Effect of processing method on physical properties of Nb2O5 (original) (raw)
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Sol–gel synthesis and characterization of Nb2O5 powders
Materials Letters, 2004
Nb 2 O 5 powders were prepared by the sol -gel procedure. Nb(OC 2 H 5 ) 5 dissolved in ethanol was (a) rapidly hydrolysed by adding a concentrated NH 4 OH solution, or (b) slowly hydrolysed by adding a small amount of H 2 O. The Nb 2 O 5 powders were characterized by XRD, DTA/TGA, FT-IR spectroscopy and SEM. The initial Nb 2 O 5 powders were amorphous. Upon heating at 300 jC of the amorphous powder obtained by the method (a) there was no change as shown by XRD, whereas the amorphous powder obtained by the method (b) and also heated at 300 jC contained Nb 2 O 5 (TT-phase) plus an amorphous fraction. The amorphous powders heated at 500 jC contained Nb 2 O 5 (TT-phase), whereas at 650 jC the Nb 2 O 5 (T-phase) was obtained. Crystallite sizes were determined using the Scherrer method. The agreggates of nanosized Nb 2 O 5 were present in amorphous Nb 2 O 5 precursors and upon their heating at 300 jC, whereas upon heating at 650 jC a porous interconnected microstructure was formed in both preparations, (a) and (b), as shown by SEM. D
Nb2O5 thin films were deposited onto heated glass substrates by RF magnetron sputtering using a Nb2O5 target. The films were annealed in air at temperatures between 400 and 700 C for 6 h. Effects of the crystalline structure on optical, structural, electrochromic and bonding properties of the Nb2O5 thin films were investigated by X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, optical spectrophotometry and electrochemical measurements. The film refractive index varied between 2.09 and 2.22 at the wavelength of 550 nm depending on the annealing temperature. The decrease of the optical band gap revealed for the films with increasing annealing temperature is attributed to oxygen-ion vacancies in the film structure. The orthorhombic structure of Nb2O5 films resulted in good electrochromic properties with high colouration efficiencies of 19.56 cm2/C and 53.24 cm2/C at 550 nm and 1000 nm, respectively. The optical, structural and electrochromic properties of the different crystalline polymorphic forms of the Nb2O5 films make them attractive for optical applications.
Multi-Photonic behavior of Nb2O5 and its correlation with synthetic methods
Journal of Materials Science, 2021
The performance of niobium pentoxide (Nb 2 O 5) as photoanodes in dye-sensitized solar cells (DSSCs) and as catalysts in the photocatalytic degradation of Rhodamine B (RhB) was investigated. Four samples of Nb 2 O 5 (Nb 2 O 5 _SG, Nb 2 O 5 _CR, Nb 2 O 5 _PP, and Nb 2 O 5 _MA) were synthesized by four different methods, respectively, entailing the sol-gel, combustion, polymeric precursors, and a microwave-assisted hydrothermal reaction. In all these samples, the orthorhombic phase of Nb 2 O 5 was obtained, which resulted in different shapes and assemblies, which is very relevant because the surface area, shape, and size distribution of the nanoparticles significantly contribute to the optical process. The bandgap remained constant at 3.0 eV for all the samples, even for the sample prepared by the combustion method. An additional phase, which is related to local distortions, was revealed by Raman spectroscopy within the vibration range of 688-260 cm-1. DSSCs using photoanodes with smaller and more dispersed Nb 2 O 5 particles showed better results than those with inhomogeneities. For comparison, DSSCs were assembled using two different counter electrodes, platinum and graphite. The DSSC with platinum showed better photovoltaic results, mainly with photocurrents from 1.17 mA.cm-2 for Nb 2 O 5 _CR to 1.64 mA.cm-2 for Nb 2 O 5 _SG. The same trend was observed for the photocatalytic degradation of RhB, where the smaller and dispersed particles of Nb 2 O 5 _CR and Nb 2 O 5 _SG exhibited the best performance and, respectively, degraded approximately 75% and 61% of the RhB dye over 180 min. Therefore, the results of this study established a correlation between the synthesis methods and photonic behavior.
