Effect Of Niobium Doping Research Articles

Wettability of anatase TiO2 surface: Effect of niobium doping

The effect of niobium doping on the hydrophilic behavior of anatase TiO2 surface was demonstrated on a series of x-Nb-TiO2 nanocoatings with dopant concentrations in the range of 0.0 - 1.0 at.% Nb. Thin films prepared on glass substrates from sols by dip-coating were characterized by tensiometric, work function and isoelectric point measurements along with FT-IR spectroscopy in situ method. Using macroscopic and microscopic techniques, it was found that, at low doping level, it is the functionalization of the anatase surface with niobium ions that leads to a drastic change in its surface acid-base as well as electronic properties and, as a consequence, to a sharp increase in the initial surface hydrophilicity. The rearrangement in the hydroxyl‑hydrated layer with the formation of additional hydroxyl groups as a result of surface functionalization has an increased effect on wettability only at low levels of niobium inclusion, whereas with increasing dopant content the electronic factor plays a significant role on the properties of titanium dioxide, including its wettability. The kinetic dependencies of the photoinduced superhydrophilic conversion for all Nb-doped titanium dioxide surfaces were obtained and discussed in terms of proposed mechanism. Both the initial hydrophilic state and the initial rate of photoinduced hydrophilic conversion depend on the Nb concentration in titanium dioxide, while the final UV-induced superhydrophilic state is achieved for all Nb-doped TiO2 regardless of the dopant content.

Effect of niobium doping on excitonic dynamics in MoSe2

Transition metal dichalcogenides (TMDs) have emerged as attractive two-dimensional semiconductors for future electronic and optoelectronic applications. Their charge transport properties, such as conductivity and the type of charge carriers, can be effectively controlled by substitutional doping of the transition metal atoms. However, the effects of doping on the excitonic properties, particularly their dynamical properties, have been less studied. Using Nb-doped MoSe2 as a case study, we experimentally investigate the effect of doping on excitonic dynamics in TMDs. Transient absorption measurements are used to directly compare the dynamical properties of excitons in Nb-doped MoSe2 across monolayer, bilayer, and bulk flakes with their undoped counterparts. The exciton lifetimes in Nb-doped flakes are significantly shorter than those in their undoped counterparts. This effect is attributed to the trapping of excitons in defect states introduced by Nb impurities. These results reveal an important consequence of Nb doping on excitonic dynamics in TMDs.

The effect of niobium doping on the corrosion resistance of stainless steel coatings

The effect of niobium doping on the corrosion resistance of stainless steel coatings

Effect of Niobium Doping on Structural Stability and Electrochemical Properties of LiNiO2 Cathode for Li-Ion Batteries

LiNiO2, a promising cobalt-free cathode, suffers from poor cyclic stability and inferior rate performance due to structural degradation. A strategy based on the synergistic effect of a strong Nb–O bond (753 kJ mol−1), high valence state (Nb5+), and larger ionic radius (0.64 Å) was developed to improve the properties of LiNiO2. The synergistic effects can effectively improve lattice stability, lower Li+/Ni2+ cation mixing, expand LiO6-slab spaces, enhance the conductivity and inhibit the H2–H3 phase transition, which can enhance the stability of the layered structure, accelerate Li+ diffusion and alleviate mechanical damage. Therefore, LiN0.99Nb0.01O2 exhibits higher capacity retention (91.4% after 100 cycles at 0.5C) and superior rate capability (143 mAh g−1 at 5C). As a comparison, the data of bare LiNiO2 is 69.2% and 127 mAh g−1 under the same conditions. These results further demonstrate the effectiveness of the proposed doping strategy.

