Tetramethylammonium (TMA) polyoxovanadates have been precipitated from aqueous solutions aroundpH 7. Decavanadate clusters (TMA)4[H2V10O28]•4H2O are formed at room temperature whereas a layered (TMA)[V4O10] mixed valence compound is formed under hydrothermal conditions. 51V NMR spectra recorded on the solution at different temperatures show that upon heating decavanadate clusters are progressively transformed into cyclic [V4O12]4− metavanadates. This suggests that the mixed valence polyoxovanadates are formed via the ring opening polymerization of metavanadate precursors.

For extended magnetic solids containing several unpaired spins per spin site, we reviewed briefly recent progress in quantitative and qualitative methods of describing their spin exchange interactions on the basis of electronic structure calculations for their spin dimers.

Manganese dioxides have received much attention over the last two decades as ion exchangers. Actually these are typically mixed-valence compounds and the terminology of ‘dioxide’ is not appropriate. The mechanisms for their variety of chemical reactivities are still open for study. On the cation uptake mechanism there are strong claims that a redox process is involved in cation uptakes by manganic acids synthesized by substituting H+ for alkali cations incorporated in ‘hydrous manganese dioxides’. The present work was carried out to physically demonstrate the alkali cation exchange mechanism on tunnel-structured manganic acids and to study the ion exchange with lattice vibrational spectroscopy. Manganic acids were prepared through the redox process using KMnO4 and MnSO4, and thermal decomposition of (CH3)3COK and MnCO3 at 530°C. ESCA spectra of their alkali cation exchanged forms indicated no evidence of redox process and supported the ion exchange mechanism on these materials. Their infrared absorption spectra strongly depended on their preparation routes and are closely related to their ion-exchange selectivity of each material. Thus, the vibrational spectra of manganic acids take an important role as a synthesis index together with XRD patterns.

A combined approach, using solid state NMR and Molecular Dynamics (MD) simulations, has been employed in this work to investigate fluoride-ion motion in the PbSnF4 family of anionic conductors, materials that contain double layers of Sn2+ and M2+ cations. 19F MAS NMR spectra of PbSnF4 and BaSnF4 show that the fluoride ions are mobile on the NMR timescale (10−4 s), even at room temperature. In the case of BaSnF4, two different groups of fluoride ions were observed, one group corresponding to fluorine atoms between the layers of Ba2+ cations, and the other set, corresponding to mobile fluoride ions undergoing exchange between sites in the Ba-Sn and Sn-Sn layers. The 119Sn NMR suggests a highly distorted Sn environment in these compounds, consistent with the presence of stereoactive Sn lone pairs. MD simulations, using the Polarizable Ion Model, have been carried out to probe the conduction mechanism. These simulations are able to reproduce elements of the structure such as the reduction in the occupancy of the fluorine ions between the Sn-Sn layers. Anisotropic conductivity, involving primarily motion in the M-Sn layers, is predicted, consistent with the NMR results. In the case of BaSnF4, no motion involving the fluoride ions in the Ba-Ba layers is observed on the simulation timescale (10−12 s) and a cyclic mechanism of fluoride-ion motion involving two types of fluoride ions in the Ba-Sn layers is proposed.

Layered Co1-yNiyO2-δ oxides with 0≤y≤1 have been synthesized by chemically extracting lithium from LiNi1-yCoyO2 with NO2PF6 at ambient temperature. The samples have been characterized by X-ray diffraction, wet-chemical analyses, infrared spectroscopy, and magnetic susceptibility measurements. While NiO2-δ retains the initial O3 (CdCl2 structure) layer structure of LiNiO2, CoO2-δ consists of a mixture of P3 and O1 (CdI2 structure) phases that are formed by a sliding of the oxide ions in the initial O3 structure. CoO2-δ and NiO2-δ have oxygen contents of, respectively, 1.67 and 1.95 and the oxygen content increases with increasing Ni content, y, in Co1-yNiyO2-δ. While CoO2-δ exhibits metallic conductivity as revealed by theabsence of absorption bands in the infrared spectrum, NiO2-δ exhibits semiconducting behavior due to a completely filled t2g band. Magnetic data reveal a transition from antiferromagnetic to ferromagnetic correlations as the Ni content in Co1-yNiyO2-δ increases.

