23Na chemical shifts and local structure in crystalline, glassy, and molten sodium borates and germanates

A simple correlation between average Na-O bond length and Na-23 isotropic chemical shift in crystalline germanates and berates has been established, similar to existing correlations for sodium in silicates and carbonates. This empirical trend is discussed in terms of a decreasing paramagnetic contribution to the chemical shift with increasing average bond length. The correlation is then applied to data for sodium berate and germanate glasses and melts from room temperature to 1200 degrees C, where both structural and compositional effects on the chemical shift are apparent. (C) 1997 Elsevier Science B.V.