The effect of niobium doping on lithium manganese oxide surfaces, LiMn2-xNbxO4: DFT study

Lithium manganese oxide (LiMn2O4) is one of the promising cathode material for lithium-ion batteries (LIBs), however, it suffers from capacity fading mainly due to surface manganese (Mn2+) ion dissolution during Charge/discharge processes. Although many studies focused on reducing Mn-dissolution, surface modification has proven to be an ideal method of reducing Mn2+ ion dissolution in secondary Li-ion batteries. In this study, the density functional theory calculations were carried out to study the bulk properties and investigate the effect of Nb surface doping on major LiMn2O4 spinel surfaces. Upon surface Nb doping, we observed a decrease in surface free energy as compared to the surface energies of pure surfaces, indicating that the surface stabilizes upon doping. However, the (001) surface remained the most stable facet, with a similar trend of increasing energies and decreasing stability, i.e. (001) < (011) < (111). Due to the stronger binding energy of Nb-O as compared to Mn-O, doping with Nb can suppress the Mn dissolution during intercalation and hence improve the electrochemical performance.

Effects of niobium doping on the stability of SrCo0.2Fe0.8O3-δ cathodes for intermediate temperature solid oxide fuel cells

Effects of Nb-doping on the stability and electrochemical performance of SrCo0.2Fe0.8O3-δ were studied. Electrochemical impedance spectroscopy and electrical conductivity measurements show that SrCo0.2Fe0.7Nb0.1O3-δ cathode has excellent electrochemical performance, while further Nb-doping reduces the performance of cathodes. Microstructure evolution reveals that Nb-doping suppresses the formation of impurity particles on the surface of cathodes. Good chemical compatibility between SrCo0.2Fe0.8-yNbyO3-δ with GDC powders is confirmed by X-ray powder diffraction measurements. Results of temperature programmed desorption, thermogravimetric and thermal expansion coefficients tests indicate that Nb-doping improves the structural and chemical stability of SrCo0.2Fe0.8O3-δ cathodes because of the decrease of the concentration of oxygen vacancies in the crystal lattices.

Effect of niobium doping on the dielectric and nonlinear current–voltage characteristics of [formula omitted] ceramics

The effect of Nb5+ on the crystallographic structure, electrical properties and the dielectric behaviour of Na0.5La0.5Cu3Ti(4−x)NbxO12 ceramics prepared via the solid-state reaction method were investigated. Rietveld refinement of the powder diffraction data confirmed a cubic, single phase structure with space group Im3. A low frequency Debye-type relaxation is observed for the Nb-doped samples in addition to the usually observed high frequency relaxation. The grain boundary resistance decreased significantly with increasing Nb5+ dopant. The reduced grain boundary resistivity was found to be responsible for the decrease in the potential barrier at the grain boundary as observed from the overall variation of current density-electric field (J–E) characteristics. The dielectric constant at low Frequency is increased with increasing Nb content. The dielectric behaviour of the compound is explained on the basis of the Internal Barrier Layer Capacitance (IBLC) model.

Effect of Niobium Doping on Electrochemical Properties of Microwave Synthesized Carbon Coated Nanolithium Iron Phosphate for High Rate Underwater Applications

Lithium iron phosphate (LiFePO4) for lithium-ion batteries is considered as perfect cathode material for various military applications, especially underwater combat vehicles. For deployment at high rate applications, the low conductivity of LiFePO4 needs to be improved. Cationic substitution of niobium in the native carbon coated LiFePO4 is one of the methods to enhance the conductivity. In the present work, how the niobium doped solid solution could be formed is studied. Nanopowders of LiFePO4/C and Li1−xNbxFePO4/C (x = 0.05, 0.1, 0.15, 0.16) are synthesized from precursors using microwave synthesis. The solid solution formation up to (x = 0.15) Li1−xNbxFePO4/C without impurity phases is confirmed by X-ray diffraction (XRD) pattern and Fourier transform infrared spectroscopic (FTIR) results. Particle distribution is obtained by scanning electron microscope from the synthesized powders. Energy dispersive X-ray spectrometer (EDS) results qualitatively confirmed the presence of niobium. Also, direct current (dc) conductivities are measured using sintered pellets and activation energies are calculated using Arrhenius equation. The dependence of conductivity and activation energy of LiFePO4/C on variation of niobium doping is investigated in this study. CR2032 type coin cells are fabricated with the synthesized materials and subjected to cyclic voltammetry studies, rate capability and cycle life studies. Diffusion coefficients are obtained from electrochemical impedance spectroscopy studies. It is observed that room temperature dc conductivity improved by niobium doping when compared to LiFePO4/C (0.379 × 10−2 S/cm) and is maximum for Li0.9Nb0.1FePO4/C (40.58 × 10−2 S/cm). It is also observed that diffusion coefficient of Li+ in Li0.9Nb0.1FePO4/C (13.306 × 10−9 cm2 s−1) improved by two orders of magnitude in comparison with the pure LiFePO4 (10 − 12 cm2 s−1) and carbon-coated nano LiFePO4/C (0.632 × 10−11 cm2 s−1). Cells with Li0.9Nb0.1FePO4/C are able to deliver useful capacity of around 104 mAh/g at 10 C rate. More than 500 cycles are achieved with Li0.9Nb0.1FePO4/C at 20 C rate.