(CaxPb10−x)(VO4)6F2 apatites were synthesised and their microstructures were studied using powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy before and after leach testing. X-ray diffraction showed that the apatites were hexagonal with a ≍ 10Å and c ≍ 7Å. During the leach test, Pb was released into the solution more slowly than Ca, which is desirable as the immobilisation of Pb is of importance. The experimental results also showed that V was almost undetectable in the leaching test solutions. In the (Ca7Pb3)(VO4)6F2 pellet, Ca and Pb distributions were not homogenous from one grain to another. Microstructural evidence from scanning electron microscopy revealed that the dissolution via development of etch pits began at grain boundaries and inside grains, and progressed faster in Ca rich regions. These results suggest that apatites of high Pb to Ca ratio are more durable.

Ferroelectric triglycine sulphate crystals have been grown under the influence of an intense electric field of 6×104 V/m. Relative to crystals grown under ambient conditions (TGS) the crystals grown under the electric field (TGS-E) display a dielectric permittivity a factor of two lower. Significant differences are observed in the Curie-Weiss behavior of the ferroelectric phase, in the x-ray diffraction patterns and in the differential calorimetry measurements.

The compound (H3O)1.5{[VO(H2O)]PO4}3·2.5H2O is a new member of a series of vanadium phosphates containing vanadium in both plus four and five oxidation states. Charge ordering occurs in these mixed vanadium phosphate layered compounds forming striped phases with different periodicities. The VOPO4 layers undulate as a consequence of differences in the O-O atom distances in the ordered V(V)O6 and V(IV)O6 octahedra.

Recently, there has been much interest in creating new layered transition metal oxides. Vanadium oxides may be used as sorbents, catalysts, and cathodes in lithium batteries. The modified sol-gel technique allows for some control towards the final structure of the compound. Using this technique, a new layered vanadium oxide phosphate material, containing the surfactant dodecylphosphate, has been synthesized. The compound was analyzed using powder XRD, TGA, SEM, FTIR, TEM, and solid state NMR for both 51V and 31P. V2O3(PO4C12H25)3Na2−xKx(H2O)3.2 is the general formula of the layered product with an interlayer spacing of 36.6 Å The initial compound is composed of a vanadium oxide phosphate layer sandwiched between two hydrocarbon layers. The synthesis, composition, and structure of the initial compound will be discussed. Interestingly, when this compound is calcined to 400°C, the structure changes and is possibly hexagonal. Preliminary results are presented on this calcined material.

The potential energy profile for proton translational motions between two neighboring Alsites in zeolite H-ZSM-5 is calculated by a combined quantum mechanics-interatomic potential function approach. Thepotential energies of the six stable intermediate proton positions and the five transition structures along this path show an almost symmetrical trend reaching the maximum in the middle between these sites. Therefore, the maximum barrier will decrease with decreasing SiO2/Al2O3 ratio of thezeolite. For the SiO2/Al2O3 ratio examined (190) an activation energy of∼ 210 kJ/mol is calculated. This is much lower than the energy of deprotonation, about 1300 kJ/mol. The deprotonation energy of an Al-OH-Si bridge is obviously partially compensated by the proton affinity of the Si-O-Si bridges.

Chemical deintercalation in Fe-substituted lithium nickelate and its effects on the thermal stability and electrochemical behaviour are studied. A sample with Fe:Ni ratio of 1:9 was used as the starting material. Chemical deintercalation of the ceramic product was achieved by acid treatment with 0.6 M aqueous hydrochloric acid solutions at room temperature. The atomic Fe:Ni ratio remained unaffected while the Li:(Fe+Ni) ratio decreased significantly down to ca. 0.5 after acid treatment. Infrared spectroscopy was used to discard a proton exchange side reaction. The initial open circuit voltage (OCV) of non-aqueous electrolyte lithium cells using the chemically deintercalated solids was ca. 3.7 V, while 3.0 V were obtained with the pristine oxide. Heat treating the deintercalated solids lead to oxygen evolution at 230°C with the formation of spinel rock-salt structure solids at 600°C. The improved thermal stability as compared with iron-free lithium nickelate is an interesting factor for battery safety.

For a wide range of technological applications the need for optically transparent, monolithic, mesoporous silicates is readily apparent. Potential areas of utility include filtration, catalysis, and optoelectronics among many others. This laboratory has previously reported on the synthesis of such materials thatare formed through the addition of tetramethoxysilane to a liquid crystal solution of hexanol, cetylpyridinium chloride, and 0.2 M hydrochloric acid, and our investigation into the properties of these materials is a continuing process. We have achieved defect and fracture free material of suitable size (0.5 cm × 3 cm diameter disks) via supercritical drying of the silicate under ethanol or CO2. The dried materials are remarkably similar to ordinary glass in strength, texture, and clarity. They possess pore volumes of ca. 1.0 cm3/g, with BET surface areas >1000 m2/g. We can re-infiltrate thedried monolith with hydroxyethylacrylate, a photo-polymerizable monomer, to create an inorganic/organic nanocomposite. There is fracturing upon re-infiltration, but preliminary tests show that the polymerization proceeds despite the mechanical failure. These findings suggest many possible applications for these unique nanocomposites.

