Deconvolution method of $^{29}$Si MAS NMR spectra applied to homogeneous and phase separated lanthanum aluminosilicate glasses

The structural and microstructural properties of both homogeneous and phase separated lanthanum aluminosilicate (La$_2$O$_3$-Al$_2$O$_3$-SiO$_2$ i.e. LaAS system) glasses were investigated. The microstructural observations and the structural characterization by X-ray Diffraction and by Nuclear Magnetic Resonance have highlighted the role of aluminum to favor a homogeneous vitreous aluminosilicate network by a high-level of Al/Si intermixing. A qualitative and simplified structure description is proposed from $^{29}$Si nuclear magnetic resonance spectra assignment according to Q$^n$(mAl) species by controlling the deviation of chemical parameters. According to this approach, a homogeneous distribution of non-bridging oxygen in the aluminosilicate network and Al-O-Al linkages are considered for homogeneous glasses with high Al/Si atomic ratio. Phase separated samples are characterized by a low Al/Si atomic ratio inducing spinodal or nucleation/growth phase separation according to the depolymerization level. Homogeneity degree of the samples is discussed according to the intermixing level between silicon tetrahedra and aluminum polyhedra as a function of the proportion of Q$^n$ and Q$^n$(mAl) species.