Anodization Of Nb Research Articles

Electrodeposition of Niobium Coatings on the Cryogyroscope Rotor

The discharge process of Nb(IV) complexes to Nb was studied by cyclic voltammetry. A galvanostatic electrolysis with the cathodic current density of 1.5·10−2 A cm−2 in the NaCl–KCl–NaF–K2NbF7 melt in contact with Nb anode was used for deposition of niobium coatings on the cryogyroscope rotor at temperature 1023 K, and time of process from 8 to 12 h. The coatings were continuous and smooth due to the special design of the cathode. The rotation speed of the stirrer was set to 35 rpm and did not change in all experiments. Such conditions made it possible to obtain coatings with the thickness up to 150 μm. The main characteristics of the niobium coatings such as purity, roughness, nonsphericity, and superconductivity were investigated.

Formation of One-dimensional Nb2O5Nanostructures by Anodization

In the present work, we investigate the anodization of Nb in a <TEX>$K_2HPO_4$</TEX> containing glycerol electrolyte at elevated temperatures (<TEX>$180^{\circ}C$</TEX>). Under optimized conditions, uniformly over the entire anodized surface, self-organized porous <TEX>$Nb_2O_5$</TEX> structures can be formed. The growth rate of highly ordered <TEX>$Nb_2O_5$</TEX> is <TEX>$1.7{\mu}m/min$</TEX> at beginning stage of anodization and the overall current efficiency is 70 %.

Enlarging the surface area of an electrolytic capacitor of porous niobium by Mg[sbnd]Ce eutectic liquid dealloying

To increase the surface area while decreasing the ligament size of an Nb anode pellet for use as a capacitor, we added Ce to an Mg melt; the dealloying reaction occurred at temperatures lower than 1023K, the previously lowest recorded temperature for such a reaction. By analyzing the dealloying kinetics, we found the optimum dealloying conditions to produce a minimum ligament size of 100nm in the Mg95.7Ce4.3 melt: 923K for 420s. Using these conditions, we increased the specific surface area of the Nb anode pellet to 4.3m2/g, which increased its mass-specific capacitance to 875,000μFV/g.

Formation of Highly Ordered Nanochannel Nb Oxide by Self‐Organizing Anodization

Supercapacitor: A highly aligned nanochannel Nb oxide structure can be formed by self-organizing anodization of Nb in a K2HPO4-containing glycerol electrolyte at elevated temperatures (180 °C). Under optimized electrochemical conditions, a high degree of ordering can be achieved. These layers can be used as supercapacitors (see figure).

Anodic formation of high aspect ratio, self-ordered Nb2O5 nanotubes

In the present work, we demonstrate the feasibility to form an aligned Nb(2)O(5) nanotube layer by self-organizing anodization of Nb in a NH(4)F-glycerol electrolyte. In order to achieve a nanotubular rather than a nanoporous layer, careful optimization of the anodization electrolyte is required. We show that only in a narrow window of electrolyte parameters highly aligned nanotubes of 50 nm inner diameter and several micrometres in length can be formed.

NaF 전해질 양극산화에 의한 마이크로콘 구조 니오븀 산화물 제조

In this study, we show that by anodization of Nb in NaF electrolytes microcone niobium oxide layers can be formed under a range of experimental conditions. It is found that a single NaF electrolyte leads to the formation of microcones. At 1 M NaF, 40 V, 1 h, well-ordered microcones were generated on Nb discs. XRD results show that the initially formed anodic oxide is amorphous, but an amorphous to crystalline transition occurs during anodization. For the formation of favorable microcones, it is considered that proper parameters such as electrolyte concentration, voltage, anodizing time are necessary according to the kind of electrolytes.

An electrochemical and surface analytical study of the formation of nanoporous oxides on niobium

In the present paper, the anodization of Nb in mixed sulphate + fluoride electrolytes resulting in the formation of a nanoporous oxide film has been studied. Chronoamperometry and electrochemical impedance spectroscopy have been employed to characterise in situ the kinetics of the oxidation process. In addition, the evolution of the layer structure and morphology has been followed by ex situ scanning electron microscopy. Particularly, local electrochemical impedance spectroscopy has been used to discern between the mesoscopic 2D and 3D distributions of time constants at the electrode surface. The similarity between local and global impedance spectra during anodic oxidation of Nb demonstrates the presence of an inherent 3D distribution of the high-frequency time constant, which is interpreted as in-depth variation of the steady state conductivity of the passive film. The experimental and calculational results are discussed in relation to the micro- and nanoscopic structure of the formed oxide.

