Nb Source Research Articles

Niobium uptake by {P2W12} polyoxoanion with [NbO(C2O4)2(H2O)2]− as Nb source

Reaction of (NH4)[NbO(C2O4)2(H2O)2]·3H2O with K12[H2P2W12O48]∙24H2O in aqueous solution at pH 1.7 leads to the formation of mixed Nb/W species based on [(P2M18O60)2(µ-O)2]n− (M is a Nb/W mixture, when Nb ratio ranges from 6 to 8 and charge differs from 14- to 16- correspondingly) archetype. Direct crystallization from the reaction media results in colorless crystals with the composition formulated as K9(NH4)5[cis-(P2W15Nb3O61)2]·48H2O (1). Crystallization in the presence of (NMe2H2)Cl yields two phases (2a and 2b), containing the same [trans-(P2W14.7Nb3.3O61)2]14.6− anions but different cation/H2O compositions. Both phases are present in a mixture with bulk composition corresponding to (NMe2H2)14.6[P2W14.7Nb3.3O61]2·28H2O (2). The solution behavior of 1 and 2 was studied with HR-ESI-MS and HPLC-ICP-AES. During XRPD study of 2 we found blue coloration of the thin film of the complex. This effect has only surface nature and was studied by diffuse reflectance spectra.

Unexpected formation of delta (δ) phase in as-cast niobium-bearing superalloy at solution annealing temperatures

The annealing of as-cast Inconel 718 superalloy at high solution annealing temperatures for short holding durations was studied. It was found that the needle-shaped δ phase formed from the eutectic constituent, which was followed by the dissolution of this phase by continued annealing. In fact, the formation of δ phase was characterized as an intermediate stage for the dissolution of Laves phase and back-diffusion of the segregated elements from the interdendritic regions. Thermodynamics analysis revealed that the upper temperature limit for the formation of δ phase is dependent on the Nb content. During annealing, the Laves phase started to dissolve, which resulted in the rejection of Nb to the interlamellar austenite, which was characterized as the primary Nb source for the observed local increase in the formation temperature of δ phase

Characteristics of exfoliated HNb3O8 nanosheet derived from amorphous niobic acid and its application to dehydration of 2-heptanol

The synthesis of exfoliated HNb3O8 nanosheet (eHNb3O8) generally starts from the mixing of K2CO3 with crystalline Nb2O5 and involves a very routine procedure in subsequent multi-steps. Herein, we report for the first time the use of niobic acid (NBA, Nb2O5nH2O) as Nb source for the preparation of final eHNb3O8. Different from the analogue derived from crystalline Nb2O5, the prepared nanosheet contains a very small amount of potassium ion and exhibits high stability in consecutive runs for the dehydration reaction. The linkage between these two features is confirmed by the inferior stability of potassium-deficient eHNb3O8 samples prepared via prolonged proton-exchange. When a series of niobate materials are examined, the remarkable finding is the higher K/Nb ratio in NBA-derived KNb3O8 than the theoretical value. This is attributed to the acidity of amorphous NBA by which the carbonate ion of K2CO3 is decomposed into CO2 in the preparation of the solid mixture K2CO3-NBA. These more intercalated K+ cannot be all displaced with proton by the general ion-exchange process employed for Nb2O5-derived eHNb3O8. Consequently, the proposed model suggests that the potassium ion remaining in NBA-derived eHNb3O8 acts as a ligating element to tie up a single, exfoliated nanosheet into several.

Comparative study of niobium-containing hexagonal mesoporous silicas prepared using different niobium sources

Two groups of niobium-containing hexagonal mesoporous silica (Nb-HMS) samples were prepared hydrothermally using niobium oxalate and niobium ethoxide as Nb source, respectively. The samples were characterized by XRD, N2-adsorption, ICP-AES, UV-Vis, respectively. They were also evaluated by the epoxidation of cyclohexene with cumene hydroperoxide (CHP) as oxidant. It is revealed that the samples possess typical hexagonal mesoporous structure in which most of Nb species exist in the form of framework pentahedral coordinated state. Meanwhile, the Nb-HMS samples from niobium ethoxide give more excellent catalytic performance than those from niobium oxalate. It is likely because that the former samples have a higher total amount of Nb species and a higher proportion of isolated framework Nb species. Accordingly, niobium ethoxide is a better niobium source than niobium oxalate.

