnO6 series. At the x = 0.3 composition, which corresponds to diamagnetic element substitution at the B-site of metallic LaO.7SrO.3MnO3, the MnIII and MnIV valences order in real space at low temperature with an unusual lamellar motif. Orbital ordering at the MnIII centers in this array maintains ferromagnetism and enhances the static coherent Jahn-Teller distortion over that found for the pure MnIII end-member, facilitating eg electron hopping in the insulating state. Further oxidation to x = 0.5 completely suppresses the charge and orbital ordering, leading to glassy rather than long-range ordered magnetism.

Polycrystalline samples of La4LiMnO8 and La3SrLiMnO8 have been studied by a combination of X-ray diffraction (XRD), neutron diffraction (ND), 6Li MAS NMR, electron microscopy (EM), and magnetometry. Room-temperature XRD and ND measurements suggest that both compounds have the K2NiF4 structure, with a disordered arrangement of Li and Mn over the six-coordinate sites. However, MAS NMR and EM demonstrate the presence of local 1:1 Li:Mn order on these sites, and EM shows that although cation order is well-developed in each xy sheet of corner-sharing octahedra, the sheets are stacked randomly along z. The structures are best described as paracrystalline, and many of the concepts of conventional crystallography are inapplicable. Magnetometry and low-temperature ND experiments show that, despite their paracrystallinity, the two compounds are ordered antiferromagnetically with susceptibility maxima at 26 and 18 K, respectively, and with ordered magnetic moments of 3.61(6) and 2.3(1) μB per Mn cation at 2 K. Aniso...

We present the synthesis and structural characterization of a transition metal oxide hydride, LaSrCoO3H0.7, which adopts an unprecedented structure in which oxide chains are bridged by hydride anions to form a two-dimensional extended network. The metal centers are strongly coupled by their bonding with both oxide and hydride ligands to produce magnetic ordering at temperatures up to at least 350 kelvin. The synthetic route is sufficiently general to allow the prediction of a new class of transition metal–containing electronic and magnetic materials.

Ammonolysis of reactive oxide precursors affords the vanadium(V) phase Ba2VO3N that is shown by X-ray and neutron powder diffraction and Raman spectroscopy to contain pseudotetrahedral VO3N4- anions. This is the first example of such species for the first transition series metals.

The perovskite- and K2NiF4-structure group 5 oxynitrides SrTaO2N, BaTaO2N, Sr2TaO3N, and Ba2TaO3N, previously prepared by reacting oxide precursors with ammonia, may also be prepared by the reaction between the appropriate alkaline earth oxide and TaON at 1500 °C under 1 atm of pure nitrogen gas for a few hours. The nitrogen atmosphere is essential to prevent reduction of TaV, and the method of inductive heating ensures that the nitrogen atmosphere above the sample is maintained free of oxygen or water. SrTaO2N crystallizes in I4/mcm with a = 5.694 11(7) A, b = 8.0658(2) A, and Z = 4. The oxide and nitride anions are almost completely disordered, as observed when the material is made by nitridation of a pure oxide precursor using ammonia at 900−1000 °C, but contrasting with the full O/N order observed when such nitridation is mineralizer assisted. The detailed structure of Ba2TaO3N is reported for the first time: this compound adopts the K2NiF4 type structure with full O/N order in space group I4/mmm wit...

Polycrystalline samples of Sr3MnRuO7 and Sr2Mn0.5Ru0.5O4 have been synthesized and characterized by neutron diffraction, dc magnetometry, and magnetotransport measurements. They are, respectively, n = 2 and n = 1 members of the Ruddlesden−Popper (RP) An+1BnO3n+1 family; both have tetragonal (I4/mmm) symmetry and a disordered distribution of Ru and Mn over the six-coordinate sites within the perovskite layers of the RP structure. Neither compound shows long-range magnetic order at 2 K, but a spin-glass transition is observed at 16 K (n = 1) or 25 K (n = 2). In the case of the n = 2 compound only, the magnetic transition is accompanied by a reduction in the zero-field electrical conductivity. A maximum magnetoresistance of ∼8% in 14 T is found in both compounds.

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...

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 Ba6Na2Nb2M2O17 (M = P, V), which consists of cubic (c) BaO3 layers and oxygen-deficient pseudocubic (c′) BaO2 layers stacked in the sequence c′ccccc, is presented. In Ba6Na2Nb2M2O17, 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 NbO6 octahedral layers are sandwiched by two single NaO6 octahedral layers, which, in turn, connect with two isolated MO4 tetrahedral layers. Both oxides are derived from the 2:1 ordered perovskite structure (e.g., Ba3ZnTa2O9) by ordered removal of O atoms in every sixth BaO3 layer. Both materials exhibit a relative permittivity of ∼20−23, Q × f0 values of ∼7800−10600 GHz, and negative temperature coefficients of the resonant frequency of ∼−23 to −7 ppm/°C.

The effects of reaction temperature and pO2 were investigated on a series of (Ba,Ca,Nd)FeO3-δ perovskite systems in order to isolate phases containing ordered arrangements of the distinct vacancy and cation ordering patterns identified in less compositionally complex iron oxide systems. Initial synthesis in air at high temperature yields cubic perovskite phases (I) with average iron oxidation states higher than 3; selected area electron diffraction together with diffuse features observed in the synchrotron X-ray diffraction (SXRD) patterns of these materials show evidence of small domains of short-range cation and vacancy order. Annealing these materials in nitrogen or in a sealed tube in the presence of an NiO/Ni buffer yielded the Fe3+ phase Ca2Ba2Nd2Fe6O16 (II), closely related to Sr2LaFe3O8 but with partial cation order as well as anion order present—the larger Ba cations are largely present in the 12-coordinate site between the octahedral iron layers, and Ca is largely present in 10-coordinate sites ...

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.

The new ceramic materials Ba10Mg0.25Ta7.9O30 and Ba10Co0.25Ta7.9O30 have been synthesized in isolation and their dielectric and crystallographic properties characterized fully. The crystal structure determination, using a combination of X-ray and neutron powder diffraction and electron microscopy, reveals a 10-layer perovskite structure that involves the (hcccc)2 stacking sequence with a pair of face-sharing octahedral sites separating three layers of corner-sharing octahedra. The structure is discussed in comparison with the related eight-layer Ba8ZnTa6O24, which involves the (hccc)2 stacking sequence, discovered in an earlier study. The microwave dielectric properties of both materials are determined (Ba10Mg0.25Ta7.9O30 Qf = 33 585 at 4.02 GHz, er = 28, and a temperature coefficient of resonant frequency τf = 30.2 ppm/°C; Ba10Co0.25Ta7.9O30 Qf = 36 693 at 3.78 GHz, er = 30, τf = 28.6 ppm/°C), and factors controlling dielectric behavior in hexagonal perovskites are identified from the available structura...