The synthesis, structure and magnetic properties of monoclinic Nb12O29 are described. The synthesis of a pure bulk sample is difficult due to the large number of other similar phases. It is achieved by rapid reduction of H-Nb2O5 with Nb metal. The compound is shown to undergo a charge ordering transition at low temperature which provokes long range magnetic order in an intriguing one dimensional arrangement.

Silicon carbide nanotubes have been prepared and decorated with CoFe2O4 spinel. These nanocomposites were prepared by incipient wetness impregnation of the dried SiC support with a stoichiometric aqueous solution of the cobalt and iron nitrates. After drying, subsequent annealing treatments were performed under air in the temperature range 873 to 1073 K. X-ray diffraction and high resolution transmission electron microscopy reveal the presence of spinel nanoparticles at the surface of the tubes. Magnetic properties of the nanocomposites show in the magnetic field explored (up to 5 T) that saturation magnetization is not observed neither at room temperature nor at 5Kelvin. The nanometric character and the nature of the spinel particles are also confirmed by the coercive field (1.6 T) observed at low temperature and the curie temperature.

During the past decades the solid state chemistry of tellurium oxides has been enriched by a series of quaternary metallates. Interest attaches not only to the chemical and physical properties of these compounds, but also to their structure, which have been studied by modern methods. The partial similarity of earth alkaline metals and lead in solid state chemistry and their relationships in oxides opens a wide field of investigations. Eight new compounds in the systems Ba-M-Te-O (M= Nb, Ta) and Pb-M-Te-O (M = Mn, Ni, Cu, Zn) were prepared and structurally characterized: Ba2Nb2TeO10, Ba2M6Te2O21 (M = Nb, Ta) and the lead compounds PbMnTeO3, Pb3Ni4.5Te2.5O15, PbCu3TeO7, PbZn4SiTeO10 and the mixed compound PbMn2Ni6Te3O18. The structures of all compounds are based on frameworks of edge and corner sharing oxygen octahedra of the transition metal and the tellurium. Various different channel structures were observed and distinguished. The compounds were prepared by heating from mixtures of the oxides, and the single crystals were grown by flux method or solid state reactions on air. The synthesis conditions were modified to obtained microcrystalline material for purification and structural characterizations, which were carried out using a variety of tools including powder diffraction data and refinements of X-ray data. Relationships between lead transition metal tellurium oxides and the earth alkaline transition metals tellurium oxides are compared.

The isostructural oxides LaTiO3.5, SrNbO3.5 and CaNbO3.5 adopt layered structures made up of perovskite related slabs intermitted by layers of non-linking BO6-octahedra (B=Ti, Nb). In these phases the transition metals Ti and Nb are in their highest oxidation states +IV and +V, respectively. They are insulators, in the case of the Ti phase a ferroelectric insulator with the highest known Tc (above 1700°C). By changing the oxygen stoichiometry, i.e. by controlled reduction or re-oxidation processes in the range of 2ABO3.5 ø 2ABO3 + ½ O2 (A=La or Sr, B=Ti or Nb) mixed valence phases are obtained. Accordingly, the physical properties of the different phases alter from insulating to semiconducting or to conducting. Detailed studies on the structural changes reveal, however, that the sublattice of the metal cations is basically conserved. In principle the reduction corresponds to a condensation of the perovskite layers leading to intermediate phases such as the semiconducting LaTiO3.4, in which five TiO6-octahedra thick perovskite slabs constitute the structural framework and 20% of the Ti+IV cations are reduced to Ti+III. Conductivity measurements using single crystals of the corresponding Ti and Nb phases reveal that these mixed valence oxides must be considered as one-dimensional conductors. The fully reduced phases La+IIITi+IIIO3 and Sr+IINb+IVO3 adopt distorted perovskite structures. Extensive high resolution electron microscopic and light microscopic investigations have been carried out in order to characterize the structural mechanism of the reversible, highly topotactic reduction and re-oxidation processes. Thermogravimetric measurements in reducing and oxidizing atmospheres have been performed for the identification of the temperature ranges wherein the decisive mass changes take place. The results of the described experiments support that the properties of such metal oxides can be finely and reversibly tuned by merely changing the oxygen stoichiometries.

