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 networkandenhancetheglasstransition temperatures,however Pb2+decreases it.Theglasstransition temperature isa linearfunction oftheaveragesinglebondenergyoftheglassnetwork.11BMagicAngleSpinning(MAS) Nuclear Magnetic Resonance (NMR) and Fourier Transform Infrared studies found that the BO4 structural units are unstable in thepresenceof Al3+ , W6+andNb5+,howeverPb2+hasanoppositeeffectandpromotestheformation of BO4. 27Al MAS NMR showedthat alumino-borotellurite glasses contain AlO6,AlO5 and AlO4 structural units whoserelative concentrations depend onalumina mol%. RamanspectroscopywasusedtodetermineTe–O coordination in glasses, the later decreased on adding metal ions and Al3+produced a maximum suppression of TeO4 units.