Influence of Nb2O5 on the optical band gap and electrical
Glass system xNb 2 O 5 ·(30-x)BaO·70B 2 O 3 (0 ≤ x ≤ 12, mol%) has been prepared using normal melt-quench technique (1473K, 1h). In the present work the influence of Nb 2 O 5 on density, molar volume, optical band gap and electrical conductivity of barium borate glasses has been reported. The density and molar volume increases with increasing concentration of Nb 2 O 5 . Increase in V M indicates that the volume of non-bridging oxygens (NBOs) sites produced by Nb 2 O 5 is greater than that produced by BaO in the present glasses. The optical band gap energy (E g ) has been calculated from the Tauc's plots for both direct and indirect transitions. The decrease in E g with increase in Nb 2 O 5 content is again due to increasing concentration of the NBO ions which results in the shifting of valence band maximum (VBM) to higher energies. The value of Urbach energy (ΔE) is in the range 0.16-0.22 eV for all the glasses. The dc electrical conductivity has been measured in the temperature range 300K to 623K and is found to increase with increasing temperature. The increase in conductivity with increase in Nb 2 O 5 content in these glasses indicates the presence of NbO 6 units.
2009 1 Influence of Nb2O5 on the optical band gap and electrical
Glass system xNb 2 O 5 ·(30-x)BaO·70B 2 O 3 (0 ≤ x ≤ 12, mol%) has been prepared using normal melt-quench technique (1473K, 1h). In the present work the influence of Nb 2 O 5 on density, molar volume, optical band gap and electrical conductivity of barium borate glasses has been reported. The density and molar volume increases with increasing concentration of Nb 2 O 5 . Increase in V M indicates that the volume of non-bridging oxygens (NBOs) sites produced by Nb 2 O 5 is greater than that produced by BaO in the present glasses. The optical band gap energy (E g ) has been calculated from the Tauc's plots for both direct and indirect transitions. The decrease in E g with increase in Nb 2 O 5 content is again due to increasing concentration of the NBO ions which results in the shifting of valence band maximum (VBM) to higher energies. The value of Urbach energy (ΔE) is in the range 0.16-0.22 eV for all the glasses. The dc electrical conductivity has been measured in the temperature range 300K to 623K and is found to increase with increasing temperature. The increase in conductivity with increase in Nb 2 O 5 content in these glasses indicates the presence of NbO 6 units.
Influence of Nb2O5 on the optical band gap and electrical conductivity of Nb2O5·BaO·B2O3
Iop Conference Series: Materials Science and Engineering, 2009
Glass system xNb 2 O 5 ·(30-x)BaO·70B 2 O 3 (0 ≤ x ≤ 12, mol%) has been prepared using normal melt-quench technique (1473K, 1h). In the present work the influence of Nb 2 O 5 on density, molar volume, optical band gap and electrical conductivity of barium borate glasses has been reported. The density and molar volume increases with increasing concentration of Nb 2 O 5 . Increase in V M indicates that the volume of non-bridging oxygens (NBOs) sites produced by Nb 2 O 5 is greater than that produced by BaO in the present glasses. The optical band gap energy (E g ) has been calculated from the Tauc's plots for both direct and indirect transitions. The decrease in E g with increase in Nb 2 O 5 content is again due to increasing concentration of the NBO ions which results in the shifting of valence band maximum (VBM) to higher energies. The value of Urbach energy (ΔE) is in the range 0.16-0.22 eV for all the glasses. The dc electrical conductivity has been measured in the temperature range 300K to 623K and is found to increase with increasing temperature. The increase in conductivity with increase in Nb 2 O 5 content in these glasses indicates the presence of NbO 6 units.
The Influence of Thermal Treatment on the Electronic Properties of a-Nb2O5
ECS Transactions, 2009
The effect of thermal treatment for lh at 250°C in air or under vacuum on the electronic structure of thick amorphous anodic niobia was characterized by electrochemical impedance, differential admittance (DA) and photocurrent spectroscopy (PCS). The analysis of anodized niobia has
2013 - Nb2O5 nanosize powders prepared by sol–gel – Structure, morphology.pdf
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Nanoscale Research Letters, 2006
The reaction of pentaethoxy niobate, Nb(OEt)5, at elevated temperature (800 °C) under autogenic pressure provides a chemical route to niobium oxide nanorods coated with amorphous carbon. This synthetic approach yielded nanocrystalline particles of Nb2O5@C. As prepared Nb2O5@C core-shell nanorods is annealed under air at 500 °C for 3 h (removing the carbon coating) results in neat Nb2O5nanorods. According to the TEM measurements, the Nb2O5crystals exhibit particle sizes between 25 nm and 100 nm, and the Nb2O5crystals display rod-like shapes without any indication of an amorphous character. The optical band gap of the Nb2O5nanorods was determined by diffuse reflectance spectroscopy (DRS) and was found to be 3.8 eV.