Glass formation in the MoO3–CuO–PbO system

Glasses in the MoO3–CuO–PbO system are obtained at high cooling rates (104–105 K/s) and characterized using X-ray diffraction (XRD), differential thermal analysis (DTA), infrared (IR) and X-ray photoelectron spectroscopy (XPS). Two glass formation regions are determined: one with compositions having a high MoO3 content (50–80 mol%) and the other in the PbO-rich compositions (65–80 mol%). In the region of MoO3-rich compositions the building units of the amorphous network are МоО6, МоО4 and CuO4 groups. For these high MoO3 contents and respectively low PbO concentrations, the lead oxide is supposed to act as a network modifier while at high content PbO is found to be the main glass network former. In latter case the structure of glasses is formed by chains of PbOn (n = 3, 4) polyhedra, between which there are isolated MoO4 and CuO4 complexes. IR and XPS data reveal the existence of Mo–O–Mo, Mo–O–Me(Me’) (where Me = Cu2+, Cu1+ and Me’ = Pb) and Me(Me’)–O–Me(Me’) bonds in the amorphous network. Surprising result is found for low PbO content (10 mol%) where the lead oxide acts as glass network modifier: the actual MoO3 content drops strongly which is accompanied with a significant increase of the actual CuO content with respect to their nominal MoO3–CuO composition. Such effect is not observed in PbO-rich composition (70 mol%) where PbO has a role of network former.