A Novel Low Temperature Synthesis of KNN Nanoparticles by Facile Wet Chemical Method

Sodium potassium niobate (KNN) (K0.5Na0.5NbO3) nanopowder with a mean particle size of about 20 - 30 nm was synthesized by wet chemical route using Nb2O5 as Nb source. A solution of K, Na and Nb cations was prepared, which resulted in a clear gel after the thermal treatment. Phase analysis, microstructure and morphology of the powder were determined by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR) and Field Emission Scanning Electron Microscopy (FESEM). The obtained gel was first analyzed by Thermo Gravimetric Analyzer (TGA) and Differential Scanning Calorimetry (DSC), and then calcined at different temperatures of 400℃, 500℃, 600℃ and 700℃. The X-Ray Diffraction (XRD) patterns of the synthesized samples confirmed the formation of the orthorhombic crystal phase of K0.5Na0.5NbO3 at 500?C, a temperature significantly lower than that typically used in the conventional mixed oxide route. The process developed in this work is convenient to realize the mass production of KNN nanopowders at low cost and suitable for various industrial applications.

Hybrid co-deposition of molybdenum doped niobium pentoxide (NbxMoyOz) thin films

Mixed valent thin films, consisting of optically absorbing metallic cations within a dielectric matrix, possess a variety of optical and electronic properties that can be tailored through variation of dopant concentration and chemistry. This work details the reactive magnetron co-deposition of mixed valent NbxMoyOz thin films, systematically doped with optically absorbing Mo5+ cations, through adjustment of the molybdenum source power. Control over the concentration the Mo5+ valence state was achieved through decreases in the oxygen partial pressure facilitated via oxygen chemisorption by the molybdenum sputter flux at power levels of 0, 20, 40, 60, 80, and 100 W, while the Nb source was operated concurrently at a constant sputter power of 200 W. The resulting films, roughly 100 nm in thickness, were characterized using variable angle spectroscopic ellipsometry as well as x-ray photoelectron spectroscopy in order to derive a process-property relationship among molybdenum source power and its effects on the refractive index, extinction coefficient, optical band gap, as influenced by the relative concentrations of Mo5+, Mo6+, and Nb5+ cations. Increases in the molybdenum source power from 0 to 100 W allow for tailorability of the refractive index, 2.29 ≤ n550 ≤ 2.34, extinction coefficient, 0.00 ≤ k550 ≤ 0.02, and optical band gap, 3.05≤Eg ≤ 3.48 eV. The co-deposition procedure used within this work affords the ability to systematically adjust the content of the absorbing Mo5+ cations, from 0 to 3 at. %, within a dielectric matrix comprised of MoO3 and Nb2O5, presenting several opportunities in increasing the design-space for both optical coatings and electrochromic devices.

Size-controllable synthesis of lithium niobate nanocrystals using modified Pechini polymeric precursor method

Nanopowders of lithium niobate (LiNbO3, LN) were synthesized by a water-based modified Pechini method, in which Li2CO3 and ammonium niobate (v) oxalate hydrate (C4H4NNbO9·xH2O) are used as the Li and Nb source materials, respectively. The kinetics of formation of the intermediate gelatinous precursor was studied by thermal gravimetry and differential scanning calorimetry. The LN nanoparticles produced by calcining of the gel at various temperatures were characterized by X-ray diffraction and scanning electron microscopy. The effect of the calcination temperature on the morphology and structure of LN nanoparticles produced is investigated. The particle and crystallite sizes of the LN prepared could be controlled in the range of 20–250 nm by changing the calcination temperature of the gelatinous precursor.

Mesoporous niobium-silicates prepared by evaporation-induced self-assembly as catalysts for selective oxidations with aqueous H2O2

Hydrothermally stable mesoporous niobium-silicates Nb-MMM-E have been first prepared following the convenient and versatile evaporation-induced self-assembly (EISA) methodology. The new materials have been characterized by elemental analysis, XRD, low-temperature N2 adsorption, SEM, XPS, DRS UV–vis, and Raman techniques. DR UV–vis spectroscopy enabled differentiation between isolated and oligomerized Nb centers on the silica surface. Use of niobium(V) ethoxide modified with acetylacetone (acac) as a Nb source favored the formation of dimeric and/or small oligomeric Nb centers on the surface of mesoporous silica while ammonium niobate(V) oxalate coupled with acac gave mostly site-isolated Nb species. The Nb-MMM-E materials catalyzed selectively oxidation of various unsaturated compounds of interest for fine and specialty chemistry using the green oxidant – aqueous hydrogen peroxide. Epoxidation of both electron rich and electron deficient CC bonds could be accomplished over Nb-MMM-E. While catalysts with isolated Nb centers were preferable for the selective formation of epoxides sensitive to ring opening and overoxidation, both single site and oligomerized Nb centers were equally effective for the production of relatively stable epoxides. The truly heterogeneous nature of the catalysis over Nb-MMM-E and absence of Nb leaching into solution have been proved by hot filtration tests coupled with elemental analysis. The catalysts could be easily recovered by filtration and reused several times without significant deterioration of the catalytic performance.

