Simulation of ion transport in layered cuprates La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>CuO<Subscript>4 − <Emphasis Type="Italic">δ</Emphasis></Subscript>

The processes of oxygen diffusion in La_{2 ? x} Sr _x CuO_{4 ? δ} phases have been simulated for the first time by the molecular-dynamics method. Calculations were performed for the temperature range 300–2500 K. The behavior of the radial pair correlation functions, which characterize the degree of order of O1 ions in CuO₂ layers, indicates that O^2? anions form a weakly correlated subsystem within a CuO₂ layer. To quantitatively confirm the conclusions about the predominantly two-dimensional character of ion transport and different mobilities of O1 and O2 particles in the cuprates under study, the pair oxygen diffusion coefficients in the La_{2 ? x} Sr _x CuO_{4 ? δ} lattice were calculated. It is shown that oxygen diffusion occurs through the conventional hopping mechanism mainly in CuO₂ layers; correspondingly, the diffusion coefficient for equatorial ions (O1) exceeds that for apical oxygen anions (O2) by an order of magnitude. The motion of oxygen anions was traced at the microscopic level through analysis of the particle transport trajectories. It has been proven for the first time that diffusion of O1 ions in the ab plane in a nonstoichiometric LaSrCuO_3.61 sample occurs through jumps to the nearest position or along CuO₂ layers; in a more complicated way, it may occur through unoccupied O2 lattice sites.     

Microstructure and dielectric properties of La2O3 films prepared by ion beam assistant electron-beam evaporation

Ultrathin La₂O₃ gate dielectric films were prepared on Si substrate by ion assistant electron-beam evaporation. The growth processing, interfacial structure and electrical properties were investigated by various techniques. From XRD results, we found that the La₂O₃ films maintained the amorphous state up to a high annealing temperature of 900 °C for 5 min. From XPS results, we also discovered that the La atoms of the La₂O₃ films did not react with silicon substrate to form any La-compound at the interfacial layer. However, a SiO₂ interfacial layer was formed by the diffusion of O atoms of the La₂O₃ films to the silicon substrate. From the atomic force microscopy image, we disclosed that the surface of the amorphous La₂O₃ film was very flat. Moreover, the La₂O₃ film showed a dielectric constant of 15.5 at 1 MHz, and the leakage current density of the La₂O₃ film was 7.56 × 10⁻⁶ A/cm² at a gate bias voltage of 1 V.     

Synthesis and crystal structure of hexaaquamagnesium hydrogen phosphododecatungstate tetrahydrate [Mg(H2O)6][HPW12O40]·4H2O

Crystals suitable for X-ray structure analysis were obtained after the slow evaporation of the reaction mixture containing equimolar quantities of magnesium chloride and dodecatungstophosphoric acid aqueous solution insuring pH of the solution between 1.0 and 1.2. This simple synthetic route yielded stability of Keggin anion and high quality [Mg(H₂O)₆][HPW₁₂O₄₀]·4H₂O single crystals. The obtained compound belongs to the group of heteropoly compounds and its structure is composed of Keggin [PW₁₂O₄₀]^3– anions, [Mg(H₂O)₆]²⁺ cations and lattice water molecules. Zigzag arrangement of Keggin anions along c-axis creates irregular channels occupied by [Mg(H₂O)₆]²⁺ cations and lattice H₂O molecules. The calculation of the total potential solvent volume indicated the presence of 4.1 lattice H₂O lattice molecules per formula unit, which is in agreement with the here presented structural model. The position of one lattice water molecule is well defined, while each of three other molecules is statistically distributed over two locations. Hydrogen bonds involve all coordinated and lattice H₂O molecules, as well as some oxygen atoms from the Keggin anion. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Phase Formation,Crystal Structure and Electrical Properties of La212 Type Compound Substituted by Silver or Praseodymium

The La212 type compounds substituted by silver or praseodymium are prepared by solid state reaction method. It is found that compounds La_2‐xSr_xCa_0.5Pr_0.5Cu₂O₆, La_1.6Pr_0.4Ca_1‐xSr_xCu₂O₆ and La_2‐xPr_xCa_0.5Sr_0.5Cu₂O₆ can be formed for x=0.4‐1.1, 0‐0.5 and 0‐1.5, respectively. A new member of La212 type compounds, La_2‐xAg_xCaCu₂O₆ is also prepared. Their structures are verified by Rietveld structure refinement to belong to the structure type of La212 cuprate oxide with space group I4/mmm. Their electrical properties are investigated. La_1.65Ag_0.35CaCu₂O₆ displays metal‐like behavior and its resistivity decreases with the decrease of temperature from 300K to 4.2K.     

