title: FTIR, Raman, and UV-Vis spectroscopic and DFT investigations of the structure of iron-lead-tellurate glasses.
abstract: 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 compositions xFe(2)O(3)·(100-x)[4TeO(2)·PbO(2)], where x = 0-60 mol%. The presented observations in these mechanisms show that the lead ions have a pronounced affinity towards [TeO(3)] structural units, resulting in the deformation of the Te-O-Te linkages, and leading to the intercalation of [PbO( n )] (n = 3, 4) and [FeO( n )] (n = 4, 6) entities in the [TeO(4)] chain network. The formation of negatively charged [FeO(4)](1-) structural units implies the attraction of Pb(2+) ions in order to compensate for this electrical charge. Upon increasing the Fe(2)O(3) content to 60 mol%, the network can accommodate an excess of oxygen through the formation of [FeO(6)] structural units and the conversion of [TeO(4)] into [TeO(3)] structural units. For even higher Fe(2)O(3) 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(4)] structural units convert into [TeO(3)] units via an intermediate coordination stage termed "[TeO(3+1)]" structural units. Our UV-Vis spectroscopic data show two mechanisms: (i) the conversion of the Fe(3+) to Fe(2+) at the same time as the oxidation of Pb(2+) to Pb(+4) ions for samples with low Fe(2)O(3) contents; (ii) when the Fe(2)O(3) content is high (x ≥ 50 mol%), the Fe(2+) ions capture positive holes and are transferred to Fe(3+) ions through a photochemical reaction, while the Pb(2+) ions are formed by the reduction of Pb(4+) ions. DFT calculations show that the addition of Fe(2)O(3) to lead-tellurate glasses seems to break the axial Te-O bonds, and the [TeO(4)] structural units are gradually transformed into [TeO(3+1)]- and [TeO(3)]-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(4)](1-).
authors.affiliation: Department of Physics, Technical University of Cluj-Napoca, 400641 Cluj-Napoca, Romania. Simona.Rada@phys.utcluj.ro
authors.forename: Simona
authors.initials: S
authors.lastname: Rada
authors.forename: Adriana
authors.initials: A
authors.lastname: Dehelean
authors.forename: Eugen
authors.initials: E
authors.lastname: Culea
mesh_terms: D003198:Computer Simulation; D005898:Glass / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007854:Lead / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D013059:Spectrum Analysis, Raman; D013691:Tellurium / Q000737:chemistry*
chemical_list: D007854:Lead; D007501:Iron; D013691:Tellurium