The gallium diphosphonate, Ga2[O3PC2H4PO3](H2O)2F2·H2O, has been prepared under solvothermal conditions from a HF/ pyridine solvent system. The structure of the material was determined by Rietveld refinement using the isostructural aluminium compound as the starting model for refinement. The structure consists of chains of corner sharing GaO4F2 octahedra with bridging F atoms linking the octahedra. The chains of octahedra are linked together in two directions perpendicular to the chain direction by the ethylenediphosphonate groups. The resulting structure contains a one-dimensional channel system in which extra-framework water molecules reside. Thermal gravimetric analysis of the material shows that 40 % of the extra- framework water can be reversibly absorbed. Thermodiffraction studies show that the material retains its structural integrity until all the extra-framework water is lost and then undergoes a considerable loss in crystallinity as the framework water molecules are lost. The crystallinity of the material then progressively decreases as the temperature is increased.

Acceptor and Donor codoped BaTiO3 and Ba1−xSrxTiO3 are prepared. For Ba1−xLaxTi1−xFexO3,BaTiO3 remains as tetragonal phase up to about 5mol% LaFeO3. For x ≥0.06, the structure changes to cubic at room temperature. The phase change shifts the Curie temperature to lower value and increases the tunability at room temperature. Doping of other acceptor (Al, Cr) and donor (Sm, Gd, Dy) ions has the same effect although with varying levels of tuning. BaTiO3: 4%LaFeO3 has the highest tunability among the studied systems, which is even higher than Ba0.6Sr0.4TiO3. Co-doping of (La, Fe) and (La, Al) in Ba1−xSrxTiO3 also lowers the Curie temperature and increases the tunability of high Ba content samples at cryogenic temperature.

The effective valence, zFe–αFe*, of mobile Fe-ions (Fe2+, Fe3+) in semiconducting Fe3O4 was determined at elevated temperatures via the electrotransport experiment in association with the literature data on the cation diffusivity and total electrical conductivity. It has been found that the value for zFe–αFe* varies systematically from below 2 up to 3 with oxygen partial pressure at a fixed temperature. The effective valence is determined not only by the mobility difference of Fe2+ and Fe3+ ions (zFe), but also by the cross effect between the cations and electrons upon their transfer (αFe*). A value of zFe–αFe* between 2 and 3 may be attributed to the mobility difference between Fe2+ and Fe3+ ions even in the absence of the cross effect, but the values of zFe–αFe* < 2 clearly indicate that the cross effect is in play in Fe3O4.

Study of the microstructure of electronic materials can be enhanced by using high resolution transmission electron microscopy (TEM) combined with the technique of digitized image analysis. We show here a practical image analysis method for the microstructures of acceptor graphite intercalation compounds (GICs) with CuCl2 and FeCl3 intercalates. The two dimensional fast Fourier transform (2D-FFT) was used for the frequency analysis of the TEM pictures. It is found that the lattice images of CuCl2-GICs consist of different frequency images corresponding to specific frequencies. The detailed features of the stage-1 structure of the FeCl3-GICs is extracted quantitatively by this method from a relatively indistinct TEM picture. The stage structure of the CuCl2- and FeCl3-GICs are further investigated by analyzing the reconstruction of the TEM images by means of the two dimensional inverse FFT (2D-IFFT).

In a good semiconductor the electrons (or holes) propagate through the lattice structure of well ordered atoms without being scattered by the coherent vibrations of the crystal. Thus semiconductors are good conductors of electrons (or holes) and as such have given rise to modern microprocessors that are revolutionizing the way we live. In the same semiconductors the vibrations of the lattice atoms mainly carry the heat. Due to the covalent nature of the bonding in these materials the thermal conductivity is very large. These are therefore poor materials for thermoelectric applications. If the atomic vibrations, or phonons, can be localized so that the heat transfer is essentially an atom-to- atom propagation, then the thermal conduction can be drastically reduced. A semiconductor can, in principle, have the thermal conductivity of a glass. Amorphous semiconductors are of course very poor conductors of electricity therefore one does not want the electrons to propagate through a glass-like material. Instead one wants the electrons to travel as though they only “see” the well-ordered, periodic structure of a crystal while the phonons are scattered by localized disorder within the covalently bonded lattice. “Open structure” semiconductors do, in fact, exist and recent research has given rise to new thermoelectric materials.

