Local cation environments in mixed alkali silicate glasses studied by multinuclear single and double resonance magic-angle spinning NMR

Abstract The local cation environments in single and mixed alkali silicate glasses are discussed on the basis of chemical shift trends observed in field-dependent multinuclear ( 29 Si, 23 Na, 6,7 Li) magic angle spinning, as well as 29 Si{ 23 Na} and 29 Si{ 7 Li} rotational echo double resonance (REDOR) NMR results. Within the series (Li 2 O) x (SiO 2 ) 1- x and (Na 2 O) x (SiO 2 ) 1- x the alkali cation chemical shifts depend systematically on the network modifier concentration, reflecting changes in the alkali ion environments as the content of non-bridging oxygen species increases in the silicate network. Within the series [{Li 2 O} 1- y {Na 2 O} y ] 0.4 {SiO 2 } 0.6 systematic trends in the 7 Li and 23 Na chemical shifts indicate continuous changes in the cation environment as a function of Na/(Na + Li) ratio, consistent with intimate mixing of the cations. This interpretation is corroborated by results from 29 Si{ 23 Na} and 29 Si{ 7 Li} rotational echo double resonance (REDOR) NMR difference spectroscopy.