Recently, application of in situ, high temperature nuclear magnetic re
sonance (NMR) spectroscopy to study silicate, berate and aluminate mel
ts has lead to a variety of findings on structural changes with temper
ature (particularly in cation coordination number), and on the dynamic
s of exchange and diffusion. New data are presented on chemical shifts
and spin-lattice relaxation of Na-23 in a number of silicate liquids
to about 1200 degrees C, and these results are discussed in light of o
ther recent studies. These results clearly demonstrate the mixed alkal
i effect on cation motion. New high temperature magic angle spinning B
-11 NMR spectra for a sodium berate liquid are also presented. As in p
revious studies of aluminate and silicate melts, the latter data set s
uggests that the mechanism of viscous flow is closely tied to local ex
change of cationic species.