The rhombohedral alkaline earth-bismuth oxide phase, an oxygen ion conductor, does not coexist stably with electronic conductors in any of the three binary systems, Ca-Bi-O, Sr-Bi-O, Ba-Bi-O. A thermodynamically stable composite of a rhombohedral phase that contains Ba and Sr or Ca or both with the electronic conductor BaBiO3 may be synthesized. The rhombohedral phase appears to have complete mutual miscibility of the alkaline earth elements. The composi- tions of rhombohedral phase that coexist with BaBiO3 in the Sr-Ba-Bi ternary system and the Ca- Sr-Ba-Bi quaternary systems are described. The value of ionic conductivity of the rhombohedral phase (at a constant Bi: [Ca+Sr+Ba]) is not dependent on the relative amounts of Ca, Sr, and Ba. The temperature at which the rhombohedral phase undergoes a polymorphic transformation from a low-temperature (2) form that is a weak ion conductor to a high-temperature (β1) form that is a much better oxygen ion conductor. The temperatures of the polymorphic transformation and of the upper stability limit of the rhombohedral phase both depend strongly on Ca: Sr: Ba. The β1 form develops in the Ba-Bi system at the lowest temperatures and at the highest ones in the Ca- Bi system. On the other hand, the Ca-Bi phase has greater thermal stability than its Ba ana- logues. The temperature range over which a useful composite conductor can operate is, there- fore, strongly dependent upon the bulk composition of the system.

Synthesis of Ce0.9Gd0.1O1.95 (CGO) powders from polymeric precursor solutions formed by mixing nitrates and ethylene glycol at 60-85 was investigated with emphasis on the effect of the polymerization of the precursor solution on the crystallization and morphology of the derived intermediate and the resultant oxide powders. It was revealed by FTIR that the molecular structures of the polymeric precursor solution change from aldehyde or ketone groups to carboxylic acid and carboxylate groups with increasing heating time. TG-DTA analyses demonstrated the temperature shifting and the disappearance of the exothermic reactions of the derived powders with different heating times of the polymeric precursor solutions. Furthermore, it was identified by XRD, SEM and TEM that the derived powders can be changed from well crystallized organic formates of Ce1-xGdx(HCOO)3 with dendritic growth to loose agglomerated cubic CGO powders with grain sizes below 10 nm.

The use of isotopically enriched materials on high intensity neutron powder diffractometers allows the derivation of much higher quality structural information than has hitherto been possible. The technique can be applied to materials such as ferroelectrics, superconductors and oxides exhibiting colossal magneto-resistance, where small structural changes associated with phase transitions need to be characterised. Three isotopically pure samples of samarium nickelate have been studied around the metal-insulator transition at 403 K. Simultaneous multi-histogram refinements permit extraction of very high quality structural information that shows smooth variations in bond lengths and angles with all nickel oxygen distances decreasing as the electrons localise.

The NOx decomposition activity of electrochemical cells composed of YSZ solid electrolyte and La1−xCaxMnO3 porous electrodes was examined. La1−xCaxMnO3 powders were prepared by solid-state reaction using corresponding metal oxides and carbonates. The powders were dispersed in polyethylene glycol and screen-printed on both sides of the electrolyte pellet. The electrochemical decomposition of NO was carried out in the temperature range from 973 to 1173 K by passing a mixed gas of 1000 ppm NO and 2% O2 in He through the cell. When the DC voltage was applied to the cell, NO was directly decomposed to N2 and O2 in the oxidizing atmosphere. The cells composed of the La0.8Ca0.2MnO3 electrodes showed a higher NO decomposition ratio and current efficiency than that of other La1−xCaxMnO3 electrodes.

The structures and microstructures of a range of Aurivillius phases have been investigated using transmission electron microscopy. Superlattice reflections arising from rotations of octahedra around the c-axis have been identified and their intensity at room temperature has been shown to diminish as the tolerance factor of the perovskite blocks increases. The paraelectric to ferroelectric phase transition temperature (Tc) has been monitored using permittivity measurements as a function of temperature and Tc has also been shown to decrease as tolerance factor increases. It is proposed that the onset of octahedral tilting and Tc are related in Aurivillius phases.