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Crystalline BaTiO3 powders were precipitated by reacting fine TiO2 particles with a strongly alkaline solution of Ba(OH)2 under hydrothermal conditions at 80°C to 240°C. The characteristics of the powders were investigated by X-ray diffraction, transmission electron microscopy, thermal analysis and atomic emission spectroscopy. For a fixed reaction time of 24 hours, the average particle size of BaTiO3 increased from ∼50 nm at 90°C to ∼100 nm at 240°C. At synthesis temperatures below ∼150°C, the BaTiO3 particles had a narrow size distribution and were predominantly cubic in structure. Higher synthesis temperatures produced a mixture of the cubic and tetragonal phases in which the concentration of the tetragonal phase increased with increasing temperature. A bimodal distribution of sizes developed for long reaction times (96 h) at the highest synthesis temperature (240°C). Thermal analysis revealed little weight loss on heating the powders to temperatures up to 700°C. The influence of particle size and processing-related hydroxyl defects on the crystal structure of the BaTiO3 powder is discussed.

Thin films of thallic oxide Tl2O3 (Ia3, a=1.0534 nm) were electrodeposited on the three low-index surfaces of single crystal Au (Fm3m, a=0.4079 nm). Epitaxial films of Tl2O3 with a strong out-of-plane (100) texture were obtained in the case of the (100) and (111) Au substrates, while the film on the (110) Au substrate did not show a preferred out-of-plane orientation. Studies of the in-plane orientation of the films revealed that the large lattice mismatch between Au and Tl2O3 is accommodated by the formation of the coincidence lattices on (100) and (111) Au.

Nanocrystalline films of δ-Bi 2 O 3 were electrodeposited at 65°C directly from alkaline solutions of tartrate-complexed Bi(III). This face-centered-cubic polymorph of Bi 2 O 3 is normally only stable at high temperatures (729–825°C). The material has the highest known oxide ion mobility. We propose that the high temperature form of the oxide is stabilized due to the nanocrystalline (70 nm) size of the particles in the film. The oxide also deposits epitaxially onto a single-crystal Au(110) substrate with strong in-plane and out-of-plane orientation. The large lattice mismatch (35.4%) is accommodated by forming a coincidence lattice, in which the δ-Bi 2 O 3 is rotated 90° relative to the Au (110) substrate. The epitaxial relationship between film and substrate may also serve to stabilize the high-temperature structure.

Single-crystal films are essential for devices because the intrinsic properties of the material, rather than its grain boundaries, can be exploited. Cubic bismuth oxide has the highest known oxide ion mobility, which makes it useful for fuel cells and sensors, but it is normally only stable from 729° to 825°C. The material has not been previously observed at room temperature. Single-crystal films of the high-temperature cubic polymorph of bismuth oxide were epitaxially electrodeposited from an aqueous solution onto single-crystal gold substrates. The 35.4 percent lattice mismatch was accommodated by forming coincidence lattices in which the bismuth oxide film was rotated in relation to the gold substrate. These results provide a method for producing other nonequilibrium phases that cannot be accessed by traditional thermal processing.

Application of a constant cathodic current to an electrode in an alkaline Cu(II) lactate solution results in oscillation of the electrode potential during the electrodeposition of copper/cuprous oxide layered nanostructures. The electrochemical quartz crystal microbalance (EQCM) is used for in situ phase analysis measurements of the nanoscale layers and the results are compared with bulk XRD measurements. The EQCM is also used to estimate the layer thicknesses and overall modulation wavelength of the nanostructures. We propose that Cu2O is deposited during the positive spikes in electrode potential, while a composite of Cu and Cu2O is deposited during the more negative plateau region of the oscillation. The modulation wavelength calculated from the EQCM is in good agreement with that observed with scanning electron microscopy. The EQCM is shown to be a useful tool for estimating layer thicknesses and phase compositions for layers that are too thin to be examined by other instrumental techniques.

Layered nanostructures of copper metal and cuprous oxide are electrodeposited from alkaline solutions of Cu(II) lactate at room temperature. No subsequent heat treatment is necessary to effect crystallization. The electrode potential spontaneously oscillates during constant-current deposition. At a fixed current density the oscillation period decreases as either the pH or temperature is increased. The oscillations are periodic in stirred solution, but show period doubling and evidence of quasi-periodic or chaotic behavior in unstirred solution. The phase composition and resistivity of the films can be controlled by varying the applied current density. The resistivity of the films can be varied over ten orders of magnitude. Scanning electron microscopy shows that the films are layered.

