Polyhedral units and network connectivity in calcium aluminosilicate glasses from high-energy X-ray diffraction

Structure factors for Cax/2AlxSi1-xO2 glasses (x = 0,0.25,0.5,0.67) extende d to a wave vector of magnitude Q = 40 Angstrom(-1) have been obtained by h igh-energy x-ray diffraction. For the first time, it is possible to resolve the contributions of Si-O, Al-O, and Ca-O coordination polyhedra to the ex perimental atomic pair distribution functions. It has been found that the c onnectivity of Si/Al-O tetrahedral network decreases with increasing x due to the emerging of nonbridging oxygens located on Si-O tetrahedra. Calcium maintains a rather uniform coordination sphere for all values of x and so i t plays a certain role in determining the glass structure.