Solid state 1H NMR study, humidity sensitivity and protonic conduction of gel derived phosphosilicate glasses

Abstract

¹H Magic Angle Spinning (MAS) NMR and ¹H T₁ and T_1ρ relaxation times measurements were used to investigate structural aspects of gel derived glasses of composition 10P₂O₅·90SiO₂ (10P) and 30P₂O₅·70SiO₂ (30P), with the aim of understanding the different humidity sensitive behaviour observed for films of the same composition. The experimental evidence suggests that 10P and 30P gel samples heat treated at 100 °C have a similar POH environment while further heating causes a different structural evolution of POH units. In particular, the 30P sample heat treated at 400 °C shows a single ¹H resonance while a number of resonances are seen in the ¹H spectrum of the 10P sample heat treated at 400 °C. Further evidence of the different structure of 10P and 30P samples was given by the NMR relaxation times measurements, the gels were found to be heterogeneous on a nanometric scale. Domains, about 60 nm in size, related to ¹H resonance in POH were evenly distributed in the matrix of both gels, only in the 10P gel also larger domains (about 700 nm) were found that can be related to ¹H resonance in SiOH groups. Finally, MAS in combination with variable temperature static NMR spectra provided detailed information on the network structural features present in the 30P sample heat treated at 300 °C as well as in the 10P sample heat treated at 400 °C and allowed investigation of the dynamic processes taking place in these samples.