Die Kristallstruktur von T-Nb₂O₅

Abstract

This modification of Nb2Os crystallizes in the space group Pbam with unit-cell dimensions a = 6" 175 (1), b= 29.175 (4) and c= 3.930 (1) A. The structure was determined and refined by the full-matrix leastsquares method based on 725 X-ray diffraction intensities collected on a four-circle diffractometer. The conventional R value is 0-054. The unit cell contains Nb16.aO42; Dx = 5-236 g cm-3. The 16 Nb atoms lie in a sheet parallel to (001) and are surrounded by seven or six oxygen atoms forming pentagonal bipyramidal or distorted octahedral coordination polyhedra respectively. These polyhedra are joined by edge-or corner-sharing within the (001) sheet and exclusively by corner-sharing along [001]. The remaining Nb atoms occupy those interstitial sites at random which lie between the (001) sheets of the other Nb atoms and are surrounded by nine oxygen atoms. The structure is similar to but not identical with that of fl-Ta2Os,

New Insights on the Oxidation of Unsaturated Fatty Acid Methyl Esters Catalyzed by Niobium(V) Oxide. A Study of the Catalyst Surface Reactivity

“…Catalysts 2018, 8,6 16 of 22 oxygen preferentially at C9 and C13, forming conjugated (more stable) peroxyl radicals i2(a) and i2(b) (Scheme 2). These radicals abstract a hydrogen atom from C11 in (I), regenerating i1 and forming hydroperoxides 7(a) and 7(b), which undergo a Hock-type rearrangement [80] catalyzed by the acidity of niobium oxide(V).…”

“…The most common phases are: amorphous [5], TT (pseudohexagonal or monoclinic geometry, obtained by heat treatment from 300 to 550 • C) [6,7], T (orthorhombic, from 550 to 850 • C) [8] and H (monoclinic, >1000 • C) [9].…”

Synthesis and Structural Properties of Niobium Pentoxide Powders: A Comparative Study of the Growth Process

“…A field emission scanning electron microscope (SEM Vega3 Tescan) operating at 5.0kV was used to verify the material morphology. To analyze the crystallite growth, the crystallite size (L) of the Nb 2 O 5 nanoparticles was calculated by the Scherrer's equation L = Kλ/(βcosθ), (for peak broadening due to size effects) where K is the shape correction factor, 0.9 for L taken as the volume-averaged crystallite dimension perpendicular to the hkl diffraction plane; λ is the wavelength used, θ is the Bragg diffraction angle measured hkl peak and β represents the FWHM (Full width at half maximum) measured in radians on the 2θ scale 22 Table 4 shows the results of specific surface area, S BET determined by taking data at relative pressures between 0.03 and 0.15. The method had accuracy constraints during the measurement process.…”

Mn-modification effects on Nb2O5 structural, optical and vibrational properties

“…Increasing the Mn concentration arises also peaks of low intensity. For x=0.1 and x=0.2 was found the structure orthorhombic [10] with space group Pbcn, corresponding to Manganese Niobium Oxide; it is believing that the Mn ions enter to Niobium pentoxide matrix occupying substitutional sites. Additional reflections consistent with Mn3O4 phase were observed, whose intensity depend on the annealing temperature.…”