The structures and valence states of iron ions in several iron phosphate glasses with batch compositions similar to 40Fe2O3-60P2O5 (mol%) have been investigated using Mossbauer spectroscopy, X-ray absorption fine-structure spectroscopy (XAFS), X-ray photoelectron spectroscopy (XPS), differential thermal (DTA) and thermo-gravimetric (TGA) analysis and X-ray and neutron diffraction. Mossbauer spectra show that a redox equilibria corresponding to an Fe(II)/[Fe(II) + Fe(III)] ratio of 0.2–0.4 is reached under processing conditions described in this paper. Even though the valence state of iron ions in the glass appears to be insensitive to the oxygen content in the melting atmosphere, the Fe(II) content can be increased within the observed range of redox equilibria by increasing the partial pressure of a reducing gas in the melting atmosphere. Large amounts of Fe(II), Fe(II)/[Fe(II) + Fe(III)] ≥ 0.4, appear to be detrimental to the glass-forming ability of the iron phosphate melts. The local structure of the iron phosphate glasses appears to be related to the short range structure of crystalline Fe3(P2O7)2 which consists of a network of (Fe3O12)−16 clusters. These clusters consist of one iron(II) ion and two iron(III) ions in sixfold coordination with near-neighbor oxygen ions. The (Fe3O12)−16 clusters are interconnected via (P2O7)−4 groups. Compared to other phosphate glasses, the proposed structure for iron phosphate glasses contain a smaller number of POP bonds, a feature which is believed to be responsible for the unusually good chemical durability of iron phosphate glasses.

Superlattices in the Pb−Tl−O system were electrodeposited at room temperature from aqueous solution. The deposition solution was 0.005 M Tl(I) and 0.100 M Pb(II) in 5 M NaOH. The superlattices grew...

AgO has been studied extensively for its use as the cathode material in zinc-silver oxide batteries. Continuous films of silver(II) oxide (AgO) have been electrodeposited directly from aqueous solutions of 50 mM silver acetate/25 mM sodium acetate onto 430 stainless steel, polycrystalline platinum, and indium-tin oxide-coated glass. Current efficiencies for the electrodeposition process ranged from 62 to 95% and were a function of the applied current density. X-ray diffraction of the electrodeposited films reveals a [010] texture when the thickness is greater than 1 {micro}m. Freshly ground films or powders exhibit only reflections consistent with the monoclinic AgO structure. Rietveld analysis confirms the ground films are single-phase AgO with a P 2{sub 1}/c space group. The films were imaged and film thickness was measured by atomic force microscopy. Thermogravimetric analysis shows that the films begin to decompose in air above 130 C, with an abrupt weight loss between 180 and 200 C. The total weight loss of 6.4 to 6.5% corresponds to thermal decomposition of AgO to Ag{sub 2}O with loss of oxygen. A direct optical bandgap of 1.1 eV was measured. The black AgO films absorb strongly in the near infrared and throughout the visible region. The four-point resistivitymore » of the AgO films was 12 {+-} 1 {Omega} cm.« less

Lanthanum chromate (LaCrO4) was synthesized as a low temperature ( < 700 °C) intermediate to perovskite-type, lanthanum chromite (LaCrO3). The lattice parameters, atom positions and bond lengths determined from X-ray powder diffraction show that LaCrO4 forms a monazite-type crystal structure. Lanthanum chromate forms a solid solution with Ca, having a solubility between 10 and 20 at%. Thermal analysis shows that at ambient oxygen pressure, LaCrO4 transforms to LaCrO3 at a temperature near 700 °C. It also indicates that (La,Ca)CrO4 initially transforms to LaCrO3 and CaCrO4 with the subsequent formation of a (La,Ca)CrO3 solid solution. Evidence of Ca segregation to the surface of (La,Ca) CrO3 particles is given by Auger electron spectroscopy and scanning electron microscopy.[/p]

We have examined the consequences of assuming the existence of a light scalar boson, weakly coupled to neutrinos, and not coupled to any other light fermions. For a range of parameters, we find that this hypothesis leads to the development of neutrino clusters which form in the early Universe and which provide gravitational fluctuations on scales small compared to a parsec (i.e., the scale of solar systems). Under some conditions, this can produce anomalous gravitational acceleration within solar systems and lead to a vanishing of neutrino mass-squared differences, giving rise to strong neutrino oscillation effects.

