Polyhedral Units and Network Connectivity in Calcium Aluminosilicate Glasses from High-Energy X-Ray Diffraction

摘要: Structure factors for Cax2AlxSi12xO2 glasses x 0, 0.25, 0.5, 0.67 extended to a wave vector of magnitude Q 40 A 21 have been obtained by high-energy x-ray diffraction. For the first time, it is possible resolve contributions Si-O, Al-O, and Ca-O coordination polyhedra experimental atomic pair distribution functions. It has found that connectivity SiAl-O tetrahedral network decreases with increasing due emerging nonbridging oxygens located on Si-O tetrahedra. Calcium maintains rather uniform sphere all values so plays certain role in determining glass structure. PACS numbers: 61.43.–j, 61.10.–i Silicate glasses, general, aluminosilicate particular, are great industrial geological importance. Despite this, some very basic issues about their structure still not well established. known silica continuous corner-shared tetrahedra [1]. At vertex each tetrahedron, shared between two tetrahedra, an oxygen atom as bridging oxygen. When Si 41 partially replaced another former such Al 31 and, addition, modifier cation Ca introduced balance charge, changes. The change involves gradual substitution Al-O ones so-called (NBO) linking one or polyhedral unit Ca-based [2]. presence NBO’s, i.e., breaking network, large effect thermodynamics important properties viscosity melt exact nature ion (Ca) way NBO’s into subject intensive research [3–7] yet fully resolved. Al, too, issue quite time [4]. By utilizing high fluxes rays available at third generation synchrotron sources we real-space resolution functions (PDF’s) from series 0.67. This allowed us, different bonds r 1.60 1.75 A, respectively, study independently. proved impossible lower structural studies up now because similar scattering cross sections other both neutrons. studied testosilicate compositions whereby cations exactly charge priori necessary them act breakers. In this case, was thought they occupy interstitial sites random do participate formation Recent NMR results draw simple view question finding spectroscopic evidence 10 times more than expected nominal composition Ca0.25Al0.5Si0.5O2 [7]. Our data sample quantitative agreement view. They also reveal interesting facts network. turns out predominantly but evidenced fact average remains constant approximately 4.0(1) while drops 3.2(1) when increases 0 Interestingly, environment ions defined regardless SiAl ratio abundance NBO’s. PDF, Gr 4prrr 2r ,g ives deviation local, rr, average, r0, number density describes arrangement materials. sine Fourier transform experimentally observable total factor, SQ,