The surface hydroxyl groups of γ-alumina dehydroxylated at 500 °C were studied by a combination of one- and two-dimensional homo- and heteronuclear (1)H and (27)Al NMR spectroscopy at high magnetic field. In particular, by harnessing (1)H-(27) Al dipolar interactions, a high selectivity was achieved in unveiling the topology of the alumina surface. The terminal versus bridging character of the hydroxyl groups observed in the (1)H magic-angle spinning (MAS) NMR spectrum was demonstrated thanks to (1)H-(27) Al RESPDOR (resonance-echo saturation-pulse double-resonance). In a further step the hydroxyl groups were assigned to their aluminium neighbours thanks to a {(1)H}-(27) Al dipolar heteronuclear multiple quantum correlation (D-HMQC), which was used to establish a first coordination map. Then, in combination with (1)H-(1) H double quantum (DQ) MAS, these elements helped to reveal intimate structural features of the surface hydroxyls. Finally, the nature of a peculiar reactive hydroxyl group was demonstrated following this methodology in the case of CO2 reactivity with alumina.

In this paper, the concept of mixed glass former effect (MGFE), an intriguing phenomenon leading to glasses with high conductivity and increased thermal properties, has been revisited thanks to the combination of (i) an efficient elaboration technique that helped in producing for the first time a series of Li-rich borophosphate glasses from pure phosphate to pure borate and (ii) a structural investigation based on advanced 1D/2D solid state NMR performed at standard and very high magnetic fields (9.4 and 18.8 T) using very recently developed methods ( 11 B{ 31 P} D-HMQC, 11 B DQ-SQ). Homogeneous glasses, completely free of crystallization and exhibiting unreported and high values of conductivity when compared to other oxide-based materials, were prepared all along the 45Li 2 O-55[xB 2 O 3 -(1Àx) P 2 O 5 ] line, thanks to an ultra-fast quenching method. It allowed investigation of the relation between electrical/thermal properties and structure over the full range of composition. The advanced 1D/2D solid state NMR investigation helped in producing unreported and deep insights into the glass structure about (i) the multiple BO 4 chemical environments, (ii) the BO 3 -BO 4 connectivity, (iii) the wide range of phosphate speciation (described with the Q n m,BOx notation) and (iv) unexpected and unreported correlations between trigonal boron and phosphate species suggesting an original structure where both tetragonal and trigonal boron interact with the phosphate species. While confirming that the MGFE has a direct impact on the vitreous transition temperature, this investigation helped in giving the first clear evidence of the link that exists between structure and conductivity changes in these solid electrolytes.