Thermal properties and crystallization of BaO-MoO3-P2O5 glasses

The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A: (100 - x)Ba(PO3)(2)-xMoO(3) (with x = 0-70 mol%) and B: 50BaO-yMoO(3)-(50 - y)P2O5 (with y = 0-15 mol% MoO3). Thermal properties were studied with differential thermal analysis and dilatometry. Glass transition temperature increases in series A in the range of 0-40 mol% MoO3 and then decreases with a further increase in MoO3 content, whereas the thermal expansion coefficient in series A reveals a minimum at 50 mol% MoO3. These trends are not observed in series B, where the glass transition temperature increases in the range of 0-15 mol% MoO3 and the thermal expansion coefficient almost does not change. Crystallization of these glasses was studied by X-ray diffraction analysis, Raman and P-31 MAS NMR spectroscopy. Large thermal stability of glass with a composition 35BaO-30MoO(3)-35P(2)O(5) toward crystallization was demonstrated. Crystallization of glasses resulted in the formation of the compound Ba(MoO2)(2)(PO4)(2) in this ternary system. Raman spectroscopy also provided information on the formation of glass-crystalline samples in some studied compositions.