Search

As a potential cathode material for the ICD lithium battery, one advantage of Ag6Mo2O7F3Cl (SMOFC) is its enhanced gravimetric capacity of ca.133 mAh/g above 3 V (vs Li+/Li) delivered by two biphasic transitions at 3.46 and 3.39 V (vs Li+/Li). The unique crystal structure of SMOFC enables a high silver ion conduction: σ⊥[001]= 3.10−2S/cm (±2.10−2S/cm) and σ//[001]= 4.10−3S/cm (±2.10−3S/cm) and, hence, an excellent discharge rate capability. Lithium insertion has been monitored by in situXRD measurements with HRTEM investigations. There is a linear isotropic collapse of the structure leading to a fully amorphous structure beyond four inserted lithiums.

Mayenite-based oxides [12CaO·7Al2O3] starting from [Ca24Al28O64]4++ 2O2–(insulator) and subsequently annealed so as to obtain [Ca24Al28O64]4++ 4e–(metal) were studied by reflectance and transmission on seven samples with dc conductivities spanning the range 10–10to 1500 Ω–1cm–1. Three of them are essentially insulating. The remaining display an increasing dc conductivity as the electron concentration increases. A set of phonons in the infrared below 0.15 eV and an intense line in the ultraviolet at 6.5 eV account for the optical conductivity of the insulating samples. As the samples become increasingly metallic, we observe an enhancement of spectral weight in the visible range. Simultaneously, the reflectance and the resulting optical conductivity develop a stronger component in the infrared, characteristic of mobile electrons. This electronic response appears to be strongly coupled to the phonons, as shown by their Fano profiles present in the metallic samples. Our results indicate that free carriers promote the formation of polarons and that these two excitations contribute to the dc conducting properties of mayenites. This overall electronic picture is consistent with first principles calculations of the density of states in mayenites. The observed strong electron–phonon coupling may be of interest in view of the superconductivity properties found in the metallic samples.

Biogenic materials are produced by microorganisms and are typically found in a nanophase state. As such, they are difficult to characterize structurally. In this report, we demonstrate how high-energy X-ray diffraction and atomic pair distribution function analysis can be used to determine the atomic-scale structures of MnOxproduced by bacteria and fungi. These structures are well-defined, periodic, and species-specific, built of Mn−O6octahedra forming birnessite-type layers and todorokite-type tunnels, respectively. The inherent structural diversity of biogenic material may offer opportunities for practical applications.

The delafossite structure (ABO2) accommodates a wide range of transition and rare-earth cations on the B-site in combination with a short list of A-site cations. This paper reports the effects on defect chemistry and transport as a function of the B-site cation in copper-based delafossite materials, with CuScO2 and CuYO2 as examples. Large B-site cation delafossites exhibit small polaron conduction, a diffusion-limited conduction mechanism, with an activation energy approximately twice that of CuAlO2 (0.22 eV vs 0.14 eV, respectively). The mobility for these materials is found to be <1 cm² V^-1 s^-1, further evidence of small polaron conduction. The majority defect species is highly dependent on the B-site cation, such that CuScO2 and CuYO2 are dominated by extrinsic defects (acceptor doping) and free oxygen interstitials, whereas off-stoichiometry dominates CuAlO2. Dopant solubility is shown to be 1% for bulk CuScO2 samples and lower in CuYO2.

CuAlO2 exhibits a unique defect structure that is dependent on the synthesis route. High-temperature solid-state and low-temperature hydrothermal techniques are compared to illustrate how cation off-stoichiometry affects the electrical properties of CuAlO2. A defect complex of Al on a Cu-site stabilized by two bound oxygen interstitials (AlCu^••2Oi‘ ‘)‘ ‘ is proposed which serves as an acceptor dopant to set the hole concentration. Trapping of holes (small polarons) by such complexes with decreasing temperature is proposed to account for the decreasing carrier content with temperature. Hydrothermal samples exhibit approximately an order of magnitude increase in hole concentration relative to the solid-state synthesized samples; this is reflected in the electrical conductivity and may explain the variations in electrical properties reported for CuAlO2.

Ceramic samples of LaSr2Fe3-yCryO8+δ (y = 0, 0.3, 0.6, and 1.0) were characterized with X-ray powder diffraction, thermal gravimetry, dilatometry, and total conductivity measurements in the temperature range 750−950 °C at oxygen partial pressures between 10^-22 and 0.5 atm. When prepared in air, the doped ferrites adopt rhombohedral R&thremacr;c structure. The loss of oxygen from the crystal lattice results in formation of the vacancy-ordered orthorhombic structure LaSr2Fe3O8 for the parent ferrite at temperatures above 750 °C and oxygen pressures below about 10^-5 atm while chromium substituted samples retain the rhombohedral structure. The isothermal ion conductivity is found to decrease with the increase in chromium doping from y = 0 to y = 0.6. However, an increase in the chromium content to y = 1 results in an increase in the oxygen ion conductivity to about 0.2 S/cm. This behavior is explained with a model where the oxygen ions coordinated to chromium are not excluded entirely from the transport mechanism.