Steps in growth of Nb-doped layered titanates with very high surface area suitable for water purification

Nb-doped layered titanates, as highly efficient adsorbents, have been synthesized by hydrothermal reaction for variable duration and at 150 °C in a highly alkaline solution with NbCl5 as the Nb source. The results have shown the formation of nanosheets already after 1 h of hydrothermal processing, but morphology and phase composition change as the reaction proceeds. The prepared layered titanates have been structurally investigated via scanning and transmission electron microscopy, X-ray diffraction, as well as Raman and Fourier transform infrared spectroscopies. The steps of layered titanate growth have been followed and an intermediate layered anatase phase is identified. Thus optimized growth of mesoporous titanate materials with 10% Nb atomic content present very high specific surface area of 345.3 m2 g−1, and perform as very efficient adsorbents for wastewater treatment applications.

Modeling of neutral beam injection heating and current drive during the ramp-up phase in KSTAR

For flexible control of the plasma pressure and the current profiles, which are essential for a high performance plasma with long pulse operation, KSTAR is going to implement several heating and current systems, which include Neutral Beam Injection (NBI), Ion Cyclotron Resonant Heting (ICRH)/Fast Wave Current Drive (FWCD), Lower Hybrid Current Drive (LHCD), and Eclectron Cyclotron Heating (ECH)/Electron Cyclotron Current Drive (ECCD). Here, the NBI system is typically used for the central heating and current drive. For the time being, only one NBI device (composed of 3 sources) is available in KSTAR. The first two sources were successfully commissioned in 2010 and 2013. The last source will be installed in 2014. In this work, we present a simulation study of the heating and current drive of the first NBI system (3 sources) during the ramp-up phase. We consider two different NBI configurations (low and high beam energy). The simulation is performed with NUBEAM, a well-recognized Monte-Carlo code. Several different types of KSTAR target equilibria (scan from lower to higher plasma density) are used for the calculation of the current drive, the heating and the different NB losses (shinethrough, charge exchange and bad orbit). The study shows the dependency of those quantities on the plasma density, the position of the NB source and the beam energy. It also shows that because of the shinethrough loss is too high, each NB source cannot be used when the plasma density is under a certain threshold. This study can be used to determine the starting time of the different NB sources during the KSTAR ramp-up phase.

The fine-grained KNN–LN ceramics densified from nanoparticles obtained by an economical sol–gel route

(1−x)(K0.5Na0.5)NbO3–xLiNbO3 ((1−x)KNN–xLN) nanoparticles with the mean particle size about 20–30nm have been prepared by an economical sol–gel routes using Nb2O5 as Nb source. Due to the high sintering ability of nano-particles, fine-grained KNN–LN lead-free ceramics have been densified at the temperature below 1000°C. X-ray diffraction analysis indicated that the phase structure of the ceramics changed from orthorhombic to tetragonal at x=0.08–0.10. When the x reached 0.10 and above, the perovskite structure could not be maintained and the impurity phases of K3Li2Nb5O15 and LiNbO3 appeared, indicating that x=0.10 is near the solubility limit. Optimized parameters, such as d33=170 pC/N and kp=0.40, were achieved in 0.90KNN–0.10LN systems. Due to the merits of fine-grained structure and low sintering temperatures, it will be helpful to the application of KNN–LN materials for lead-free multilayer piezoelectric actuator.

LOW-FIRING SOL–GEL DERIVED Mn-DOPED 0.92(K0.5Na0.5)NbO3–0.08LiNbO3 LEAD-FREE CERAMICS WITH ENHANCED PIEZOELECTRIC PROPERTIES

Mn -doped 0.92( K 0.5 Na 0.5) NbO 3–0.08 LiNbO 3 (0.92KNN–0.08LN) lead-free piezoelectric ceramics have been prepared by a developed sol–gel routes using Nb2O5 as Nb source. Due to the high quality of gel precursor, Mn -doped 0.92KNN–0.08LN nanopowders with the mean particle size about 20 nm were obtained at 500°C. The addition of Mn can promote the densification of nanopowders effectively at 950°C, and also influences in a pronounced way both the crystal structure and microstructure of the materials. With the increase of the amount of Mn addition, 0.92KNN–0.08LN ceramics are transformed from dominant orthorhombic to coexistence of the orthorhombic and tetragonal phases, and the grain sizes are enhanced simultaneously. Optimized parameters, such as d33 = 212 pC/N and k p = 0.46, were achieved in 0.2 Mn -doped 0.92KNN–0.08LN systems, which are good candidate material for lead-free piezoelectric devices.