Effect of niobium doping on the structural, electrical and optical properties of epitaxial SnO2 films on MgF2 (110) substrates by MOCVD

Niobium (Nb)-doped SnO2 films were epitaxially grown on MgF2 (110) substrates by the metal organic chemical vapor deposition (MOCVD) technique. Structural, electrical and optical properties of the obtained films with different Nb-doping levels were investigated. The X-ray diffraction analysis revealed that the obtained films were rutile structure SnO2 grown along the (110) orientation. The epitaxial relationship between the Nb-doped SnO2 film and MgF2 substrate was clarified as SnO2 (110) || MgF2 (110) with SnO2 [001] || MgF2 [001] by the interface selected area electron diffraction measurement. A Hall mobility as high as 84 cm2 V−1 s−1 with the lowest resistivity of 2.9 × 10−3 Ω cm were obtained for the 4.3 at.% Nb-doped SnO2 film. The average optical transmittance in visible range of the 4.3 at.% Nb-doped SnO2 film exceeded 80% and the optical band gap was about 4.04 eV.

Effect of niobium doping on the structure and electrochemical performance of LiNi0.5Co0.2Mn0.3O2 cathode materials for lithium ion batteries

Key issues including poor rate capability and limited cycle life span should be addressed for the extended application of LiNi0.5Co0.2Mn0.3O2 cathode. The suppressed Li+/Ni2+ site exchange, enlarged LiO2 inter-slab space and reduced impedance, which could facilitate the structure stability, were achieved by controlled Niobium (Nb) doping and contributed to enhanced performance even at elevated temperature (55°C). The detailed role of the doped Nb was investigated thoroughly and systematically with the help of XRD, SEM, XPS and related electrochemical tests. The full and accurate results demonstrate that the Li(Ni0.5Co0.2Mn0.3)0.99Nb0.01O2 sample with appropriate Nb doping amount possess high capacity retention of 93.77% after 100 cycles at 1.0C and improved rate performance with 125.5mAhg−1 at 5.0C, which are much better than that of the LiNi0.5Co0.2Mn0.3O2. Moreover, at high temperature of 55°C, Nb doping shows more remarkable effect on stabilizing the structure and 88.63% of the initial reversible capacity could be retained, which is ~20% higher than the LiNi0.5Co0.2Mn0.3O2. This study intensively determines that controlled Nb doping could be effectively maintain the structure stability of advanced LiNi0.5Co0.2Mn0.3O2 cathode and promote the development of high energy density lithium ion batteries.

Effect of Niobium Doping on the Properties of Yttria-Stabilised Zirconia for Solid Electrolyte in Solid Oxide Fuel Cell

8 mol % Yttria Stabillize Zirconia (8YSZ) generally used as solid electrolyte in solid oxide fuel cell (SOFC). In this study, niobium (0, 1, 2, 3 mol%) doped 8YSZ ceramics were prepared by the conventional solid state process. The mixtures of powders were calcined, compacted into cylinderical pellets, and sintered at 1500°C for 2 hours in air atmosphere. All samples were evaluated for phase stability, microstructure and electrical conductivity. Tetragonal phase was detected as the major phase for all studied samples. With increasing in Nb addition, tetragonal and cubic phase started to transform to monoclinic phase. The introduction of Nb2O5 (more than 0.5 mol %) was not only useful to enhance the densification, but also helpful to enhanced the ionic conductivity of 8YSZ samples. SEM micrographs of niobium-doped zirconia powders indicated the coalesce of fine particles with sizes varying from 10 μm to 1 μm, in response to increasing in Nb content.