Electric properties stability of NbO anode for new electrolytic capacitor

By using loading test and high temperature test, the electric-property stability of NbO anode and metal Nb anode were studied in comparison. The reason for higher stability of NbO anode was analyzed by thermodynamics and kinetics. The loading test was performed in 38% H 2SO 4 at 85 °C and 12 V for 10 d. The high temperature test was carried out at 250 °C in air atmosphere for 30 h. It is found that the NbO anode possesses higher ability to restrain crystallization film as compared with metal Nb anode. It is considered that, oxygen in NbO anode matrix restrains the migration of oxygen in Nb 2O 5 anodic oxidation film to matrix, and results in that the anodic oxidation film has higher stability.

Niobium and niobium nitride SQUIDs based on anodized nanobridges made with an atomic force microscope

We present a fabrication method of superconducting quantum interference devices (SQUIDs) based on direct write lithography with an atomic force microscope (AFM). This technique involves maskless local anodization of Nb or NbN ultrathin films using the voltage biased tip of the AFM. The SQUIDs are of weak-link type, for which two geometries have been tested: Dayem and variable thickness nanobridges. The magnetic field dependence of the maximum supercurrent I c( Φ) in resulting SQUIDs is thoroughly measured for different weak link geometries and for both tested materials. It is found that the modulation shape and depth of I c( Φ) curves are greatly dependent on the weak link size. We analyze the results taking into account the kinetic inductance of nanobridges and using the Likharev–Yakobson model. Finally we show that the present resolution reached by this technique (20 nm) enables us to fabricate Nb weak-links which behavior approaches those of ideal Josephson junctions.

Photoelectrochemical investigation of film formation at titanium and niobium anodes in acid fluoride media

The properties of the surface oxide films during electrodissolution of titanium and niobium anodes in acid fluoride media are investigated by photoelectrochemical and impedance techniques. In slow voltammetries a linear dependence of photocurrent signal on applied potential is observed, consistent with a constant film formation ratio; an estimate of the latter is given on the basis of capacity data. Phenomena of depassivation observed at the Nb anode during voltammetric and potential step experiments are characterised and attributed to instability of the oxide film. The photocurrent spectra of both surface oxides change in shape under polarisation, showing a limited decrease of the photoresponse for penetrating wavelengths close to the bandgap and a marked decay for the shorter, strongly absorbed wavelengths. The phenomenon may be attributed to formation of a duplex oxide film, with a compact photoactive layer in contact with the metal substrate and an outer layer at the film ∣ solution interface, rich in defects and possibly porous/hydrated, which acts as an optical filter.

Electrical transport properties of thin-film metal-oxide-metal Nb 2O 5 oxygen sensors

The electrical properties of thin-film metal-oxide-metal Nb 2O 5 oxygen sensors have been investigated in the temperature range 400–600°C. They are shown to be strongly dependent on the electrode material. With Nb electrodes, the cathode is a good electron injector. At low bias, the oxygen pressure dependence of the conductivity follows P(O 2) −1/ n with n equal 1.0 ± 0.2 over a pressure range extending at least from 10 5 to 10 Pa. A model is proposed explaining this behaviour by the presence of surface electron traps associated with chemisorbed oxygen. The films present a very large concentration of chemisorption sites as atmospheric oxygen is able to diffuse into the bulk through channels running between the Nb 2O 5 chains of the crystal structure. Above a certain threshold voltage, a non-linear regime where the current density is proportional to the square of the applied voltage is observed. This regime is explained by the anodic oxidation of the Nb anode. Cr and Pt electrodes behave like valve contacts: they are blocking at low voltage and injecting at high applied voltage. Structures shorter than 50 μm are shown to be depleted of their oxygen vacancies for electric fields in the range 10 3–10 4 V cm −1. The electrical admittance presents a steep non-linear double-injection regime above a certain threshol voltage. In this bias range the current density varies like V n with n ≥ 7. The threshold voltage is sensitive to the ambient and decreases when the sensor is exposed to an atmosphere with low oxygen concentration. It is shown that the migration of ionized oxygen vacancies induced by the electric field actually controls the electronic transport through the metal-oxide-metal structure. These results provide new insights into the capabilities and limitations of Nb 2O 5 sensors.