Preparation of Barium Titanate–Potassium Niobate Nanostructured Ceramics with Artificial Morphotropic Phase Boundary Structure By Solvothermal Method

Barium titanate (BaTiO3, BT)–potassium niobate (KNbO3, KN) (BT–KN) nanostructured ceramics with a distorted interface region, i.e., artificial morphotropic phase boundary (MPB) structure, were prepared by the solvothermal method. The results of the optimization of reaction conditions showed that the metastable region of only KN crystal growth was obtained using a mixture of KOH and K2CO3 as the K source and Nb2O5 as the Nb source in ethanol. Moreover, KN formation under the metastable region using a particle compact composed of a mixture of BT and Nb2O5 particles as substrates resulted in the successful preparation of BT–KN nanostructured ceramics with an artificial MPB region and a porosity of around 35%. This is the first report on the preparation of ceramics with a heteroepitaxial interface between BT and KN below 230 °C.

Crystal structure and orthorhombic–tetragonal phase transition of nanoscale (Li 0.06Na 0.47K 0.47)NbO 3

Lead-free nano (Li 0.06Na 0.47K 0.47)NbO 3 powders, with pure perovskite structure and various grain sizes between about 30 and 60 nm, have been successfully synthesized by a novel sol–gel method, in which Nb 2O 5 was used as the Nb source. The refining XRD and Raman spectra were used in combination with TEM to investigate the evolution of lattice structure and phase transformation behavior as a function of grain size. The results demonstrated that the growth process of grains has been divided into two stages, and the distortion of unit cell apparently decreases with decreasing grain size. At around 35 nm, the phase structure of (Li 0.06Na 0.47K 0.47)NbO 3 changed from orthorhombic to tetragonal. This phenomenon is related to a grain size-induced structural phase transition. For the well accepted wisdom that niobates get super piezoelectric properties in orthorhombic–tetragonal transition region, our results suggested a critical size for the application of (Li 0.06Na 0.47K 0.47)NbO 3 in nano piezoelectric devices.

Sol–gel synthesis and characterization of lead-free LNKN nanocrystalline powder

A kind of lead-free nanocrystalline powder, (Li 0.06Na 0.47K 0.47)NbO 3 (LNKN), has been prepared by a newly developed sol–gel method using Nb 2O 5 as the Nb source. Phase analysis, microstructure and morphology of the powder were determined by X-ray diffraction (XRD), Fourier transform infrared (FTIR), Raman, transmission electron microscope (TEM) and high-resolution transmission electron microscopy (HRTEM). The experimental results showed that pure perovskite phase was formed at the temperature as low as 500 °C. Besides, the obtained powder belonged to tetragonal symmetry, and the mean particle size was as small as 20 nm. It is believed that the high-quality gel precursor and low processing temperature play a key role in the formation of the LNKN nano-particles. The process developed in this work was convenient to realize the mass production of LNKN nano-powders at low cost.

Direct Synthesis and the Morphological Control of Highly Ordered Two-Dimensional P6mm Mesoporous Niobium Silicates with High Niobium Content

Here we demonstrate the preparation of highly ordered two-dimensional P6mm mesoporous niobium silicates with unprecedented loadings of niobium in the silica framework (up to nSi/nNb ratio of 6.1) and highly winding morphologies maintaining regularly aligned arrays of nanochannels through a simple adjustment of the molar water to hydrochloric acid ratio (nH2O/nHCl) in the synthesis gel using nonionic surfactant as a template in a highly acidic medium. X-ray diffraction (XRD), N2 adsorption, high-resolution scanning electron microscopy (HRSEM), energy-dispersive spectrometry (EDS), and high-resolution transmission electron microscopy (HRTEM) results provided strong evidence of the presence of highly ordered two-dimensional structure in the NbSBA-15 materials with a very high content of niobium and winding morphologies, whereas UV−visible diffuse reflectance spectroscopy (UV−vis DRS) confirmed the presence of tetrahedrally coordinated niobium in the silica framework. Moreover, the loading of Nb in the silica framework can be controlled by a simple adjustment of the nH2O/nHCl and the amount of Nb source in the synthesis gel. Thus, a hitherto unachieved loading of niobium in the silica framework with a controlled manner, considered by many researchers to be impossible to achieve for the highly ordered mesoporous SBA-15 materials because of the highly acidic synthesis condition and the framework connectivity constraints, has been reported. We also found that the Nb incorporation could be a way to control the morphlogy of the NbSBA-15 materials. The morphology of the materials changed from rod to semispherical to “winding road” shape with decreasing the nSi/nNb from 22.5 to 6.1. Moreover, the detailed mechanism on the morphological control as a function of Nb content has also been proposed. This simple one-step technique to control the morphology, which would be of general interest for the application requiring the materials with different morphology, and Nb loading in a highly acidic medium synthesis have not been reported so far.