Crystal structure of a new neodymium hexamolybdotellurate,Nd<Subscript>2</Subscript>TeMo<Subscript>6</Subscript>O<Subscript>24</Subscript> · 19H<Subscript>2</Subscript>O

The crystal structure of a new compound, namely, Nd₂TeMo₆O₂₄ · 19H₂O, is determined using X-ray diffraction. The crystal has a chain structure and consists of [Nd₂TeMo₆O₂₄ · 14H₂O]_n neutral chains aligned parallel to the [010] direction and crystallization water molecules. In a chain, each Nd atom links two heteropoly anions. The Nd³⁺ environment includes seven water molecules and two oxygen atoms of the two heteropoly anions adjacent in the chain. The polyhedron is a monocapped tetragonal antiprism. In the previously studied complex of similar composition, namely, Nd₂TeMo₆O₂₄ · 18H₂O, the Nd coordination polyhedron has the shape of a tricapped trigonal prism formed by six water molecules and three oxygen atoms of the two heteropoly anions adjacent in the chain.     

Microwave dielectric properties of La(1‐2x/3)Bax(Mg0.5Sn0.5)O3 ceramics

This study examined the potential applications of microwave dielectric properties of La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics in rectenna. The La_(1‐2x/3)Ba_x(Mg_0.5Sn_0.5)O₃ ceramics were prepared by the conventional solid‐state method with various sintering temperatures. An apparent density of 6.62 g/cm³, a dielectric constant of 20.3, a quality factor of 51,700 GHz, and a temperature coefficient of resonant frequency of ‐78.2 ppm/K were obtained for La_2.98/3Ba_0.01(Mg_0.5Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Single-crystal structure of vanadium-doped La2Mo2O9

A high-precision X-ray diffraction study of single crystals of two compositions—La₂Mo_1.78V_0.22O_8.89 and La₂Mo_1.64V_0.36O_8.82—was performed. In the vanadium-doped compounds, as in the structure of the metastable β_ms phase of pure La₂Mo₂O₉, the La and Mo atoms and one of the three oxygen atoms are displaced from the threefold axis, on which they are located in the high-temperature β phase. The structure contains two partially occupied oxygen sites. It was shown that molybdenum atoms are partially replaced by vanadium atoms, which are not involved in the disordering, are located on the threefold axis, and are shifted toward one of the oxygen atoms. This is consistent with the temperature-induced changes in the structure of La₂Mo₂O₉ and the changes in the properties of these crystals caused by the introduction of vanadium atoms into the structure.     

Photoluminescence of annealed LLGG:Cr3+ crystals under high pressure

High pressure photoluminescence has been used for analysis of lattice disorder in La_2.7Lu_2.29Cr_0.01Ga₃O₁₂ and La_2.32Lu_2.59Cr_0.02Ga_3.07O₁₂ crystals. Photoluminescence of samples before annealing and those annealed for 5 h in oxygen and hydrogen atmosphere at 923 K has been measured. The pressure dependence of Cr³⁺ luminescence has been used to obtain the crystal field distribution (lattice disorder) and its dependence on the thermal treatment. The distribution energy of the ⁴T₂ state has been considered as a measure of disorder. Annealing in oxygen has been found to reduce the energies of ⁴T₂ states for all sites, and annealing in hydrogen – to increase these energies.     

Synthesis and Characterization of Ml2-Intercalated Bi-2212 Cuprates (M=Mn,Fe, Co,Cu, Zn)

Abstract

A series of new layered cuprates with the composition MI_2+xBi₂Sr₂CaCu₂O_8+y (x=0.6–0.9; M=Mn, Fe, Co, Cu, Zn) have been synthesized by the reaction of Bi₂Sr₂CaCu₂O₈ with each transition metal under an atmosphere of iodine at 400°C. The new cuprates, lamellar in shape, are crystallized in a tetragonal unit cell with the lattice parameters of a = 5.393–5.402 Å and c = 43.32–43.96 Å. A structure model for these cuprates are proposed in which the monoiodide anions are intercalated in the Bi₂O₂ layer to form a bilayer accompanying 3d metal cations. All of the intercalated cuprates are non-superconducting to be as high as 0.74–2.52 MΩ · cm in resistivity at room temperature.     

