Thermal properties and crystallization of BaO–MoO3–P2O5 glasses

Abstract

The thermal behavior and crystallization of barium molybdate-phosphate glasses were studied in two compositional series, namely A: (100 − x)Ba(PO3)2–xMoO3 (with x = 0–70 mol%) and B: 50BaO–yMoO3–(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 31P MAS NMR spectroscopy. Large thermal stability of glass with a composition 35BaO–30MoO3–35P2O5 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.