Structural studies of AgPO3-MoO3 glasses using solid state NMR and vibrational spectroscopies

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Vitreous samples (1-x) AgPO3-x MoO3 (0 <= x <= 0.5) were prepared by conventional melt-quenching and characterized by Differential Scanning Calorimetry (DSC). The structural evolution of the vitreous network was monitored by P-31 solid state nuclear magnetic resonance and Raman scattering, and assignments were aided by corresponding studies on the model compound AgMoO2PO4. The P-31 MAS-NMR data differentiate between species having two, one, and zero P-O-P linkages (Q(2) Q(1), and Q(0) species), respectively. Interatomic connectivities involving these units are revealed by two-dimensional INADEQUATE data, utilizing the formation of double quantum coherences mediated by indirect P-31-P-31 spin-spin interactions via P-O-P linkages. As this method discriminates against isolated P atoms, it also serves as an important spectral editing tool for constraining lineshape fits. Mo-95 NMR data and Raman spectra suggest that the Mo species are most likely six-coordinate, forming four P-O-Mo linkages and are otherwise invariant with composition, except at MoO3 contents >= 40 mole %, where some Mo-O-Mo bonding and/or clustering is observed. (C) 2012 Elsevier B.V. All rights reserved.