The cosubstituted solid solution In2-2xSnxZnxO3-δ was acceptor-doped with Zn²⁺ to form In2-x-ySnxZnyO3-δ (y > x). A 4% Zn²⁺ “excess” can be introduced in In1.6Sn0.2Zn0.2O3-δ while maintaining the bixbyite structure. The n-type conductivity of the doped material decreases with zinc substitution. Zn-doped In1.6Sn0.2Zn0.2O3-δ was annealed under high oxygen pressure (~170 atm) to eliminate anion vacancies, VO^{••. Owing to a decrease in carrier concentration by up to 2 orders of magnitude from 1020 to 1018 carriers/cm3, the conductivity of the annealed material decreases. Hall measurements show that the carriers remain as n-type. The results imply the existence of neutral Zn−VO•• complexes that prevent the donation of holes by Zn2+.}

The electrical conductivity, Hall effect, and thermoelectric coefficient of Zn/Sn-cosubstituted In2O3 (In2-2xSnxZnxO3-δ), undoped In2O3, and indium−tin oxide (ITO) were studied vs cation composition, state of reduction, and measurement temperature (over the range of 4.2−340 K). Carrier contents and mobilities were determined from the Hall coefficient and conductivity in each case. In2-2xSnxZnxO3-δ displays conductivities up to 1 order of magnitude lower than ITO, and the conductivity of the material decreases with increasing cosubstitution, from approximately 860 to 235 S/cm. Reduction of the materials under flowing H2/N2 increases their carrier concentrations and therefore their conductivities. These results are discussed in terms of possible defect and transport models.

Organic chromophores crystallizing in nonpolar space groups (P&onemacr;) have been converted to polar structures (P1) by solid solution symmetry reduction to produce materials with measurable SHG signals. Here, the inorganic compound Cu(NC5H5)4NbOF5 is used to demonstrate that solid solution symmetry reduction depends on molecular recognition of the guest species at crystal growth faces. In the solid solution Cu(NC5H5)4[(NbOF5)1-x(WO2F4)x] (0 ≤ x ≤ 1) the [WO2F4]^2- guest molecular ions disrupt the local symmetry, but owing to the lack of recognition of guest anions at the crystal growth surfaces, the full three-dimensional structure retains the host's symmetry.

Composition space diagrams can be used to study the stability and variety of mixed transition metal oxide fluorides prepared under hydro(solvato)thermal conditions. Prior to this work the neutral (CuF(NC5H5)4)2NbOF5 cluster had not been observed but it was expected because of the nucleophilic character of the oxygen and trans fluorine in the [NbOF5]^2- species. [H3O]2[(CuF(NC5H5)4)2NbOF5][F]2, a compound containing the 2:1 (Cu:Nb) cluster, was synthesized from the concentration variables, [CuO·0.5 Nb2O5], [(HF)x·pyridine], and [H2O], by adding a fourth, [pyridine], and extending the composition space from a two-dimensional triangle to a three-dimensional prism. Crystal Data:  [H3O]2[(CuF(NC5H5)4)2NbOF5][F]2, tetragonal, space group I41/acd (no. 142), with a = 24.691(1) Å, c = 14.556(1) Å, Z = 8.

A novel transparent conducting spinel solid solution Cd1+xIn2-2xSnxO4 (0 ≤ x ≤ 0.75 at 1175 °C) between cubic CdIn2O4 and orthorhombic Cd2SnO4 has been discovered. The extent of this solid solution is noteworthy given that bulk phase relations determined in air over the temperature range 800−1175 °C demonstrate that cubic (spinel) Cd2SnO4 is metastable. Reduced samples exhibit exceptional four-point dc conductivities exceeding 3500 S/cm (x = 0.70). The maximum optical gap estimated from diffuse reflectance spectra is ~3.0 eV for 0 ≤ x ≤ 0.15. The optical gap shows negligible change with reduction, possibly because of combined Moss−Burstein and band-narrowing effects. Abrupt conductivity increases and optical gap decreases at specific compositions, i.e., x = 0.4 and 0.2 respectively, may be indicative of a change in cation distribution between tetrahedral and octahedral sites. Room temperature thermopower measurements indicate the change in conductivity across the solution is a consequence of an increase in carrier density and that mobility remains relatively constant.

The stabilities of charge carriers, the transport properties, and the defect structures of the layered, quadruple perovskite La2Ba2Cu2Sn2O11 have been investigated by chemical substitutions, powder X-ray diffraction, and simultaneous high-temperature electrical conductivity and thermopower measurements. The in-plane copper−oxygen bond lengths, in cooperation with the copper-coordination environment, are observed to control the chemical solubilities, stable charge carrier species, and oxygen defects. Potential n-type substitutions are successful via the substitution of niobium for tin. However, oxygen defects are demonstrated to be important compensation species for the incorporation of the substituted cations and in the mediation of the charge carrier concentration with the ambient atmosphere in the near-synthesis temperature region. These materials are intrinsic semiconductors and display crossover from n-type to p-type behavior with increasing oxygen partial pressure, from 10^-5 to 1 atm pO2, in the temperature range from 600 to 800 °C. Furthermore, the transport parameters are shown to be composition-dependent for these compounds and asymmetric with respect to electron and electron−hole conduction, in contrast to other layered copper oxides. Specifics of the inner architecture of layered copper oxides, particularly residual internal stresses between layers, are discussed with respect to their control over the redox behavior of copper−oxygen networks, and the implications of these findings are elaborated on with respect to the realization of new n-type superconductors.

