Local structure around lead, barium and strontium in waste cathode-ray tube glasses

Cathode-ray tubes (CRTs) are made of two different kinds of glasses. The front part, panel, or screen, is made of barium- and strontium-containing glasses, while the rear part, the funnel, is made of lead-containing glasses. The structure and the role of these elements in the glasses are different: lead oxide is generally considered as a network intermediate whereas barium and strontium oxides as network modifiers. To study the local structure around the three aforementioned heavy elements we have used X-ray absorption spectroscopy (XAFS) on Pb and Ba LIII-edges and Sr K-edge as well as X-ray photoemission spectroscopy (XPS) analyzing the Pb 4f, Sr 3p, Ba 3d, Si 2p and O 1s core peaks. Due to the complex formulation of these glasses the coordination of lead and strontium could be affected compared with the local structure of binary glassy systems. We demonstrate that the average coordination number of lead is close to three (Pb–O distances being 2.24 A) as in other lead silicate glasses. In case of strontium, the coordination number is found close to five (Sr–O distances being 2.52 A) similar to that in Sr-containing glasses.