The Effect of Niobium Doping on the Electrical Properties of 0.4(Bi0.5K0.5)TiO₃-0.6BiFeO₃ Lead-Free Piezoelectric Ceramics.

Ceramics in the system (Bi0.5K0.5)TiO3-BiFeO3 have good electromechanical properties and temperature stability. However, the high conductivity inherent in BiFeO3-based ceramics complicates measurement of the ferroelectric properties. In the present work, doping with niobium (Nb) is carried out to reduce the conductivity of (Bi0.5K0.5)TiO3-BiFeO3. Powders of composition 0.4(K0.5Bi0.5)Ti1−xNbxO3-0.6BiFe1−xNbxO3 (x = 0, 0.01 and 0.03) are prepared by the mixed oxide method and sintered at 1050 °C for 1 h. The effect of Nb doping on the structure is examined by X-ray diffraction. The microstructure is examined by scanning electron microscopy. The variation in relative permittivity with temperature is measured using an impedance analyzer. Ferroelectric properties are measured at room temperature using a Sawyer Tower circuit. Piezoelectric properties are measured using a d33 meter and a contact type displacement sensor. All the samples have high density, a rhombohedral unit cell and equiaxed, micron-sized grains. All the samples show relaxor-like behavior. Nb doping causes a reduction in conductivity by one to two orders of magnitude at 200 °C. The samples have narrow P-E loops reminiscent of a linear dielectric. The samples all possess bipolar butterfly S-E loops characteristic of a classic ferroelectric material. Nb doping causes a decrease in d33 and Smax/Emax.

Anomalous behavior of B1g mode in highly transparent anatase nano-crystalline Nb-doped Titanium Dioxide (NTO) thin films

The effect of Niobium doping and size of crystallites on highly transparent nano-crystalline Niobium doped Titanium Dioxide (NTO) thin films with stable anatase phase are reported. The Nb doping concentration is varied within the solubility limit in TiO2 lattice. Films were annealed in controlled environment for improving the crystallinity and size of crystallites. Elemental and thickness analysis were carried out using Rutherford backscattering spectrometry and cross sectional field emission scanning electron microscopy. Structural characteristics reveal a substitutional incorporation of Nb+5 in the TiO2 lattice which inhibits the anatase crystallites growth with increasing the doping percentage. The micro-Raman (MR) spectra of films with small size crystallites shows stiffening of about 4 cm−1 for the Eg(1) mode and is ascribed to phonon confinement and non-stoichiometry. In contrast, B1g mode exhibits a large anomalous softening of 20 cm−1 with asymmetrical broadening; which was not reported for the case of pure TiO2 crystallites. This anomalous behaviour is explained by contraction of the apical Ti-O bonds at the surface upon substitutional Nb5+ doping induced reduction of Ti4+ ions also known as hetero-coordination effect. The proposed hypotheses is manifested through studying the electronic structure and phonon dynamics by performing the near edge x-ray absorption fine structure (NEXAFS) and temperature dependent MR down to liquid nitrogen temperature on pure and 2.5 at.% doped NTO films, respectively.

Suppression of Anatase to Rutile Phase Transformation of Niobium doped TiO2 Synthesized by High Temperature Diffusion Technique

The effects of niobium doping (for doping concentrations: 0.02 – 0.06 at. % Nb5+) on the crystal structure of TiO2 prepared by high temperature diffusion method were investigated. The samples were characterized using energy dispersive X-ray fluorescence (EDXRF) and X- ray diffraction (XRD) spectroscopy to investigate the chemical compositions, phase compositions and crystallinity of the thin films respectively. Despite the expected high reutilization at high temperatures (>600oC), XRD results confirmed a significant suppression of anatase to rutile phase transformation at even a higher synthesis (850oC) temperature. Grain growth retardation was also observed in niobium doped TiO2, results which were attributed to Nb5+ substitution of lattice Ti4+.