The phase relations in the system MgO-V₂O₅-MoO₃ were studied and the subsolidus region of the phase diagram was constructed. The new compound Mg_2.5VMoO₈ was discovered on the join of MgMoO₄-Mg₃V₂O₈. Mg_2.5VMoO₈ crystallizes in the orthorhombic space group Pnma (No. 62) with cell dimensions a = 5.0515(1) Å, b = 10.3455(2) Å, c = 17.4683(4) Å, and Z = 6. The structure is a framework of MoO₄ and VO₄ tetrahedra with linking octahedral and trigonal prismatic MgO₆ groups. The molybdenum and vanadium cations preserve their highest oxidation state, and the electrical neutrality of the crystalline lattice is maintained by partial occupancy of magnesium sites. Simple quasibinary equilibria were established between MgMoO₄ and MoV₂O₈, V_2-xMo_2xO₅, MgV₂O₆, and Mg₂V₂O₇. Copyright 1994, 1999 Academic Press

A new compound, La1-xSr1+xCuGaO5 (0.10

In2O3 exhibits a dramatic increase in solubility of SnO2 and ZnO when they are cosubstituted into In2O3. The resultant material, In2-2xSnxZnxO3-δ with x = 0−0.4, displays the same order of magnitude conductivity and transparency compared with bulk ITO (tin-doped indium oxide). Rapid quenching of In2-2xSnxZnxO3-δ raises the conductivity and widens the optical bandgap while lowering the optical transmission.

The mechanism of cation replacement in the Li1-xHxAlO2; 0.00 ?x ? 0.90 system was investigated with XRD. Examination of the peak position and intensity associated with the 018 and 110 Bragg reflections $$(R\bar 3m)$$ in a series of partially replaced samples showed that the cation replacement process proceeded by a two phase mechanism. Catalytic characterization of aLiAlO2 with the 2-propanol probe reaction revealed the formation of the condensation products methyl-cyclopentene, 4-methyl-2-pentanone, and 4-methyl-2-pentanol. These products were seen in addition to propylene and acetone. Catalytic characterization of Li1-xHxAlO2;x = 0.90 with 2-propanol showed a significant decrease in condensation activity and no change in the propylene/acetone ratio relative to aLiAlO2. This suggests that the decrease in the amount of lithium eliminated the basic sites necessary for the condensation reactions.

Noncentrosymmetric materials are of special interest in materials chemistry owing to their technologically important properties, such as ferroelectricity and second-order nonlinear optical behavior. Over 500 noncentrosymmetric oxides have been compiled and categorized by symmetry-dependent property and crystal class. In addition, the materials are described by their transition, or main group, metal coordination environment and grouped by element. Similarities within and between groups are discussed, as are noncentrosymmetric structure−property relationships.

The structure of LaSr2CuTiO6.5, a novel (ABO3)nAO n = 2 Ruddlesden−Popper phase, has been solved by powder X-ray diffraction and electron microscopy. The diffraction patterns are consistent with I4/mmm symmetry, with tetragonal lattice parameters a = 3.8816(1) Å and c = 20.296(2) Å. The structure of LaSr2CuTiO6.5 is similar to Sr3Ti2O7, with copper and titanium disordered over the single B-cation site, and lanthanum and strontium almost perfectly disordered over the two A-cation sites. The oxygen content, determined by thermogravimetric reduction to be 6.5 (±0.1), is consistent with divalent copper with the oxygen vacancies distributed within the perovskite layers. The absence of local order and strategies for inducing a layered arrangement of the B-cations are discussed.

Composite solid oxide fuel cell (SOFC) anodes consisting of LaSr2Fe2CrO3-δ(LSFeCr) and Gd0.1Ce0.9O2-δ(GDC) were evaluated during operation on H2, H2O-Ar-H2, CO, and CO-H2mixtures. Impedance spectroscopy studies showed three different electrode processes that varied in importance with temperature and fuel composition. The primary impedance response peaked at ∼2 Hz and followed a similar dependence on H2partial pressure in both H2-H2O-Ar and H2–CO mixtures. The total anode polarization resistance at 800°C increased by a factor of ∼2 on going from pure H2fuel to pure CO.

The title compound is hydrothermally prepared from a mixture of Ag2O, MoO3, 4‐hydroxypyridine, HF, HCl, and H2O in the molar ratio of 2:2:5:30:4:4 (autoclave, 150 °C, 24 h, 72% yield).

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Solid solutions of LiAlxCr1‐xO2 are synthesized over the whole composition range (0 ≤ x ≤ 1.0) by reaction of Li2CO3, boehmite (Al(OOH)), and Cr2O3at ∼600 °C (2‐5 d) and subsequent heating at 700‐1000 °C. The Al‐rich phases (x > 0.6) are obtained for the first time.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.