Bismuth Oxide Layer Research Articles

Size Effect of the Dielectric Properties in Bismuth-Based Layer- Structured Ferroelectric Films

Bismuth-based-layer-structured ferroelectric films have been formed epitaxially on Nb-doped SrTiO3 substrates by pulsed laser deposition (PLD). These films show an atomically smooth surface with a wide terrace of 100 nm–200 nm, as observed by atomic force microscopy (AFM) which is ideal for measuring such properties. Crystal growth apparently changes from the step-flow mode to the island-state mode according to the number of perovskite layers sandwiched by bismuth oxide layers. Additionally, the dielectric constant of the three film types, that is Bi2VO5.5 (n=1), Bi3TiNbO9 (n=2), and Bi4Ti3O12 (n=3) decreases proportionally with decreasing film thickness. It is considered that the size effect plays an important role in determining dielectric properties. Bismuth-layered ferroelectric films, with their atomically flat surfaces and accurate electrical properties, are an ideal material for applications in semiconductor devices.

Nucleation and growth of anodic oxide films on bismuth

Abstract Combined voltammetry and potentiostatic transient techniques have been used to study nucleation, formation and growth of thin oxide films on high purity polycrystalline bismuth in a borate buffer solution, pH=9.2. It was shown that the initial step in the formation of the continuous anodic layer of bismuth oxide on bismuth is a nucleation process. The potentiostatic technique was a valuable tool in its study. The oxide film nucleation kinetics were explained reasonably well through a 3D progressive nucleation and growth mechanism under diffusion controlled growth. Nucleation potential ( E AN ), steady-state nucleation rate ( AN 0 ) and the number density of growing centres ( N s ) are determined. A detailed mechanistic interpretation of the nucleation process and thickening of the anodic layer under potentiodynamic conditions was obtained using the criteria of cyclic voltammetry.

Substitution of lead into the bismuth oxide layers of the n = 2- and n = 3-aurtvillius phases

Ceramic materials of the n = 2- and n = 3-Aurivillius phases of type Bi 2SrM 2O 9 and Bi 4Ti 3O 12 were systematically substituted by Pb 2+. The simultaneous charge compensated incorporation was performed for n = 2 with the nominal compositions Bi 2 − xPb xSr 1 − xLa xM 2O 9 and Bi 2 − xPb xSr M 2 − xW xO 9 as well as for the single lead substituted systems Bi 2 − xPb xSrM 2O 9 − δ with M = Nb, Ta (0 ≤ x ≤ 1). For n = 3 the following groups of materials were synthesized: Bi 4−xPb xTi 3 − xNb xO 12, Bi 2 − xPb xLa 2Ti 3−xNbxO 12, Bi 2 − xPb x Sr 2 − xLa xTiNb 2O 12 (0 ≤ x ≤ 1) and Bi 2Sr 2 − yPb yTiNb 2O 12 (0 ≤ y ≤ 2). The powder X-ray diffraction diagrams were single phased for all materials, thus exhibiting a solid solution behavior over the whole range of substitution but for the single lead substituted n = 2 systems. Structural investigations by X-ray powder diffractometry were carried out with different space groups and ordering schemes in order to verify the incorporation of the isoelectronic Pb 2+ for Bi 3+ in the bismuth oxide layers. A partially disordered distribution of La, Pb and Bi in Bi 2 − xPb xLa 2Ti 3 − xNb xO 12 and ordering effects of Ti/Nb in Bi 2 Sr 2 − yPb yTiNb 2O 12 were indicated.

Calcium-doping effect on temperature coefficients of dielectric constants in SrTiO3 capacitors

SrTiO3 ceramic capacitors were studied to improve the temperature coefficient, τ, of dielectric constants without decreasing the dielectric constants. It was indicated that an addition of calcium in an insulating reagent improved τ. From scanning electron microscopy and energy-dispersive X-ray analysis measurements, the origin of this improvement was ascribed to the following layers: (1) the oxide layers which were formed at the grain boundaries, and (2) the bismuth-oxide layers which were formed on the sample surface.