Design of variable phase velocity kinetic inductance delay lines and their measured characteristics when fabricated by a simple Nb based process

A simple design for superconducting kinetic inductance delay lines is presented. Delay lines were fabricated with a thin-film process involving only DC magnetron deposition and anodization of Nb. Phase-velocity measurements demonstrated wave slowing to less than 1/150 of the velocity of light in free space with associated impedances in the ohm range. Phase velocity changes on lines which were in physical proximity to long Josephson junctions and normal conducting lines were investigated. Variations larger than 10% of the equilibrium value were observed with junction-coupled lines under bias application. Locally heated lines exhibited changes exceeding a factor of two. Loss and phase velocity were determined as a function of bias conditions in both cases. Measured line loss was within expectations.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

ChemInform Abstract: INTERFACIAL PHENOMENA OF SOME TITANATE PHOTOANODES

AbstractAus Einkristallen hergestellte, mit Nb dotierte n‐Typ‐Photoanoden aus mechanisch poliertem n‐TiOzzNb (I) und aus mit LaCrO3 oberflächendotiertem n‐SrTiO3:Nb (II) wurden in photoelektrochemischen Zellen mit 0.5 M H2SO4 oderl M NaOH untersucht.

Interfacial Phenomena of Some Titanate Photoanodes

AbstractTwo types of titanate photoanodes are discussed, viz. mechanically polished n‐TiO2: Nb and hydrogen‐reduced n‐SrTiO3: Nb surface‐doped with LaCrO3. The anodes are investigated in acidic as well as in basic solutions. In addition the influence of ultraviolet irradiation is examined. Detailed equivalent circuits are proposed for both types of cells. Mott‐Schottky plots indicate the presence of a severely disturbed space‐charge region for both photoelectrodes. In the case of the mechanically polished n‐TiO2: Nb anode, the disturbance is attributed to surface roughness effects, whereas for the hydrogen‐reduced n‐SrTiO3: Nb, LaCrO3 anode, the existence of a nonuniform donor level is suggested.

Study of the Anodization of Niobium and Tantalum Superimposed Layers by 18O Tracing Techniques and Nuclear Microanalysis: I . 18O and Cation Depth Profiles

18O tracing techniques and nuclear microanalysis were used to study oxygen and cation movements during the anodization of Nb on Ta (Ta/Nb) and Ta on Nb (Nb/Ta) superimposed layers. Analysis of 18O depth distributions shows that the order of oxygen atoms is largely preserved for Ta/Nb systems, while it is partially inverted for Nb/Ta systems. The same dissymmetry holds for cations in these systems. For Nb/Ta, the fraction of the oxygen atoms taking part in the inversion of order depends on the formation conditions and on Ta layer thickness. Great similarities between Nb and these oxygen concentrations were observed in the various regions of oxide films. All the results are consistent with a short‐range migration for oxygen, as well as for cation transport, and a strong correlation appears between oxygen and cation migration.

High quality refractory Josephson tunnel junctions utilizing thin aluminum layers

Preparation of high quality all-refractory Josephson tunnel junctions based on Nb/Al-oxide-Nb and Nb/Al-oxide-Al/Nb structures is reported. Critical currents up to 1300 A/cm2 and Vm values up to 35 mV were obtained. The specific capacitance of these junctions is 0.06±0.02 pF/μm2. Junctions were fabricated using standard photolithography and a new plasma etching process coupled with anodization of Nb.

Anodization of Metals Through Thin Solid Electrolyte Films of Calcia Stabilized Zirconia

This paper shows that anodic oxidation of the metals Nb, Ta, and Al through thin solid electrolyte films of calcia stabilized zirconia (CSZ) is possible. The metal oxides grown are stoichiometric and the CSZ behaves like pure anodic oxide, since the electric field in CSZ in the 0.1–10 mA cm−2current density range is comparable with those in anodic oxides. Anodization of Nb|Ta|CSZ or Al|CSZ|Nb|Ta systems shows that only oxygen movements take place in CSZ during oxide growth (i.e., transport number of cations), while both oxygen and cations take part in ionic current in the metal oxides underlying and overlying the CSZ layer (i.e., ). Thus the transport number of cations can be considered as an intrinsic property of an oxide layer, independent of the nature and of the position of the other layers. Possible microscopic transport mechanisms for oxygen and cations through superimposed oxide films are discussed.