Synthesis and characterization of niobium phosphate glasses containing barium and potassium

The structural characteristics of phosphate glasses containing different amounts of Nb were investigated by X-ray diffraction, thermal analysis, Raman, and infrared spectroscopy. Phosphate glasses can be produced with relatively high amount of niobium by increasing the cooling rate without crystallization. Niobium is a glass former, is located in octahedral sites, and replaces tetrahedral phosphate groups by P, Nb, and O linked mixed chains. The density increases from 3.32 g/cm3 to 3.73 g/cm3, the elastic modulus increases from 56 GPa to 78 GPa, and the linear thermal expansion coefficient decreases from 24.7 × 10−6 °C−1 to 7.9 × 10−6 °C−1 as the amount of Nb increases. The glass transition temperature (Tg) increases from 480 °C to 653 °C as the amount of Nb increases from 5 to 37 mol % because the Nb–O–P and Nb–O–Nb linkages are stronger than the O–P bond, requiring higher temperatures for relaxation. Electrical measurements showed that the activation energy for ionic conduction increases from 0.46 eV to 0.59 eV for glasses containing 19–32 mol % of Nb2O5.