XPS Evidence for the Incongruent Surface Oxidation of Minerals in the Pd-Te-BiSystem

Selected members of the Pd–Te–Bi system (PdTe, PdTeBi and PdBi) have been synthesized from their constituent elements, their structure and phase integrity confirmed by x-ray diffraction and optical microscopy and their initial oxidation in air under ambient conditions investigated by means of XPS. Prior to air exposure, the Pd core-electron binding energies were 0.6–1.0 eV higher than the corresponding values for the pure metal, while the core-level shifts for the alloying elements were very small. In each case, oxidation was quite rapid, but the palladium did not appear to be directly involved in the initial reaction; no change in the Pd 3d spectrum other than in its intensity was observed, notwithstanding the formation of significant amounts of tellurium oxide and/or bismuth oxide. The electron spectra were consistent with an incongruent oxidation reaction leading to the formation of a layer of tellurium and/or bismuth oxide covering a palladium-enriched substrate.

Aurivillius phase formation in Nb2O5 ? and Bi2O3 ? doped BaTiO3

The reaction sequence in the BaTiO3−Nb2O5−Bi2O3 system leading to the core-shell microstructure that causes the temperature-stable dielectric response has been examined using X-ray diffraction. The starting oxides react to form bismuth oxide layer Aurivillius phases at low temperatures which, in turn, react with remnant oxides to form the tetragonal tungsten bronze phase, Ba4Bi2Ti4Nb6O30, which acts as the source of dopants responsible for core-shell formation.

Electron tunneling microscopy: a direct probe of metal substitution in BiSrCaCuO superconductors

Scanning tunneling microscopy (STM) exploits the extreme distance sensitivity of electron tunneling to achieve atomic resolution imaging of surfaces. The ability of STM to probe directly materials on the atomic scale has been exploited to elucidate the structural effects of metal substitution in the copper oxide superconductor Bi 2Sr 2CuO 6. A series of Bi 2Sr 2CuO 6 single crystals containing lead substituted in the bismuth-oxide layer have been prepared, and the structures of these materials have been characterized by STM. The measurements show that lead-substitution induces complex changes in the structural order of the parent compound. Comparisons of these data with electron diffraction measurements highlight the importance of local crystallography, which STM provides, in studying the chemistry of inorganic materials.

Electrical anisotropy and a plausible explanation for dielectric anomaly of Bi 4Ti 3O 12 single crystal

The electrical anisotropy of layer-structured bismuth titanate (Bi 4Ti 3O 12) has been investigated by measurements of Seebeck coefficient, dielectric permittivity, DC conductivity, and complex impedance on single- and polycrystalline samples, and a plausible explanation for the origin of dielectric anomaly below Curie temperature has been suggested. A large anisotropy in the dielectric permittivity, DC conductivity and activation energy for charge transport was observed between the parallel/perpendicular direction to the bismuth oxide layer ((Bi 2O 2) 2+ layer. Complex impedance and modulus spectroscopy on single crystals in the direction perpendicular to the bismuth oxide layer below the Curie temperature confirmed that there are large differences in the electrical resistivity and, in particular, capacitance between the parallel/perpendicular direction to the bismuth oxide layer, which is assumed to be due to the difference in the electrical nature of the bismuth oxide layer and the pseudo-perovskite block. The dielectric anomaly below the Curie temperature is thought to originate from the space charge due to the thermally agitated polarization fluctuation.

Initial growth mechanism of BiSrCaCuO thin films on SrTiO 3(110) surfaces studied by in-situ reflection high energy electron diffraction observation

The initial growth mechanism of Bi 2Sr 2Ca n−1 Cu n O x (BSCCO) films was investigated on SrTiO 3(110) surfaces by in-situ reflection high energy electron diffraction (RHEED) observation. The orientations in the BSCCO thin films were controlled by the flux of metal elements in the initial growth stage. A preceding deposition of Bi produced a RHEED pattern indicating the formation of a bismuth oxide layer which assisted the growth of a half-unit cell at the beginning of codeposition. A ( Bi: Sr: Ca: Cu =) 2:2:1:2 phase (117) orientation mixed with a c axis orientation was obtained. A preceding deposition of Sr, Ca and Cu produced a pattern indicating the formation of (Sr 1− x Ca x ) 2CuO 3 and caused epitaxial growth just after the start of codeposition, based on the structural relationship between the substrate and the perovskite structure part of the films. A 2:2:1:2 phase (119) orientation was formed.