In this study we investigated the evolution of nickel hydroxide, which acts at the positive electrode of the Ni/Cd, Ni/MH and Ni/H2 alkaline batteries. We found that the addition of bismuth oxide in the course of the active material preparation prevents the dissolution-re-crystallization processes of the nickel hydroxide that are harmful to the electrode efficiency. From XRD and SEM studies, it is shown that treatment of the bismuth doped-nickel hydroxide by hydrogen in 5 N KOH electrolyte prevents metallic nickel formation. Moreover, it appears to stabilize the α-type nickel hydroxide structure, preventing its transformation into the β-Ni(OH)2 phase. Finally, an implementation of these findings towards the most efficient use of nickel positive electrodes is shown.

YAG powders and coatings were developed for the first time by a novel precursor plasma spraying technique using the radio frequency (RF) induction plasma technique. The XRD of the as -sprayed coating confirms the presence of YAG, H-YAP or O-YAP or a mixture of the above depending on the spray conditions. 27Al MAS NMR of the YAG coating corroborates the x-ray results. TEM studies on the coatings confirm that the coating consists of nano-structured particles. The successful spraying of these complex oxide coatings proves that chemistry of phase formation can be controlled in the plasma, thus opening up new avenues in material synthesis.

Li2NaCu2O4 has been prepared by solid state reaction under high-pressure (250 Atm) oxygen. A structural study, using time-of-flight powder neutron diffraction on a sample made with 7Li, shows a material isostructural with Li3Cu2O4, with sodium occupying the octahedral and lithium the tetrahedral A-cation sites. A 7Li MAS-NMR study of Li3Cu2O4, Li2NaCu2O4 and Li2CuO2 has been used to confirm the Li/Na site ordering.

Recently, a renewed research interest has emerged for the development of visible light, down-converting phosphors for application in white light emitting diodes (LEDs). In such devices, a blue GaN LED can act as the primary light source, exciting photoluminescence in a phosphor with subsequent broad-band emission occurring at lower energies. It was recently reported that use of a combinatorial approach to synthesize and screen potential inorganic phosphors for such an application could aid in identifying improved phosphors for blue to yellow down conversion. Using solution chemistry techniques developed by Symyx Technologies, solid state thin-film arrays (libraries) based on the garnet structure (A1-xBx)3(C1-yDy)5O12:Ce3+, where x and y = 0 to 1.0 and A, B = Y, Gd, or Lu; C., D = Al or Ga, were synthesized. X-ray diffraction was used to select library samples of the crystalline garnet phase. Libraries of these various garnets were then characterized, and their spectral properties compared to traditionally prepared bulk powder phosphors of similar composition. Emission and excitation trends show that as larger cations are substituted for Y (A = Y), emission and excitation are red-shifted and as larger cations are substituted for Al (C = Al), emission and excitation are blue-shifted. If smaller cations are substituted for Y and Al, an opposite trend is observed.

A pure form of the compound [(CH3)4N]0.2Mn0.06V2O5+δ•0.2H2O has been synthesized by the hydrothermal technique. A manganese richer compound, [(CH3)4N]0.18Mn0.1V2O5+δ•0.35H2O, has also been synthesized. By comparison to [(CH3)4N]0.17Fe0.1V2O5+δ•0.17H2O, the structure of these compounds consists of double sheets of vanadium oxide with tetramethyl ammonium ions in the interlayer spaces. Both compounds display reversible lithium intercalation with sharp end points. The lithiation capacity is lowered by the increase in manganese content.

The synthesis temperature for silicalite-I (MFI) can be raised to 300°C by applying high pressure to stabilize the structure-directing organic template. The elevated temperature and pressure favor theformation of crystals with improved quality. Prismatic silicalite-I crystals with a uniform size of about 0.7× 0.2 × 0.2 mm have been obtained by heating a gel prepared from TMA-silicate solution, TPABr andsodium hexafluorosilicate at 250°C under a pressure of 80 MPa. The influence of synthesis conditions on the crystal sizes has been studied by systematically changing temperature, pressure and gel compositions. Underthe specific conditions of 250°C and 80 MPa, a strong correlation was found between the crystal size andthe F/Si mole ratio of the starting gel, which enables the preparation of uniform crystals of silicalite-I with preset dimensions.

A microstructural change during the formation reaction of aluminum titanate from a mixture of rutile and corundum powders has been studied. The characterization was carried out using a polarization microscope, a scanning electron microscope and a micro-focus X-ray diffractometer. The formation of aluminum titanate was controlled by a nucleation step. The formation reaction proceeded to form spherically oriented regions of aluminum titanate grains among the matrix of rutile and corundum. At the end of the reaction, the specimen was entirely filled with the oriented region of consisting several hundred micrometers. The oriented region was composed of primary aluminum titanate grains of several micrometers and pores. Large cracks due to a thermal expansion anisotropy were formed at the boundaries of the orientated regions. The formation of the oriented region was caused by a small change in free energy, increasing elastic energy, and the endothermic nature of the reaction.