Nanometer-scale layered structures based on thallium(III) oxide were electrodeposited in a beaker at room temperature by pulsing the applied potential during deposition. The conducting metal oxide samples were superlattices, with layers as thin as 6.7 nanometers. The defect chemistry was a function of the applied overpotential: High overpotentials favored oxygen vacancies, whereas low overpotentials favored cation interstitials. The transition from one defect chemistry to another in this nonequilibrium process occurred in the same potential range (100 to 120 millivolts) in which the rate of the back electron transfer reaction became significant. The epitaxial structures have the high carrier density and low electronic dimensionality of high transition temperature superconductors.

AgO has been studied extensively for its use as the cathode material in zinc-silver oxide batteries. Continuous films of silver(II) oxide (AgO) have been electrodeposited directly from aqueous solutions of 50 mM silver acetate/25 mM sodium acetate onto 430 stainless steel, polycrystalline platinum, and indium-tin oxide-coated glass. Current efficiencies for the electrodeposition process ranged from 62 to 95% and were a function of the applied current density. X-ray diffraction of the electrodeposited films reveals a [010] texture when the thickness is greater than 1 {micro}m. Freshly ground films or powders exhibit only reflections consistent with the monoclinic AgO structure. Rietveld analysis confirms the ground films are single-phase AgO with a P 2{sub 1}/c space group. The films were imaged and film thickness was measured by atomic force microscopy. Thermogravimetric analysis shows that the films begin to decompose in air above 130 C, with an abrupt weight loss between 180 and 200 C. The total weight loss of 6.4 to 6.5% corresponds to thermal decomposition of AgO to Ag{sub 2}O with loss of oxygen. A direct optical bandgap of 1.1 eV was measured. The black AgO films absorb strongly in the near infrared and throughout the visible region. The four-point resistivitymore » of the AgO films was 12 {+-} 1 {Omega} cm.« less

Schematic of the Cu2O/PbS semiconductor heterojunction on Au (100) showing the epitaxial relations between the layers. The 0.5-μm-thick PbS and Cu2O films were consecutively electrodeposited onto a Au(100) single crystal at room temperature. Both layers showed a strong (100) out-of-plane texture. Azimuthal X-ray diffraction studies of the in-plane relationships revealed that the PbS structure is rotated 45° relative to the substrate, while the Cu2O overlayer shows no rotation with respect to Au.

Epitaxial films of Fe3O4(111) are electrodeposited on single-crystal Ni(111). The lattice mismatch reduces from +138% in the ⟨011⟩ directions to −0.7% by forming a coincidence lattice in which 5 unit meshes of O overlap with 12 unit meshes of Ni.

Small lattice mismatches and gas-phase deposition are typically used for growing epitaxial films on single-crystal substrates. A 1-µm thick film of PbS can be epitaxially electrodeposited onto a Au (100) single crystal. The large lattice mismatch (45.5 %) between Au and PbS is accommodated by the formation of a coincidence lattice, in which the epitaxial film is rotated by 45 degrees relative to the substrate. The coincidence lattice reduces the mismatch to +2.9 %.

The structural and electrical properties of SrCe1-xYbxO3 ceramics have been studied as a function of temperature and Yb-concentration using x-ray diffraction and impedance techniques. The influence of Yb-dopants on electrical transport and structural disorder has been studied. A correlation between the structural properties, electrical conductivity is observed and discussed. These measurements allow us to determine the mechanism of charge carrier compensation and also the concentration and mobility of the electrical species.

Nanocomposite films of copper metal and cuprous oxide were electrodeposited at room temperature from an alkaline copper(11) lactate solution. The electrode potential oscillated spontaneously during constant-current deposition of the composites. The oscillations were periodic in a stirred solution, but became chaotic in unstirred solution. For a given current density the phase composition was a strong function of solution pH. As the pH was increased, the cuprous oxide content increased. At pH 12, no oscillations were observed, and pure cuprous oxide was deposited. At pH 9, the phase composition varied from pure cuprous oxide at current densities below 0.1 mA/cm2 to 96 mole percent copper at 2.5 mA/cm2.

Epitaxial films of orthorhombic lead dioxide α-PbO 2 (Pbcn, a = 0.4971, h = 0.5956, and c = 0.5438 nm) were electrodeposited at room temperature on a [100]-oriented single crystal Au substrate (cubic, Fm3m, a = 0.4079 nm). The values of lattice mismatch are 21.9, 46.0, and 33.3% in the a, b, and c directions of α-PbO 2 , respectively. The films are [100]-oriented, with the a axis perpendicular to the substrate. Depending on the preparation conditions, the film was found to form two different in-plane orientations, with the unit cell of the PbO 2 structure rotated either 45 or 11.5° relative to the substrate. For the films deposited at low current density, only the first type of the in-plane texture is observed, while at high current densities both types are present in comparable amounts.