Effects of Al3+, W6+, Nb5+ and Pb2+ on the structure and properties of borotellurite glasses

Abstract The effects of addition of Al3 +, W6 +, Nb5 + and Pb2 + on the density, thermal, optical properties of borotellurite glasses and on the B–O, Te–O and Al–O speciation are studied. Density maximizes in glasses containing Pb2 + and minimizes in glasses with Al3 +. The optical absorption cut-off wavelength increases with the addition of heavy metal ions while Al3 + shifts it to lower wavelengths. W6 +, Nb5 + and Al3 + strengthen the borotellurite network and enhance the glass transition temperatures, however Pb2 + decreases it. The glass transition temperature is a linear function of the average single bond energy of the glass network. 11B Magic Angle Spinning (MAS) Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared studies found that the BO4 structural units are unstable in the presence of Al3 +, W6 + and Nb5 +, however Pb2 + has an opposite effect and promotes the formation of BO4. 27Al MAS NMR showed that alumino-borotellurite glasses contain AlO6, AlO5 and AlO4 structural units whose relative concentrations depend on alumina mol%. Raman spectroscopy was used to determine Te–O coordination in glasses, the later decreased on adding metal ions and Al3 + produced a maximum suppression of TeO4 units.