In an effort to synthesize monophasic superconducting oxides in the quaternary system Bi2O3-SrO-CaO-CuO two studies have been conducted. The melting relations of superconducting oxides Bi2Sr2CaCu2O8 (Bi-2212) and Bi2Sr2Ca2Cu3O10 (Bi-2223) have been experimentally investigated separately at various oxygen fugacities {f(O2)} from I to 3. 10-4 bar at 1 atm total pressure. Several interesting properties of the system have been found with respect to this portion of the quaternary; the modal proportions of liquid produced at the solidus depend on the oxygen fugacity. The amount of liquid produced at the Bi-2212 solidus reached a maximum of approximately 75% at f(O2) = 0.1 bar, Bi-2223's maximum proportion of liquid formed at the solidus continues to increase up to the lowest oxygen fugacity f(O2) = 0.01 bar studied. CaO (with a small amount of dissolved SrO) is the liquidus phase over the entire range of f(O2) for both compositions. (Sr,Ca)2CuO3 is the second phase to crystallize at high f(O2) but, as f(O2) decreases, its primary phase volume shifts for Bi-2212, and Bi2(Ca,Sr)3O6 is the second phase to form. (Sr,Ca)14Cu24O41 exhibited liquidus relationship only in high oxygen fugacities. Only Bi-2212 melts to assemblages that include bismuth-bearing crystalline phases. Bi9(Ca,Sr)16Ox is stable only at high oxygen fugacities and Bi2(Ca,Sr)3O6 is only stable at the lower values. At the lowest oxygen fugacities, Bi-2212 liquids crystallize (SrCa)CuO2 at a higher temperature than (SrCa)2CuO3 and no (Sr,Ca)CuO2 was found in Bi-2223 bulk compositions. These variations apply constraints on the positions of the univariant and invariant phase equilibria and these constraints are described.

Dysprosium doped Bi-based 2212 ceramics were synthesized by a melt-texturing growth process in a 1.2T magnetic field, applied perpendicularly to the main axis of a cylindrically shaped sample. The materials were characterized by X-ray diffraction, optical and scanning electron microscopy and energy dispersive X-ray analyses. The texturing process was optimized with respect to the sample electrical resistivity and AC magnetic susceptibility.

Using a multi-target pulsed laser deposition (PLD) process we synthesized superlattices in the (La0.8Ba0.2CuO2.6±x)m(AECuO2)n system, where AE = Ca or Sr, and m and n were varied. Owing to the sequential deposition process, two-dimensional order is obtained on the perovskite A-sites in the superlattice structures, as evidenced by X-ray diffraction for the materials where AE = Sr. However, when AE = Ca, the films were unstable. Structural units of CaCuO2 could be incorporated into the superlattices by containing them between layers of SrCuO2: (SrCuO2)l(CaCuO2)m(SrCuO2)l(La0.8Ba0.2CuO2.6±x)n. The stability and structural characteristics of particular stacking sequences are discussed with respect to their chemical preferences and are compared to bulk materials of similar stoichiometries, i.e., the (La,AE)CuO3-x system. The latter materials do not exhibit two-dimensional cation-order. Resistance measurements of as-synthesized and post-annealed materials are also discussed.

Electronic properties of the layered compounds with the general composition Ban+1(Pb,Bi)nO3n+1 are quite interesting as the crystal structure of these materials is quite similar to that of high-Tc cuprates. We have investigated the effect of Bi and In substitution on the structure, oxygen stoichiometry (carrier concentration) and the electronic properties of Ba4Pb3O10 compounds. The X-ray powder diffraction results indicate that the unit cell symmetry changes from body-centered tetragonal to cubic with the increasing concentration (x) of Bi and In. The oxygen stoichiometry of the materials is found to increase monotonically with the increase in x(Bi). On the other hand it decreased almost linearly with the increasing x(In). Resistivity of the materials is measured as a function of temperature in the temperature region 3-300K. It is found that the room temeprature resistivity increases with increasing x(Bi/In). Since the oxygen stoichiometry values suggest an increase in the carrier concentration with increasing x(Bi/In), it appears that the disorder caused by the substitution at the Pb site has lead to the carrier localization. For x(Bi)<0.2, we found that the resistivity varies as a function of lnT, which is indicative of weak localization. However, at higher concentrations 3D-VRH behavior is observed. On the other hand the resistivity of indium substituted samples show M-I transition, at low concentrations.

