An investigation of Al 2 O 3 induced variations in the structural parameters in strontium borosilicate glasses using solid state NMR.

The physical properties of oxide glasses are crucially dependent on the atomistic structural speciation. In this study, we investigate the variation in the local ordering in the glass network of strontium borosilicate glasses (34.82 SrO, 51.84 B 2 O 3 , 13.34 SiO 2 in mol%) with a progressive substitution of B 2 O 3 by Al 2 O 3 and estimate the structural parameters: the oxygen packing fraction, and the average network coordination number. The coordination of the network forming cations at various glass compositions is determined using 11 B, 27 Al, and 29 Si solid-state nuclear magnetic resonance (SSNMR). The SSNMR reveals that at the higher substitution of B 2 O 3 by Al 2 O 3 in the glass composition, the coordination network of Al 3+ exists predominantly in the 4 coordinated state, the network forming B 3+ cations transform from a tetrahedral BO 4 to a trigonal BO 3 structure, and the Q 4 form of silicates is dominant. The average coordination number and the oxygen packing fraction were calculated using the parameters obtained from the SSNMR results, and it is observed that the average coordination number decreases, and the oxygen packing fraction increases on incorporating Al. It is interesting to note that some of the thermophysical properties of these compositions closely follow the pattern shown by the average coordination number and the oxygen packing fraction.