Structural Study on PbO–SiO2 Glasses by X-Ray and Neutron Diffraction and29Si MAS NMR Measurements.

Structure ofxPbO–(100− x)SiO2 (x=25–89) glasses has been investigated by means of the X-ray and neutron diffraction and29Si MAS NMR measurements. In the radial distribution functions of all the glasses, the Pb–O correlation was observed at 0.23 nm, indicating that the PbO3 trigonal pyramids units do exist in the whole glass forming composition range. Furthermore the existence of the first Pb–Pb correlation at∼0.385 nm in the whole composition range suggests that the basic structural unit is considered to be a Pb2O4 unit, which consists of the edge-shared PbO3 trigonal pyramids. These results strongly imply that the Pb2O4 units participate in the glass network constructed by SiO4 tetrahedra even at low PbO content. Differing from other lead-containing glass systems, these structural characteristics of Pb ions in the PbO–SiO2 glass system are responsible for the extremely wide glass-forming region. [ABSTRACT FROM AUTHOR]