Effects on the characteristics of bonding and local structure in molybdenum-lead-lead dioxide glasses and vitroceramics

Abstract

Abstract Molybdenum ions doped lead-lead dioxide glasses and vitroceramics of the xMoO 3 ·(100−x)[4PbO 2 ·Pb] system where x = 0, 5, 10, 20, 30, 40 and 50mol% MoO 3 were obtained by melt quenching method. The FTIR spectra show that the main structural units of lead atoms form chains with Mo O Mo bridge bonds in [MoO 6 ] structural units between which there are isolated [MoO 4 ] irregular tetrahedral units. The number of the [MoO 4 ] structural units increases with increasing the MoO 3 concentration of samples up to 50mol%. UV–Vis spectra show noticeable changes of the intensity of absorption bands located in the 280–400 nm region after adding of MoO 3 to the host matrix. These changes can be correlated with the contributions of Pb +2 , Mo +3 and Mo +5 ions. The EPR spectra show resonance lines situated at g∼5.2 and 2 due to the presence of Mo +3 and Mo +5 ions. The presence of both lead and molybdenum ions in the vitreous matrix generates a competition regarding their coordination with oxygen ions which leads to modifications of the gap energy values. Accordingly, these modifications cause the depolimerization of the host network, the increase of the structural disorder and formation of Pb 2 MoO 5 and PbO crystalline phases, in agreement with XRD data. Our quantum chemical calculations on the local structure of the studied vitroceramic network show that the doping of the host matrix with molybdenum ions changes the bond length and bond angles of the vibrating structural units. The accommodation of the host network with progressively higher MoO 3 contents is possible by the increase of the amount of [MoO n ] polyhedrons in the vicinity of the [PbO 3 ] structural units. It can be pointed out that the favourable environment of the host matrix offers the possibility to the molybdenum ions to choose some preferred sites of coordination.