Structure of P2O5-SiO2 pure network former glasses studied by solid state NMR spectroscopy.
OLIVEIRA JR., Marcos de; AITKEN, Bruce; ECKERT, Hellmut.
OLIVEIRA JR., Marcos de; AITKEN, Bruce; ECKERT, Hellmut.
 Abstract: The structure of binary (SiO2)100-x-(P2O5)x glasses has been investigated by Raman scattering, 29Si and 31P magic angle spinning (MAS) as well as static 31P NMR spectroscopy. 29Si chemical shift trends reflect the successive replacement of Si-O-Si by Si-O-P linkages as the compositional parameter x is increased. While 31P MAS NMR does not resolve separate phosphate species, the static 31P 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 31P 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 five- and 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 Tg at higher P2O5 contents is correlated with the appearance of the higher-coordinated silicon species. While these higher-coordinated silicon species occur within separate microdomains, 31P 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. | |
| Journal of Physical Chemistry C |
| v. 122, n. 34, p. 19807-19815 - Ano: 2018 |
| Fator de Impacto: 4,484 |
| http://dx.doi.org/10.1021/acs.jpcc.8b06055 |  @article={002903281,author = {OLIVEIRA JR., Marcos de; AITKEN, Bruce; ECKERT, Hellmut.},title={Structure of P2O5-SiO2 pure network former glasses studied by solid state NMR spectroscopy},journal={Journal of Physical Chemistry C},note={v. 122, n. 34, p. 19807-19815},year={2018}} |