Refinement of the crystal structure of calcium-lithium-aluminum tourmaline from the pegmatite vein in the Sangilen Upland (Tuva Republic)

The crystal structure of a natural calcium-lithium-aluminum tourmaline, which has the unique composition (Ca_0.62Na_0.32□_0.06)(Al_1.08Li_0.99Fe _0.66 ²⁺ Mg_0.24Ti_0.03)Al₆[Si₆O₁₈](BO₃)₃(OH_2.28O_0.72) · (F_0.84O_0.16), is refined (R = 0.019, R _w = 0.022, S = 1.47). It is found that the O(1)(W) site is split into two sites, O(1) and O(11), which are incompletely occupied by fluorine and oxygen anions, respectively, and that the O(3)(V) site contains bivalent oxygen anions. The solid solution studied is close in composition to the liddicoatite mineral species and differs from the latter one by the Li: Al ratio in the Y octahedra and the presence of bivalent oxygen anions in the O(3) site. The tourmaline studied differs from the hypothetical oxyliddicoatite by the population of the O(1)(W) site by fluorine and accommodation of additional oxygen anions in the O(3)(V) site.     

Cation clustering and formation of free oxide ions in sodium and potassium lanthanum silicate glasses: nuclear magnetic resonance and Raman spectroscopic findings

Alkali silicate glasses containing lanthanum oxide are useful model systems for understanding the structural role of rare earth cations in optical and other types of materials. We report ²⁹Si and Raman spectra of sodium and potassium silicate glasses, both with added La₂O₃ and with La₂O₃ substituted for Na₂O or K₂O on an equal-oxygen basis. In the former series, silicate speciation changes show the formation of more non-bridging oxygens (NBO) as more of the network-modifying La₂O₃ is added. In the latter series, however, in which the nominal ratio of NBO to Si is constant, silicate speciation changes indicate that the actual ratio decreases significantly as La is substituted for 3 Na or K. The simplest explanation of this finding is that up to several percent of the oxygen in the La-rich glasses is not bonded to any Si, but instead forms `free oxide' ions that are part of La-rich domains. Although the size of these domains remains unconstrained, the lack of evidence for phase separation and continuity of trends in structure with composition suggests that the metastable liquid structure at the glass transition contains substantial intermediate-range heterogeneity.     

A partial molar volume for La2O3 in silicate melts

The densities of several La-bearing silicate melts distributed along binary joins have been measured using the double-bob Archimedean method. The results show that the addition of La₂O₃ leads to an increase in the melt density. From these density data, the partial molar volume of La₂O₃ in silicate melts has been determined. Distinct values for partial molar volume of La₂O₃ have been obtained (i.e., 44.01 and 37.04 cm³/mol at 1273 K for the La₂O₃-Na₂O-SiO₂ and La₂O₃-CaO-MgO-Al₂O₃-SiO₂ systems, respectively) indicating a compositional dependence of the partial molar volume of La₂O₃. Nevertheless, a single value for the partial molar volume of La₂O₃ (i.e., 43.47 cm³/mol at 1273 K) suffices to describe the molar volume of melts within errors in the entire multi-component system La₂O₃-Na₂O-CaO-MgO-Al₂O₃-SiO₂ and for La₂O₃ concentrations not greater than 7 mol%. In addition, this work points out that the molar volumes behave ideally within the composition range investigated (i.e., linear variation of the molar volume along the binary joins). Distinct values for the partial molar volume of La₂O₃ obtained in this study and their differences with the molar volumes of molten La₂O₃ given in the literature raise the possibility however that this ideality is not maintained within the entire system.     

Specific features of the structure and weight loss of aliovalent-substituted oxides based on lanthanum gallate (La,Sr)(Ga,Fe,Mg)O3 − y

The structure of the (La_0.9Sr_0.1)(Ga_0.56Fe_0.24Mg_0.20)O_{2.85 + y} oxide is investigated using neutron powder diffraction at temperatures of 10, 295, and 1000 K. The results of the structure refinement are in good agreement with the dilatometric and thermogravimetric data and confirm the inference that the valence state of iron cations is higher than 3+ and that the lattice undergoes an additional expansion due to the oxygen loss at temperatures above 870 K.     