Effect of niobium doping on opto-electronic properties of sol–gel based nanostructured indium tin oxide thin films

Abstract Optically transparent conducting niobium-doped indium tin oxide (ITNO) thin films were deposited on soda lime glass via sol–gel spin coating technique under various Nb-doping contents. The effect of different Nb-dopant contents on the opto-electronic as well as microstructural properties of the films were characterized by means of UV–vis spectroscopy, four point probe, X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and atomic force microscopy (AFM). For this purpose, addition of different Nb contents with tin at fixed 6 at% is considered as the first approach. For the second and third approaches, different Nb-doping contents were added at fixed atomic ratios of In:Sn=94:6 and In:Sn=95:5, respectively. Optimum opto-electronic properties, including minimum resistivity of 37.2×10 −3 Ω cm with average transmittance of about 85% in the visible region and band gap of 3.48 eV was achieved for ITNO thin films prepared by the first approach at Nb and Sn doping content of 1 and 5 at%, respectively. XRD analysis revealed patterns of cubic bixbyite structure of In 2 O 3 and rhombohedral structure of ITO for Nb-doped films with small shift in major peak position to lower diffraction angles with the addition of Nb. FESEM micrographs show that addition of Nb causes clustering of the grains at higher doping content. However, AFM studies show that addition of Nb dopant leads to the formation of films with compact surface and less average roughness compare to the undoped ITO films.

Effect of Nb doping on structural, optical and photocatalytic properties of flame-made TiO2 nanopowder

TiO(2):Nb nanopowders within a dopant concentration in the range of 0.1-15at.% were prepared by one-step flame spray synthesis. Effect of niobium doping on structural, optical and photocatalytic properties of titanium dioxide nanopowders was studied. Morphology and structure were investigated by means of Brunauer-Emmett-Teller isotherm, X-ray diffraction and transmission electron microscopy. Diffuse reflectance and the resulting band gap energy were determined by diffuse reflectance spectroscopy. Photocatalytic activity of the investigated nanopowders was revised for the photodecomposition of methylene blue (MB), methyl orange (MO) and 4-chlorophenol under UVA and VIS light irradiation. Commercial TiO(2)-P25 nanopowder was used as a reference. The specific surface area of the powders was ranging from 42.9m(2)/g for TiO(2):0.1at.% Nb to 90.0m(2)/g for TiO(2):15at.% Nb. TiO(2):Nb particles were nanosized, spherically shaped and polycrystalline. Anatase was the predominant phase in all samples. The anatase-related transition was at 3.31eV and rutile-related one at 3.14eV. TiO(2):Nb nanopowders exhibited additional absorption in the visible range. In comparison to TiO(2)-P25, improved photocatalytic activity of TiO(2):Nb was observed for the degradation of MB and MO under both UVA and VIS irradiation, where low doping level (Nb < 1at.%) was the most effective. Niobium doping affected structural, optical and photocatalytic properties of TiO(2). Low dopant level enhanced photocatalytic performance under UVA and VIS irradiation. Therefore, TiO(2):Nb (Nb < 1at.%) can be proposed as an efficient selective solar light photocatalyst.

Effect of niobium doping on the optical and electrical properties in titanium dioxide grown by pulsed laser deposition

The influence of niobium (Nb) on both the electrical and optical properties in titanium dioxide (TiO2) grown by pulsed laser deposition was investigated. Nb atoms with a critical doping ratio of 8 at. % were carefully controlled in a 100 nm-thick TiO2 layer (Nb:TiO2). The Hall effect results revealed that the electrical resistivity and electron concentration of the resulting Nb:TiO2 film were 30 times lower and 2 orders of magnitude higher than those of un-doped TiO2 (u-TiO2), respectively, leading to a slight degradation of optical transmittance in the visible region. The room temperature photoluminescence results showed that the emission intensity at the near band of Nb:TiO2 was greatly enhanced, while, that at the impurity band created by oxygen vacancy (Vo) was almost constant. Detailed investigation of the T-dependent conductivity indicated that the Nb:TiO2 film possessed an activation energy as shallow as 20.8 meV, which suggested that the electrical properties were dominantly determined by Nb shallow impurity rather than point defects such as Vo.