Electrodeposition of multimetallic films at room temperature on metallic substrates followed by oxidation at high temperature (~ 900°C) has often been employed to prepare high temperature superconducting (HTSC) films. A difficulty with this otherwise cheap and simple process is that the degree of surface covering is usually not very high. We have attempted to remediate this problem by sequentially repeating the deposition process on the same film. In this way, we have improved quite markedly critical current density (Jc) of films obtained on Silver substrates.

To quote some figures, Jc at 1 T is ~ 400 A/cm2 after the first deposition/oxidation process and it increases to ~ 2 000 A/cm2 after the fourth one. The evolution of the morphology of the films has been followed by means of scanning electron microscopy (SEM). It shows that, although the degree of surface coverage never attains 100 %, a substantial proportion of the substrate is well coated.

We have also studied the influence of mechanical pressure on the metallic film before the thermal treatment; after the fourth deposition, a pressure of ~15 KBar was applied. In this case a ~ 7% increase in Jc was observed and the density after compression (6.98 g/cm3) attains almost 100 % of the theoretical value for YBa2Cu3O7-δ (Ybacuo).

Solution chemistry has been used to synthesize epitaxial films of SrLaGaO4, SrPrGaO4, SrLaAlO4, and SrPrAlO4 on single crystal substrates of [100] SrTiO3 and [100] LaAlO3. Precursor solutions were prepared from metal methoxyethoxides in 2-methoxyethanol. Films were prepared by spin-casting from partially hydrolyzed solutions followed by firing for 20 minutes in air at 850°C. The structure of the films was determined using X-ray diffraction. Theta/2-theta scans and omega scans (rocking curves) indicated that the films were c-axis aligned. Phi scans proved that the films were also aligned in-plane.

Epitaxial films of lanthanum gallate, praseodymium gallate, and neodymium gallate were prepared on [100] strontium titanate and [100] lanthanum aluminate single crystal substrates using solution techniques. The solutions employed were mixed-metal methoxyethoxides in 2-methoxyethanol. Films were prepared by spin-coating with a partially hydrolyzed solution, followed by firing at 850 °C for 20 minutes in air. Theta/2-theta scans revealed only [h00] reflections and omega scans (rocking curves) indicated good out-of-plane orientation. Pole figures and phi scans revealed good in-plane orientation and a [100] || [100] epitaxial relationship between the film and the substrate.

From an investigation of the structures and electrical properties of compounds in the CsHSO4 - CsH2PO4 system, a simple model is presented for predicting whether or not a solid acid will undergo a structural transition to a disordered, superprotonic phase. Such a transition was measured in ß-Cs3(HSO4)2(H2-x(SxP1-x)O4), α-Cs3(HSO4)2(H2PO4) and Cs2(HSO4)(H2PO4), but not CsH2PO4. It is proposed that entropy drives any solid acid to a high-temperature structure in which the oxygen atoms participate equally in forming hydrogen bonds. If the H:XO4 ratio is not precisely 2:1, such chemical equivalence of oxygen atoms can only be achieved if the structure transforms to a state in which proton occupancies at hydrogen bonds are less than one and/or oxygen site occupancies are less than one. This disorder simultaneously leads to fast proton transport in the high-temperature phase, and thus superprotonic conductivity.

Pyrochlore oxides, A2B2O7, are of interest as fuel cell materials and sensors because, with suitable doping, they may be fast-ion conducting or p- or n-type electronic conductors. An earlier analysis of Y2(ZryTi1-y)2O7 solid solutions showed that substitution of the larger Zr ion for Ti induced progressive disorder in both the cation and anion arrays causing a 103 increase in oxygen ion conductivity. In contrast, Y2(SnyTi1-y)2O7 solid solutions remained essentially fully ordered over their entire range of composition even though the range of average radii of the cation species in the B site overlapped to a considerable degree with those of the (ZryTi1-y) materials. The present work used Rietveld analysis of both neutron and x-ray powder profiles to examine Y2(ZrySn1-y)2O7 compositions along the third leg of the pseudo-ternary system: solid solutions between the stannate, with strong tendency to remain ordered, and the zirconate which has predilection toward complete disorder. Progressive disorder in the oxygen ion array was again observed with increasing y. Mixing between cation sites was found to progress at a rate independent of anion disordering. The behavior was very similar to Y2(ZryTi1-y)2O7, suggesting that the differing behavior of the three systems is due to the ability of Zr to readily enter the eight-coordinated A site.