Epitaxial growth of β-Ga2O3 nanocolumns on MgO substrate

Crystal structure of Ga₂O₃ nanocolumns grown on MgO substrate is analyzed by electron microscopy and electron diffraction study. The nanocolumns have β-Ga₂O₃ structure and the growth direction is [0 0 1] directions. A thin γ-Ga₂O₃ layer grows on the substrate to relax the lattice misfit between MgO and β-Ga₂O₃. The bottom layer of the γ form layer is disordered by {1 1 0} stacking faults. Poly crystalline structure that consists of β-Ga₂O₃ and γ-Ga₂O₃ nanocrystals exists between the β form nanocolumns and the γ form layer. The γ form changes gradually to the β form growing up to the nanocolumn. Though various crystal forms appear in a specimen, oxygen cubic close-packed lattice in crystal structures has always the same orientation in all layers including the MgO substrate.     

New Regioselective Intercalation Reactions

Abstract

The ordered layered double hydroxide, [LiA1₂(OH)₆]CI. 2H₂O exhibits shape-selective ion-exchange intercalation of dicarboxylate anions. Specific isomeric preferences can be controlled by varying the reaction temperatures. The intercalated guests can be quantitatively recovered from the host lattice with concomitant regeneration of the host offering a novel approach in separation science. To illustrate the potential of this new material in separation science, we describe the isolation of pure 1,4-benzenedicarboxylate and 2, 6-naphthalenedicarboxylate from mixtures of their isomers. The neutral organic acids are both monomers in the synthesis of a range of important polyesters.     

Computer simulation of ion transport in a new cathode material PrSrCuO4-δ

Oxygen diffusion in the new class of cuprates Pr_2-x Sr _x CuO_4-δ (x = 1) with perovskite structure has been simulated in the temperature range of 300–2100 K for the first time. A calculation has shown the presence of anisotropy of oxygen motion: the oxygen transport in PrSrCuO_3.7 in the temperature range of 300–2100 K is mainly two-dimensional, with an activation energy of no more than 0.40 eV. The coefficient of thermal expansion of PrSrCuO_3.7 (9.9 × 10^?6 K^?1 in the range 1300–2100 K) and the oxygen diffusivity in it, which exceed the corresponding values for La_2-x Sr _x CuO_4-δ, indicate that this compound is promising as an electrode material with a mixed ionic-electronic conductivity for various electrochemical devices. The results expand the previous concepts of the oxygen-ion transport in complex cuprates.     

Crystal structure of the cubic β<Subscript>ms</Subscript>-phase of a La<Subscript>1.82</Subscript>Bi<Subscript>0.18</Subscript>Mo<Subscript>2</Subscript>O<Subscript>9</Subscript> single crystal at 33 K

Single crystals of the cubic β_ms-phase of La_1.82Bi_0.18Mo₂O₉ have been characterized for the first time by precision X-ray diffraction at 33 K. The structure of a crystal determined at T = 33 K is identical to the structure studied at room temperature. It is confirmed that the La, Mo1, and O1 atoms deviate from their positions on the threefold axis in the high-temperature β-phase; part of lanthanum atoms is substituted by bismuth atoms, which are located on the threefold axis; part of the molybdenum atoms return to the position on the threefold axis.     

Synthesis, structure and characterization of a new inorganic-organic hybrid complex (C3H5N2)2[Cd(C3H4N2)2Nb2O3F8]·2H2O