The first doping of lead 2+ into the bismuth oxide layers of the aurivillius oxides

Taking as the starting material the Aurivillius oxide Bi 2SrNb 2O 9 , it has been demonstrated for the first time that the ( Bi 2O 2 ) 2+ layers can be doped with the Pb 2+ cation, which also possesses a stereochemically active lone pair. Samples of composition Bi 2−xPb xSrNb 2O y have been prepared and yield a solid solution over the entire range 0≤x≤2. The substitution of Pb 2+ is accompanied by the occurrence of oxygen vacancies, in order to compensate the reduced cation charge.

Phase transformations in the BiSrCaCuO system for thick films from a novel nitrate paste

This study focuses on the phase changes occurring in superconducting thick films of Bi2Sr2Ca1Cu2Ox printed from a novel nitrate paste on single-crystal MgO. By optimizing the firing profile, the ratio of the 2.4 nm to 3.0 nm phase could be controlled to achieve reproducibleTo values of 85 K. A model for the 2.4 nm to 3.0 nm phase transformation is proposed, based on SEM and X-ray diffraction data. Two unit cells of the 2.4 nm phase may transform to one 3.0 nm phase unit cell by losing two bismuth oxide layers and one strontium oxide layer. Sr, Bi-rich particles were observed by SEM after the transformation. The degradation of the thick films with ageing at room temperature may be related to possible SrCO3 and/or CaCO3 formation.

Phase transitions and dielectric properties in some compounds with bismuth oxide layer structure

Abstract Solid solutions deriving from ferroelectric Bi3TiNbO9 by cationic substitutions of La3+ for Bi3+ and (Ti4+,W6+) for Nb5+ have been synthesized using a standard ceramic method. Evolutions of unit cell parameters and dielectric properties as a function of the substitution are given. All compounds show a ferroelectric phase transition, the temperature of which decreases with increasing substitution rate. The relations between the crystal chemical data and the dielectric behavior are discussed.

High-Adhesion Thick-Film Gold Without Glass or Metal-Oxide Powder Additives

The problems of bonding gold to glass or ceramic are discussed. Glass-to-gold bonding is necessary to obtain the adhesion of gold conductors in thick- or thin-film circuits. The history of thick-film gold conductors is reviewed from the frit-bonded to the reactively bonded to the mixed-bonded system, Which is the current standard. A new different method of achieving gold thick-film adhesion is presented. This adhesion is caused by a molecular layer of cadmium and bismuth oxide on the surface of gold. The coating is Obtained during firing from base metal resinates contained in the ink vehicle. Such surface active (surfactive) gold ink without frit or metal-oxide powder additives provides optimized adhesion and wire bondability when used as a top conductor in multilayer circuits.

Ellipsometric examination of the oxidation of vacuum-deposited bismuth films

An investigation has been carried out of the surface structure and oxidation of thin films of bismuth vacuum deposited onto heated glass substrates. Temporal variations in the optical properties of thin films of bismuth have been shown to be due to the growth of an extraneous surface layer of bismuth oxide. Detailed ellipsometric measurements have made it possible to monitor the rate of growth of this layer and to determine its refractive index throughout the visible spectrum.

Path of oxygen in a bismuth molybdate lattice during selective oxidation

The path of oxygen in a bismuth molybdate lattice during selective oxidation of hydrocarbons to unsaturates was derived from calculated interaction potentials. Minimum energy requirements indicated that oxygen bonded to a bismuth ion is removed by the hydrocarbon and replaced by an oxygen ion from an intermediate layer between charged bismuth oxide and molybdenum oxide layers. The molybdenum oxide replaces this oxygen, and this oxygen in turn is replaced from external reactant oxygen. Diagrams, graphs, tables, and 21 references.

ChemInform Abstract: NUCLEATION AND GROWTH OF ANODIC OXIDE FILMS ON BISMUTH. I. CYCLIC VOLTAMMETRY

AbstractDie frühen Stadien der Bildung einer kontinuierlichen anodischen Oxidschicht auf einer festen Bi‐Elektrode werden im pH‐Bereich 5‐14 untersucht.

