Local structure of Si-Al-Ca-Na-O glasses from coupled neutron and X-ray total scattering data.

Amorphous materials became significantly important and more widely studied during the last few decades, due the their increasingly widespread applications in materials science and technology. Their local structure seems to have a very strong bond with those properties: in this paper, the local structure of Si-Al-Ca-Na-O glasses is studied by means of total scattering. EPSR simulations, coupling neutron, and X-ray data have been used to study glass samples (as a function of composition), with a composition close to the one used in their technological applications (ceramic glazes), providing a consistent structural model. The disordered structure of these materials has been evaluated in terms of network-forming/modifier elements. The network-forming elements (silicon and aluminum) show coordination numbers and bond angles that are consistent with a tetrahedral arrangement. In contrast, network-modifying elements (Ca and Na, whose content is different in all samples) depolymerize the network, increasing the number of nonbridging oxygens. This structural information is required to rationalize many important technological properties of these materials, such as the glass transition temperatures and thermal expansion, that control their efficiency as glazes.