Electrical properties of niobium doped barium bismuth-titanate ceramics

BaBi4Ti4–5/4xNbxO15 (BBNTx, x=0, 0.05, 0.15, 0.30) ceramics have been prepared by solid state method. XRD data indicate the formation of single-phase-layered perovskites for all compositions. SEM micrographs suggest that the grain size decreases with Nb doping. The effect of niobium doping on the dielectric and relaxor behavior of BaBi4Ti4O15 ceramics was investigated in a wide range of temperatures (20–777°C) and frequencies (1.21kHz to 1MHz). Nb doping influences Tc decrease as well as the decrease of dielectric permittivity at Curie temperature. At room temperature, undoped BaBi4Ti4O15 exhibits dielectric constant of ∼204 at 100kHz, that slightly increases with Nb doping. The conductivity of BBNT5 ceramics is found to be lower than that of other investigated compositions. The value of activation energy of σDC was found to be 0.89eV, 1.01eV, 0.93eV and 0.71eV for BBT, BBNT5, BBNT15 and BBNT30, respectively.

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of niobium doped anatase; effect of niobium on the conductivity and photocatalytic activity

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) was used to synthesise anatase thin-films with gradating substitutionally doped niobium content on a single film. This is the first time such a combinatorial system has been formed by CVD or other means. The film was characterised via X-ray diffraction (XRD) mapping, Raman spectroscopy, atomic force microscopy (AFM), wavelength dispersive X-ray analysis (WDX) and X-ray photoelectron spectroscopy (XPS) analysis. Film thicknesses and band-gap energies were derived from Swanepoel thickness analysis and Tauc plots of transmittance spectra. Water droplet contact angle measurements displayed a UVC induced movement to super hydrophilic behaviour by a photo-induced superhydrophilicity (PSH) mechanism, irrespective of niobium levels. The film's conductivity and photocatalytic activity to different light sources were mapped using a four-point probe and novel flat-bed digital scanning technique. This allowed for the systematic investigation on the effect of niobium doping. It was found that film growth rate in addition to niobium concentration directly influenced photocatalytic activity and electrical conductivity. A direct relationship between conductivity of these Nb-doped anatase thin-films and photocatalytic activity to both UVA and indoor lighting was also observed. Films synthesized by the cAPCVD route analysed in conjunction with mapping analysis tools provide a shortcut to investigating the effect of metal dopant on the functional properties for a wide range of phase space on a single film, enabling rapid analysis.

Effects of Niobium Doping on Dielectric and Ferroelectric Properties of Chromium Modified Lead Zirconate Titanate Ceramics

Effects of niobium doping on dielectric and ferroelectric properties of unmodified lead zirconate titanate (PZT) and chromium modified lead zirconate titanate (Cr-modified PZT) have been investigated. The x-ray structural study shows the phase formed depending on the dopant concentrations with increasing the doping content tending to an increase in the rhombohedral phase in both of PZT and Cr-modified PZT ceramics. Furthermore, the Curie temperature (T c ) and dielectric constant are decreased with increasing Nb concentration and the dielectric loss of Cr-modified PZT ceramics is lower than that of the PZT ceramics. From the hysteresis loop measurements, by increasing Nb concentration, the unmodified PZT ceramics show increase in the coercive field, while the remnant polarization decreases slightly. However, coercive field decreases, and the remanent polarization tends to increase with increasing niobium concentration from 1-3 mol% in Cr-modified PZT ceramics. Further increase in niobium concentration results in a drop of the remanent polarization and the coercive field.