(C₃H₅N₂)₂[Cd(C₃H₄N₂)₂Nb₂O₃F₈]·2H₂O (C₃H₄N₂=imidazole) (1) was prepared from the hydrothermal reaction of Nb₂O₅, 3CdSO₄·8H₂O, C₃H₄N₂, HF and H₂O at 403 K, and characterized by single crystal X-ray diffraction and IR spectra. 1 crystallizes in the orthorhombic system, space group Pba2, with a=11.0192(9), b=16.8012(14), c=6.8717(6) ?, and Z=2. The crystal is made up of [Cd(C₃H₄N₂)₂Nb₂O₃F₈]²⁻ anions, [C₃H₅N₂]⁺ complex cations and H₂O molecules of crystallization. And the backbone of the compound is a one dimension coordination polymeric chain containing the anions. The complex cations and anions are linked through hydrogen bonding interactions. Co-crystallized water molecules fill in the pores and hydrogen bond to the host. Bond valence sums show that O1, O3 and F3 have much more negative charge, which are in agreement with the crystal structure that they act as bridging atoms.Supplementary material CCDC-606794 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge at http://www.ccdc.cam.ac.uk/ const/retrieving.html or from the Cambridge Data Centre (CCDC), 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44(0)1223-336033 or e-mail: deposit@ccdc.cam.ac.uk.     

Precipitation of nanometer-sized SnO2 crystals and Sn depth profile in heat-treated float glass

The effect of oxygen diffusion from the atmosphere on tin depth profile in the bottom face of a soda-lime-silica float glass at temperatures above T_g was investigated. The heat treatment was performed in ¹⁸O₂/N₂ and argon (Ar) atmospheres. The significant diffusion of tin to the surface was observed for the glass heat-treated in ¹⁸O₂/N₂ atmosphere, resulting in the formation of a tin-enriched layer near the surface region. It was found that the tin was supplied from the region shallower than the ‘hump’ which is commonly observed in the tin profile of a commercial soda-lime-silica float glass. No significant change in the tin depth profile was observed for the glass heat-treated in Ar atmosphere. These results indicate that ¹⁸O diffusion into the glass, which causes the change in chemical state of tin from Sn²⁺ to Sn⁴⁺, induces the significant diffusion of tin. Furthermore, the precipitation of crystalline SnO₂ particles with a diameter of ∼1 nm was clearly recognized in the tin-enriched layer. This fact indicates that a phase separation was induced by the oxygen diffusion into the glass. Consequently, Sn²⁺ may be supplied to the surface in order to compensate for the marked decrease in Sn²⁺ concentration in the glass system. The significant diffusion of tin to the surface was suppressed by increasing the iron content in the glass. This suppression was ascribed to the increase in Sn⁴⁺ concentration as a result of the redox reaction between tin and iron because the diffusion coefficient of Sn⁴⁺ is much smaller than that of Sn²⁺.     

Crystal structure, vibrational spectra, and thermal decomposition and nitrogen adsorption behaviour of a new tetramanganese(II) dipyrophosphate decahydrate, Mn4(P2O7)2·10H2O

A new manganese(II) pyrophosphate, Mn₄(P₂O₇)₂·10H₂O, has been synthesized and characterized by single-crystal X-ray diffraction [orthorhombic space group Pnma, with unit cell parameters of a=9.3288(3) ?, b=25.9532(9) ?, c=8.4783(3) ?; Z=4]. All the pyrophosphate anions show non-linear P–O–P bonds with an average angle of 128.60°. The framework of this new pyrophosphate is made up of packed layers of MnO₆ octahedra connected by double-tetrahedra P₂O₇ groups and a layer of Mn(H₂O)₆ units. The [P₂O₇]⁴⁻ anions adopt a bent, near-staggered conformation. The absence of coincidences for the majority of the IR and Raman bands is in accord with the centrosymmetric structure of the material. The vibrational spectra have been interpreted in part on the basis of factor group effects. The structural changes occurring during heating have been investigated by TG-ATD. When Mn₄(P₂O₇)₂ ^.10H₂O is gradually heated, it decomposes into an intermediate hydrated salt at 96°C and then to anhydrous Mn₂P₂O₇ at 325°C. This thermal behaviour is different from that of Zn₄(P₂O₇)₂·10H₂O. The crystal structure of the new managenese(II) pyrophosphate is compared with the known structures of Zn₄(P₂O₇)₂·10H₂O, Mn₂P₂O₇·2H₂O and anhydrous Mn₂P₂O₇. The adsorption and desorption isotherms of Mn₄(P₂O₇)₂·10H₂O, Zn₄(P₂O₇)₂·10H₂O and MnKHP₂O₇·2H₂O have been investigated by BET measurements and the results show that the capacity for N₂ sorption of the Mn(II) salt is two times lower than is that of the Zn(II) isotype and two or three times higher than is that of MnKHP₂O₇·2H₂O.