Niobium-based Oxides Research Articles

Electronic Band Structure of Exfoliated Titanium- and/or Niobium-Based Oxide Nanosheets Probed by Electrochemical and Photoelectrochemical Measurements

Exfoliated two-dimensional (2D) unilamellar nanosheets of Ca2Nb3O10–, TiNbO5–, Ti2NbO7–, and Ti5NbO143– were deposited layer-by-layer to produce multilayer films on indium–tin–oxide (ITO)-coated glass electrodes, and their electrochemical and photoelectrochemical properties were explored. The layer-by-layer assembly process via sequential adsorption with counter polycations was monitored by UV–visible absorption spectra and X-ray diffraction measurements, which confirmed the successful growth of films, where nanosheets and polycations are alternately stacked at a separation of 1.6–2.4 nm. Exposure to UV light totally removed polycations, producing inorganic films. Cyclic voltammetry on Ti and/or Nb oxide nanosheet electrodes thus fabricated showed reduction/oxidation (Ti3+/Ti4+ and Nb4+/Nb5+) peaks associated with insertion/extraction of Li+ ions into/from intersheet galleries of the films. The extent of the redox reaction is found to be governed by the cation density in the nanosheet gallery. Anodic phot...

Development of bioactive materials based on bone-bonding mechanism on metal oxides

Bioactive ceramics have high biological affinity that enables direct bone-bonding. However they do not have mechanical performances enough to repair bone tissue under loaded conditions. It has been revealed that most materials exhibiting bioactivity form bone-like apatite in body environment. We investigated apatite-forming ability of tantalum- and niobium-based oxide gels in simulated body environment in order to fundamentally clarify chemical structure effective for achieving bioactivity. We found that Ta-OH and Nb-OH groups on the surfaces of the oxide gels have a potential to form the apatite. On the basis of these findings, we have successfully provided tough tantalum metal with bioactivity by simple NaOH and heat treatments that form a lot of Ta-OH groups on their surfaces. We also synthesized bioactive organic-inorganic hybrids with flexibility by organic modification of inorganic chemical species with apatite-forming ability. A sequence of material design described above would produce bioactive materials with various mechanical properties.

Pressure-induced metal–insulator transition in orthorhombic Nb 12O 29

In orthorhombic Nb 12O 29 reported as the first example of a magnetically ordered ( T N = 12 K ) system in niobium-based oxides, the metallic conduction even below T N suggests that Nb 12O 29 could be an itinerant antiferromagnet. In order to investigate the pressure effects on these novel magnetic and metallic behaviors, we have carried out resistivity measurements up to 2.5 GPa. The resistivity–temperature curves show metallic behavior below P c ∼ 1 GPa . On the other hand, when pressure is applied over ∼1 GPa, the resistivity increases with decreasing temperature from 300 K. These results indicate metal–insulator (MI) transition at P c ∼ 1 GPa . We will discuss the origin of the MI transition in Nb 12O 29 in terms of charge ordering and pressure-induced amorphization as have been suggested in other niobium oxides.

Application of Nb-O Affinity in Clean Steel

This report introduces a new deoxidation process that starts with a vacuum degassing followed by the addition of ferro-niobium in the same vacuum facility. The addition of strong deoxidation substance like aluminum and/or silicon is not adopted. Owing to the degassing in vacuum, which in reality reacts as deoxidation with C in molten steel, the solute oxygen in molten steel (O) is stabilized by niobium, which generates an ample number of fine oxide particles composed of (Nb, Mn)2O3-phase. Provided the carbon-degassing is conducted so as to reach the O prior to the FeNb addition would be around 100ppm and less, these oxide-inclusions do not agglomerate before and during solidification, because of the weak cohesivity of niobium-based oxides in molten steel, which would enable defect-free cast products as well as clogging-less casting operation. Also, the steel containing these fine (Nb, Mn)2O3-particles but no Al, exhibits so-called intra-granular acicular ferrite transformation and good toughness of weld heat affected zone (HAZ).

Synthesis and physical properties of niobium-based oxide, Sr 2− xLa xNbO 4 (0⩽ x

Structural and physical properties of Sr 2− x La x NbO 4− δ (0⩽ x<0.2) with ordered-perovskite structure were investigated. Powder X-ray diffraction analysis showed that the samples with 0⩽ x⩽0.1 were of nearly single phase. For all the samples, electrical resistivity ( ρ) exhibited semiconducting behavior at temperatures below 310 K. On the basis of the Arrhenius plots in the temperature range between 150 and 310 K, the activation energies ( E a) were estimated at E a∼0.17 eV. The sign of thermoelectric power coefficient ( S) was confirmed to be negative for all the samples below 310 K, indicating that the dominant charge carriers were most likely electrons.