6-COORDINATED SILICON IN SRO-P2O5-SIO2 GLASSES

Formation of the sis-coordinated silicon was investigated using magic angle spinning P-31 and Si-29-nuclear magnetic resonance (NMR) spectra in samples of the SrO-P2O5-SiO2 system. The six-coordinated Si, which shows the Si-29 NMR peak at -215 ppm, are formed in samples containin g more than about 45% P2O5, and less than 33% SrO. The six-coordinated Si content increases in proportion to the ratio of (P2O5 + SrO) to Si O2. The density of samples is higher than calculated assuming the four -coordinated Si. The proportion of the six-coordinated Si increases in samples prepared with slower cooling rates from lower melting tempera tures.