Characteristics of low energy atom and molecule beams generated by the charge exchange reaction

A low energy NB source, which consisted of a surface wave plasma (SWP) source and two large diameter carbon electrodes, was developed for damageless etching of ultralarge-scale integrated devices. Ion beams were extracted from the SWP using two carbon electrodes, accelerated and injected to the process chamber, and then neutralized without energy loss by a charge exchange reaction. The energy distribution functions of an Ar ion beam and an Ar atom beam was observed using a quadrupole mass spectroscope equipped with an energy analyzer. The energy of the Ar ion beam and the Ar atom beam was controlled by the acceleration voltage. N2 ion and N ion beams were also extracted from a nitrogen plasma source. The intensity ratio of the N ion beam to the N2 ion beam was 5:9, indicating that N ions were efficiently generated in the nitrogen SWP. The N2 ion and N ion beams were changed to N2 molecule and N atom beams, respectively, through a charge exchange reaction without energy loss. The energy of these beams was controlled by the acceleration voltage and was in the region less of than 100eV. When the acceleration voltage is higher than 40V, not only the primary peaks due to the N2 ion beam or N ion beam were observed but also a low energy second peak was observed in the energy distribution. The energy of the low energy second peak was controlled by the acceleration voltage. It was concluded that the low energy second peak corresponds to the N2 molecule ion beam and the N ion beam, which is extracted from the second plasma generated in the space between the two carbon electrodes.

Synthesis of fine Pb(Fe 0.5Nb 0.5)O 3 perovskite powders by coprecipitation method

Lead iron niobate, Pb(Fe 0.5Nb 0.5)O 3 (PFN) is an optimal material for multilayered ceramic capacitors (MLCCs). Fine lead iron niobate powders with average size of 500 nm were prepared from the precipitation precursor. In the experiment, Nb 2O 5 was used as Nb source to substitute Nb alkyloxide or oxalate and successfully converted into aqueous Nb 5+ solution. The results shows that the perovskite PFN was emerged at a temperature as low as 400 °C, and pure perovskite was obtained at the temperature of 800 °C. The formation of perovskite at a low temperature was attributed to the core–shell structure in the precipitates of hydroxide. Besides, the particles of perovskite PFN show the good chemical stoichiometry and small size of 300–500 nm.

New Nb-containing SBA-3 mesoporous materials—Synthesis, characteristics, and catalytic activity in gas and liquid phase oxidation

The synthesis and characterization of NbSBA-3 mesostructured materials – the first hexagonally ordered mesoporous molecular sieves without extra framework Nb-oxide phase – are described in this paper. The effect of the synthesis medium (basic or acidic) and Nb source in the efficiency of niobium incorporation is discussed. A higher Nb content in the final material is reached when Nb(V) chloride is used instead of Nb(V) ammonium trisoxalate complex in the synthesis. All NbSBA-3 materials prepared in this work are very attractive catalysts in ODH of propane and epoxidation of cyclohexene and more effective than the corresponding NbMCM-41 and NbSBA-15 catalysts.

Growth and intermixing of Nb on Fe(110) and Fe on Nb(110)

The growth system Nb/Fe and the reversed system Fe/Nb were studied on the (110) surface using Scanning Tunneling Microscopy (STM). For Nb/Fe(110) we present in situ STM results as a direct evidence of a Nb/Fe exchange mechanism at temperatures above 400 K that leads to the formation of a surface alloy. Since the experiments on Nb(110) were done on Nb buffer layers the fabrication of those is discussed. We show that besides Al 2O 3 (112¯0) wafers a W(110) single crystal can serve as a support for Nb(110) buffer layers which is more convenient for STM measurements. The niobium oxide adlayer that is present on nearly all Nb surfaces can be avoided by thorough degassing of the Nb source. Results on Fe/Nb(110) are discussed in the temperature range from room temperature (RT) to 1000 K. At RT no intermixing of Fe and Nb was observed and with very low deposition rates epitaxial films can be grown. An ordered dislocation network was observed in the first Fe layers. Above 800 K two adatom island species are present as the manifestation of an alloying process. The formation of an Fe–Nb surface alloy which in the submonolayer regime is interspersed with chains of pure Fe is suggested.