title: Structural properties of molybdenum-lead-borate glasses.
abstract: Glasses and glass ceramics in the system xMoO₃·(100 - x)[3B₂O₃·PbO] with 0 ≤ x ≤ 30 mol% have been prepared from melt quenching method and characterized by means of X-ray diffraction, FTIR, UV-VIS and EPR spectroscopy. We have examined and analyzed the effects of systematic molybdenum ions intercalation on lead-borate glasses and glass ceramics with interesting results. The observations present in these mechanisms show the lead ions bonded ionic have a strong affinity towards [BO₃] units containing non-bridging oxygens and [MoO₄]²⁻ molybdate units. The pronounced affinity towards molybdate anions yields the formation of the PbMoO₄ crystalline phase. Then, the excess of oxygen can be supported into the glass network by the formation of [MoO₆] and [Mo₂O₇] structural units. Pb²(+) ions with 6s² configuration show strong absorption in the ultraviolet due to parity allowed s²-sp transition and yield an absorption band centered at about 310 nm. The changes in the features of the absorption bands centered at about 310 nm can be explained as a consequence of the appearance of additional absorption shoulder due to photoinduced color centers in the glass such as the formation of borate-molybdate and lead-molybdate paramagnetic defect centers in the glasses. The concentration of molybdenum ions influences the shape and width of the EPR signals located at g ∼ 1.86, 1.91 and 5.19. The microenvironment of molybdenum ions in glasses is expected to have mainly sixfold coordination. However, there is a possibility of reduction of a part of molybdenum ions from the Mo⁶(+) to the Mo⁵(+) and Mo⁴(+) to the Mo³(+) states.
authors.affiliation: Technical University of Cluj-Napoca, B-dul Muncii, nr. 103-105, 400641 Cluj-Napoca, Romania.
authors.forename: M
authors.initials: M
authors.lastname: Rada
authors.forename: S
authors.initials: S
authors.lastname: Rada
authors.forename: P
authors.initials: P
authors.lastname: Pascuta
authors.forename: E
authors.initials: E
authors.lastname: Culea
mesh_terms: D001881:Borates / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D005898:Glass / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D007854:Lead / Q000737:chemistry*; D015394:Molecular Structure; D008982:Molybdenum / Q000737:chemistry*; D010084:Oxidation-Reduction; D055672:Static Electricity
chemical_list: D001881:Borates; D007477:Ions; D007854:Lead; D008982:Molybdenum