Porous electrode substrate of La0.7Sr0.2MnO3 was used as the support for the deposition of YSZ thin films. The porosity of the electrode substrate was controlled by sintering temperature and particle size of powders. Thin films of YSZ were fabricated on the electrode by sol-gel method. The YSZ film fabricated by 10-fold coating with 0.05M YSZ sol containing TEA was continuous and crack-free one of 5 mm in thickness. However, hydrogen permeation measurement showed that there was a very small leakage of hydrogen in the fabricated film. In addition to sol-gel method, another technique such as EVD should be employed to make the film completely gas-tight.

Lead, strontium and barium nitrates, like the titanates of the same cations, form a continuous set of solid solutions. 207Pb NMR spectra of mixed crystals of lead/strontium nitrate and lead/barium nitrate each show up to 13 lines, arising from lead ions with from zero to twelve Pb2+ nearest-neighbor cations replaced by Sr2+ or Ba2+. In the case of (Pb,Sr)(NO3)2 these shifted lines are further split by the multiplicity of inequivalent nearest-neighbor replacements. The average shift per Sr2+ ion is 21.8 ppm; that for Ba2+ is smaller. Using Monte Carlo/Metropolis calculations, the intensities of the resonances can be fit to statistical models of Pb2+ and Sr2+ ion distributions, and used to probe the microenergetics of solid solution formation. The data can be satisfactorily fit by distributions in which the cations are slightly clustered, with like pairs of nearest neighbors being favored by 120 J/mol over unlike pairs. Interestingly, this finding is inconsistent with the conventional interpretation of powder diffraction results for the mixed crystals, where the dependence of lattice parameter on composition shows a slight positive curvature, generally held to indicate a favorable interaction between unlike ions.

SrFeCo0.5Oy has been identified as a potential dense ceramic membrane material used for gas separation at elevated temperatures. Neutrons play an important role in the study of such materials, particularly due to the favorable scattering lengths of Fe, Co and O. In-situ neutron diffraction experiments allow these materials to be studied under a wide range of temperatures and oxygen partial pressures. Results indicate very complex behavior of individual phases during synthesis and under operational membrane conditions.

The synthesis of thin film of nickel oxide is important due to their potential application in eletrochromic displays which can be used in optical displays and as windows controlling the light intensity. Dip coating through sol-gel method is a possible low energy method of coating. Hence this method of film growth has been chosen under various concentration of water, catalyst (acetic acid) and precursor. The films were characterized by XRD, FTIR, thickness profiler and SEM. The films which were synthesized with the concentration of Ni=0.005 molar were found to have low positive current density while the coloration was getting dark when concentration of Ni was increased to 0.015 molar. Increase in concentration of acetic acid decreases the positive current density. Small-Angle X-ray Scattering (SAXS) and density measurements were carried out for the structural characterization of the xerogels. A denser material was obtained at high concentration of acetic acid. The physical and chemical properties of the films and xerogels are well correlated with the electrochemical properties of the films.

The correlation between 23Na and 31P nuclei in alkali phosphates has been investigated by cross-polarization MAS NMR spectroscopy. Connectivity between sodium ions with various phosphorus tetrahedra has been demonstrated in a variety of crystalline-and amorphous alkali phosphates. CPMAS NMR experiments were also performed on sodium aluminophosphate glasses from both quadrupolar nuclei (23Na and 27Al) to the phosphorus nuclei to establish connectivity of sodium and phosphorus as well as aluminum and phosphorus nuclei in these systems.

Most liquid crystals are made of organic molecules, very few of them are based on mineral compounds. Vanadium pentoxide gels and sols have been shown to give mesophases. They are made of ribbon-like polymeric particles of vanadium pentoxide dispersed in water. Ansitropic xerogel layers are formed when these gels are deposited and dried onto flat substrates. Dehydration is reversible and fluid phases are again obtained via a swelling process when water is added to the xerogel.

When observed by polarized light microscopy, colloidal suspensions of V2O5 ribbons display defects typical of lyotropic nematic phases. Dilute nematic suspensions can even be oriented by applying a magnetic field of about 0.5 Tesla. Such a liquid crystal behavior is mainly due to the highly anisotropic shape of vanadium oxide colloidal particles. Acid dissociation at the oxide/water interface gives rise to surface electrical charges and electrostatic repulsions should also be responsible for the stabilization of the nematic phase.

