Structure of P₂O₅–SiO₂ Pure Network Former Glasses Studied by Solid State NMR Spectroscopy

Abstract

The structure of binary (SiO 2 ) 100-x −(P 2 O 5 ) x glasses has been investigated by Raman scattering, 29 Si and 31 P magic angle spinning (MAS) as well as static 31 P NMR spectroscopy. 29 Si chemical shift trends reflect the successive replacement of Si−O−Si by Si−O−P linkages as the compositional parameter x is increased. While 31 P MAS NMR does not resolve separate phosphate species, the static 31 P NMR lineshapes were successfully simulated by considering the effect of uncorrelated distribution functions of the chemical shift tensor components upon the line shape. On the basis of these simulations, which were also found to be consistent with the experimental 31 P MAS NMR spectra, two distinct sites can be resolved: a dominant site characterized by an axially symmetric chemical shift tensor, assigned to P (3) units, and (only in the case of the x = 25 and 30 glasses) a Gaussian component reflecting phosphate species interacting with fiveand six-coordinated silicon species. For 0 ≤ x < 25, the decrease in average coordination number may provide the structural explanation for the strong decrease in the glass transition and liquidus temperatures over this composition range, whereas the subsequent increase in T g at higher P 2 O 5 contents is correlated with the appearance of the higher-coordinated silicon species. While these higher-coordinated silicon species occur within separate microdomains, 31 P spin echo decay spectroscopy suggests that the majority of P atoms tend to be randomly distributed in space, consistent with a statistical P−O−P, Si−O−P, and Si−O−Si connectivity distribution.

Potential Application of Perovskite Glass Material in Photocatalysis Field

“…Through the analysis of glass compositions, it can be seen that there are a variety of Br compounds (NaBr, CsBr, and PbBr 2 ) in the glass. Br peaks shift to the low binding energy with the increase of P content (Figure f), confirming that more CsBr is generated in the glass (binding energy: CsBr < PbBr 2 = NaBr), which corresponds to Figure d. In conclusion, with the increase of P 2 O 5 content, the looser glass network structure brings the high atomic mobility (Cs, Pb, and Br) and provides the foundation for nucleation of CsPbBr 3 QDs in the glass.…”

Structural origin of thermally induced refractive index changes in Yb3+/Al3+/P5+/F−‐co‐doped silica glass

“…Figure 5D depicts the 29 Si MAS NMR spectra of the investigated glasses. The spectrum of the pristine YbAPF0.85 glass shows a peak near −110 ppm, which is ascribed to the Q 4 units 30 . After thermal annealing, there is no obvious change in it, further demonstrating that the precipitated crystal is the AlPO 4 one.…”

“…The former is ascribed to the bending vibration of Al–O–P bonds 27, 28 . The latter originates from the summed contribution of the stretching vibrations in the Al–O–P, Al–O–Si, Si–O–Si, and P–O–Si bonds 29‐31 . Compared with those of the F300 glass, the D 1 and D 2 peaks of the YbAPF0.85 glass are weaker, suggesting the formation of the Si–O–Al, Si–O–P, and Si–F bonds with the breakage of the Si–O–Si ones in the YbAPF0.85 glass.…”

“…The spectrum of the pristine YbAPF0.85 glass shows a peak near −110 ppm, which is ascribed to the Q 4 units. 30 After thermal annealing, there is no obvious change in it, further demonstrating that the precipitated crystal is the AlPO 4 one. After fire polishing, this signal slightly shifts to a higher frequency, as shown in Table 4.…”

“…27,28 The latter originates from the summed contribution of the stretching vibrations in the Al-O-P, Al-O-Si, Si-O-Si, and P-O-Si bonds. [29][30][31] Compared with those of the F300 glass, the D 1 and D 2 peaks of the YbAPF0.85 glass are weaker, suggesting the formation of the Si-O-Al, Si-O-P, and Si-F bonds with the breakage of the Si-O-Si ones in the YbAPF0.85 glass. After thermal annealing, the D 1 and D 2 peak areas in the F300 and YbAPF0.85 glasses slightly decreased, and they increased after fire polishing.…”