Structural properties of molybdenum-lead-borate glasses

Glasses and glass ceramics in the system xMoO(3)center dot(100 -x)[3B(2)O(3)center dot 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-) molybclate 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 6s(2) configuration show strong absorption in the ultraviolet due to parity allowed s(2)-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 similar to 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. (C) 2010 Elsevier B.V. All rights reserved.