The electrical measurement has demonstrated that conductivity of CaO-doped CeO2 has higher activation energy for low temperature and lower activation energy for high temperature. A model with two different kinds of defect interactions between oxygen vacancy and doped cations has been used to interpret the phenomenon. Diffusion based on hopping of oxygen ions was assumed as the mechanism of electrical conduction. The analysis indicated that at high temperature free oxygen vacancies are dominant and the activation energy is only for oxygen ion hopping. At low temperature, however, oxygen vacancies associated with dopant calcium ions are dominant for high CaO content and the activation energy is the energy for hopping of an oxygen ion plus half of the association energy between one oxygen vacancy and one calcium ion. For low level doping, both free and associated oxygen vacancies are important.

Hydrothermal reactions of rare-earth metal acetates and nitrates with oxalic acid (H2C2O4) and 3,5-pyridinedicarboxylic acid (H2pddc) in triethylamine/water solutions have yielded five isostructural polymers with the general formula: [Ln(pddc)(C2O4)1/2(H2O)2]·H2O. [Ln = La(1), Pr(2), Nd(3), Eu(4) and Er(5)]. These compounds crystallize in monoclinic crystal system, space group P21/n, Z = 4, with only slight variations in their unit cell parameters: 1 a = 7.747(2), b = 9.954(2), c = 15.134(3) Å, = 98.64(3)°, V = 1153.8(4) Å3; 2 a = 7.707(2), b = 9.895(2), c = 15.006(3) Å, β = 98.54(3)°, V = 1131.7(4) Å3; 3 a = 7.688(2), b = 9.897(2), c = 14.955(3) Å, β = 98.43(3)°, V = 112 5.6(4) Å3; 4 a = 7.638(2), b = 9.842(2), c = 14.809(3) Å, β = 98.42(3)°, V = 1101.2(4) Å3; 5 a = 7.573(2), b = 9.761(2) Å, c = 14.630(3) Å, β = 98.10(3)°, V = 1070.7(4) Å3. The structure of these compounds is composed of 2D Ln(pddc) layers that are interconnected by chelating oxalate. Within the layer, each rare-earth metal forms a monodentate bond with each of the four pddc groups. The metal centers in the neighboring layers are bridged through µ4-oxalate, resulting in a three-dimensional framework. The remaining two sites around the eight-coordinate Ln are occupied by water molecules. Compounds 2, 3, and 5 exhibit paramagnetic behavior and 1 is diamagnetic. They are thermally stable up to 250°C.

The hydrothermal reactions of Cu(NO3)2.3H2O, K2CrO4 and exo-bidentate ligand bpy/bpe, (bpy = 4,4'-bipyridine, bpe = trans-1,2-bis(4-pyridyl)ethylene) result in two pillared 3D organic-inorganic hybrid compounds. Both contain bimetallic layers of copper(II) cations and chromate anions, which are directly connected by different organic ligands, leading to pillared structures with varying pillar length and thickness of layers. Crystal data for [Cu3(CrO4)2(OH)2(bpy)2] (1): triclinic, P1, a = 5.358(1), b = 5.603(1), c = 13.515(3) Å, α = 81.78(3), γ = 86.56(3), Å3 = 79.75(3)°, V = 394.91(13) Å3, Z = 1; [CuCrO4(bpe)] (2): monoclinic, C2/c, a = 23.282(5), b = 11.917(2), c = 9.726(2) Å, β = 112.99(3)°, V = 2484.2(8) Å3, Z = 8.

Single crystals of Ba8CoRh6O21 were grown out of a potassium carbonate flux. The structure was solved by a general method using the superspace group approach. The superspace group employed was R3m(00γ)0s with a = 10.0431(1) Å, c1 = 2.5946(1) Å and c2 = 4.5405(1) Å, V = 226.60(1) Å3. Ba8CoRh6O21 represents the first example of an m = 5, n = 3 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite related oxides and contains chains consisting of six consecutive RhO6 octahedra followed by one distorted CoO6 trigonal prism. These chains in turn are separated from each other by [Ba]∞ chains.