Superionic MSnF4 are the highest performance fluoride ion conductors, with PbSnF4 being the best. Prototypes of devices using PbSnF4 have been constructed and tested. Since the fluoride ion mobility is thermally activated, some devices might be used more efficiently above ambient temperature. Therefore, it is of prime importance that the stability of these materials be tested under potential conditions of use, since thermal degradation and phase transitions are likely to alter the conducting properties. Tetragonal SrSnF4, α-PbSnF4 and BaSnF4, and orthorhombic o-PbSnF4, are stable at ambient conditions, even in air. However, all undergo significant deterioration when heated in air: the color changes from white to yellowish, and tin hydrolysis and oxidation takes place. They are much more stable under inert conditions (nitrogen or argon). However, PbSnF4 undergoes several phase transitions at high temperatures: o to α starting at ca. 100°C, α to β (reversible, but the reverse reaction is very sluggish) starting at 250°C, β to γ (reversible) at 390°C. β-PbSnF4 can be quenched to ambient temperature and is metastable for long times, however, eventually it starts changing to stable α-PbSnF4 and this change is uncontrollable and is faster above ambient temperature. Microcrystalline μγ-PbSnF4, obtained by ball milling any other phase of PbSnF4, gives rapidly a-PbSnF4 at 200°C. In addition, for all MSnF4, hydrolysis of the Sn-F bonds to Sn-O occurs with traces of moisture.

The fluorite type MF2 materials react at high temperature with tin(II) fluoride SnF2 in the 1: 1 stoichiometry to give high performance fluoride ion conductors MSnF4. However, the reaction takes place only for the largest M cations (M = Sr, Pb and Ba). For the others (M = Cd and Ca), no reaction takes place. Furthermore, when the reaction occurs, it is observed that the reactivity of SnF2 with MF2 is highly dependent on M. The reaction with PbF2 is the easiest; it is complete at 250°C, whereas 500°C is required with SrF2 and BaF2. In addition, with SrF2, an incomplete reaction is observed very often. Moreover, PbF2 and SnF2 fully react at other stoichiometries to give other materials, whereas SrF2 and BaF2 do not, and with CdF2 and CaF2 not even MSnF4 is formed. A structural analysis based on bond angles and using the size of the M2+ cations is used in an attempt to explain the lack of reactivity for the smallest M2+ cations and the poor reactivity of SrF2. However, the relative cationic sizes cannot explain all the trends, inclusing the exceptionally high reactivity of PbF2 (lower reaction temperature, much richer source of materials). An explanation based on the electronic structure of tin(II) and lead(II) has been developped in order to account for the results.

The hydrothermal syntheses and structures of a new series of organically templated UIV materials are presented. The materials, UFO-5 (C5NH14)2(H3O)U2F13, UFO-6 (C5N2H14)2U2F12H2O and UFO-7 (C5N2H14)(H3O)U2F11, exhibit unprecedented topologies as well as represent 0-D (UFO-5), 1-D (UFO-6), and 2-D (UFO-7) phases. By systematic experimentation and utilizing a composition prism, wherein the reagents including H20 are graphically depicted. we have determined stability regions in which UFO-5, 6, and 7 can be synthesized as phase pure products. In addition, through pH measurements we observe a direct relationship between the acidity of the reaction and the dimensionality of the product. We suggest that the increased acidity facilitates condensation of the molecular uranium units in UFO-5. to produce the 1-D UFO-6 and at higher acidity the 2-D UFO-7.

Structural analogies have been demonstrated between the β-cristobalite, α-quartz and moganite phases of PON and its isoelectronic analog SiO2. Whereas the energetics of silica are well established, no data exist for the energetics of formation of nitridophosphates. High temperature solution calorimetry was used to determine the energetics of PON samples and a series of “LiNaPON oxynitride” glasses. Enthalpies of formation were measured as -371.71 ± 4.45 kJ/mol and -356.14 ± 3.98 for β-cristobalite and amorphous PON respectively and as -961.88 ± 3.86 kJ/mol for a 9 wt% nitrogen containing LiNaPON glass. These values constitute the first set of energetics data necessary to achieve further thermodynamic studies on nitridophosphates.

By using both alumina addition and nitrogen/oxygen substitution within PO4 tetrahedra, it is possible to prepare durable phosphate glasses without affecting their specific properties such as low melting temperatures and high thermal expansion coefficients. In particular, “LiKMgAlPON” nitrogen-rich glass compositions have a chemical durability on the same order as soda lime window glass, associated with a glass processing temperature as low as 800°C.