Nucleation and growth of anodic oxide films on bismuth—I. Cyclic voltammetry

The early stages in the formation of a continuous anodic layer of bismuth oxide on a solid bismuth electrode, in the pH range 5–14, were studied. The oxide covered the surface by the simultaneous thickening and spreading of patches. The metal surface was classified into two different areas with different overvoltage for oxide nucleation. The ratio of the two areas varied according to the history of the surface. The thickening of the newly formed layer (final thickness ∼20 nm) followed the high-field growth law i = Aexp(BE) where E is the field in the oxide layer, with B = (2.0 ± 0.5) × 10−6 V−1 cm. This value of B gives an activation distance for high-field ion transport of 0.2 nm, comparable to the radius of a lattice site and much smaller than that obtained previously, for much thicker films. Dissolution of the film, giving breakdown of the oxide layer and pitting of the metal, occurred for pH<8. The thickness of the anodic film was thus limited to only 4 nm at pH 5. Cathodic reduction of the anodic oxide resulted in a porous metal surface. The current—voltage curve for the reduction often had a complex shape, which was related to the morphology of the original anodic layer.

Crystal structure of (Sr, Ba)Bi 2Ta 2O 9

The crystal structure of (Sr 0.9Ba 0.1)Bi 2Ta 2O 9 has been refined to elucidate the nature of the lower phase transition observed in even-layered members of the bismuth titanate family. Least squares analysis based on x-ray and neutron diffraction intensities led to an R-factor of 0.13 for 1135 reflections. Bismuth strontium barium tantalate is orthorhombic, space group A2 1am, with a = 5.504, b = 5.488, c = 25.06 A ̊ , and Z = 4. Near the lower transition, five short Bi-O bonds are retained in the bismuth oxide layer, but distortions in the perovskite are reduced considerably, with the Ta ion displaced just 0.05Å from the center of the octahedron.

Bismuth titanate solid solutions

Solubility limits have been determined for a number of solid solutions based on ferroelectric Bi 4Ti 3O 12. Several di- and trivalent ions substitute readily for bismuth in the perovskite layer, but the octahedral site and the bismuth oxide layer are far less flexible, tolerating only very limited solid solution. Dimensional mismatch between the perovskite layer and the bismuth oxide layer provides an adequate explanation of the structural stability.

La-Doped BaTiO&lt;sub&gt;3&lt;/sub&gt; Ceramics with Bi&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; as a Grain Boundary Element

It is known that sintered bodies of semiconducting barium titanates or its solid solutions have a large positive temperature coefficient of resistivity above and near the Curie temperature. They have a negative temperature coefficient of resistivity normal as usual semiconductors below the Curie temperature. At the Curie temperature the tetragonal to cubic transition takes place and the resistivity anomaly around the temperature has been related to the transition. At the transition temperature, orthorhombic to tetragonal, however, no anomaly in the resistivity-temperature characteristic has been found on the sintered bodies reported so far.The present authors modified the texture of sintered bodies of semiconducting barium titanate with bismuth oxide penetrated along grain boundaries. When non-ohmic contact electrodes were applied to the texture modified specimens another anomaly in the resistivity-temperature characteristic appeared above the orthorhombic to tetragonal transition temperature in addition to the anomaly above the Curie temperature. The nonlinear current-voltage and capacitance-voltage characteristics measured on present specimens with asymmetric electrodes (non-ohmic contact electrode to the one side and ohmic contact to the other side), showed the existence of a surface barrier-layer in the interface between the non-ohmic electrode and the body with texture modified. The nonlinear curve in the capacitance-voltage characteristic was not expressed by the relation 1/C2=2(Vd-V)/eεsNd (Vd is a built-in voltage at a barrier, εs is a dielectric constant in a barrier-layer and Nd is the density of ionized donor centers) above a certain reverse bias which was dependent on a measuring temperature. It seems reasonable to assume that the surface barrier-layer is made up of a inversion layer and a bismuth oxide layer. The barrier gave rise to the anomaly around a room temperature. Under a higher electric field the effect of the surface barrier becomes negligible small compared with the effects by barriers given across the grain boundaries in the sintered body which is considered to give rise to the anomaly above the Curie temperature. It may be considered that by the addition of bismuth oxide the concentration of trap centers changed; the concentration of trap centers affects the height and width of the barrier between semiconducting grains and of the barrier between the non-ohmic electrode and the pellet surface.