Solid-state1H NMR studies of different tungsten blue oxides and related substances

In situ HT‐XRD Study on the Formation of Hexagonal Ammonium Tungsten Bronze by Partial Reduction of Ammonium Paratungstate Tetrahydrate

“…The peak at δ = 4.9 ppm was assigned to the ammonium ions situated in the hexagonal channels, in accordance with ref. [5] We suppose that the peak at δ = 5.8 ppm is due to ammonia molecules in the hexagonal channels, an idea which is also supported by our XPS measurements and also by earlier results. [5] The peak at δ = 4.0 ppm may come from water molecules bound to the surface of or inside the bronze particles.…”

“…Furthermore, in our HATB sample, NH 3 molecules (N1s = 399.7 eV) were also detected in addition to NH 4 + ions (N1s = 401.9 eV). [50,51] Up to this time ammonia molecules were only detected in HATB by 1 H-MAS-NMR spectroscopy [4,5] whereas they were not detected by XPS. [32] Depth profiling by Ar + ion sputtering was not informative because sputtering distorted the structure so much that, due to oxygen loss, even W 0 species (W4f 7/2 = 32.5 eV and W4f 5/2 = 30.5 eV) appeared.…”

“…The slight difference in literature cell parameters [8,44,46] might have been caused mostly by the differences in the compositions of hexagonal ammonium tungsten bronze samples. [5] In order to obtain precise XRD data, we used all the simulated reflections of the P6 3 /mcm, no. 193 space group for finding and indexing the reflections in the measured XRD pattern of the HATB sample.…”

“…Since this peak was also present in the 1 H-MAS-NMR spectrum of the sample holder, we could not check the presence of OH groups on the surface of WO 3 and HATB particles. [4,5,57] Figure 4.…”

“…It is doped with K, Al and Si that ensure, after complete reduction in hydrogen, an overlapping crystallite structure of tungsten powder, which finally provides appropriate mechanical stability (a so-called "non-sag" feature) to tungsten filaments even at high operating temperatures in lamps. [1][2][3] Among the possible constituents of "tungsten blue oxide" (an X-ray amorphous phase, WO 3 , WO 2.9 , WO 2.72 , WO 2 and tungsten bronzes [1,2,[4][5][6][7] ), hexagonal ammonium tungsten bronze may have an important role in the doping process because of its ion-exchange property. [4,5,8,9] Furthermore, for applications in electrochromic devices, [1,[10][11][12][13][14] humidity [15,16] and gas sensors [17][18][19][20][21] as well as secondary batteries, [22] metastable tungsten oxides and oxide bronzes have attracted much attention in the past decades due to their open-tunnel structures.…”