FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron-lead-tellurate glasses

Simona Rada (1) , Adriana Dehelean (1, 2) , Eugen Culea (1)

1 Department of Physics
2 National Institute for Research and Development of Isotopic and Molecular Technologies

In this work, the effects of iron ion intercalations on lead-tellurate glasses were investigated via FTIR, Raman and UV-Vis spectroscopies. This homogeneous glass system has compositionsFeO·(100−)[4TeO·PbO], where = 0-60 mol%. The presented observations in these mechanisms show that the lead ions have a pronounced affinity towards [TeO] structural units, resulting in the deformation of the Te-O-Te linkages, and leading to the intercalation of [PbO] ( = 3, 4) and [FeO] ( = 4, 6) entities in the [TeO] chain network. The formation of negatively charged [FeO] structural units implies the attraction of Pb ions in order to compensate for this electrical charge. Upon increasing the FeO content to 60 mol%, the network can accommodate an excess of oxygen through the formation of [FeO] structural units and the conversion of [TeO] into [TeO] structural units. For even higher FeO contents, Raman spectra indicate a greater degree of depolymerization of the vitreous network than FTIR spectra do. The bands due to the Pb-O bond vibrations are very strongly polarized and the [TeO] structural units convert into [TeO] units via an intermediate coordination stage termed "[TeO]" structural units. Our UV-Vis spectroscopic data show two mechanisms: (i) the conversion of the Fe to Fe at the same time as the oxidation of Pb to Pb ions for samples with low FeO contents; (ii) when the FeO content is high ( ≥ 50 mol%), the Fe ions capture positive holes and are transferred to Fe ions through a photochemical reaction, while the Pb ions are formed by the reduction of Pb ions. DFT calculations show that the addition of FeO to lead-tellurate glasses seems to break the axial Te-O bonds, and the [TeO] structural units are gradually transformed into [TeO]- and [TeO]-type polyhedra. Analyzing these data further indicates a gradual conversion of the lead ions from covalent to ionic environment. There is then a charge transfer between the tri- and tetracoordinated tellurium atoms due to the capacity of the lead-tellurate network to form the appropriate coordination environments containing structural units of opposite charge, such as iron ions, [FeO].

Mots clés: Iron-lead-tellurate glasses; FTIR and UV-Vis spectroscopy; DFT calculations

Simona Rada, Adriana Dehelean, Eugen Culea. FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron-lead-tellurate glasses. Journal of Molecular Modeling, 2010, 17 (8), pp.2103-2111. ⟨10.1007/s00894-010-0911-5⟩. ⟨hal-00654145⟩