Structure of Ta2O5 containing Phosphate Invert Glasses Prepared by Liquid Phase Method

Tantalum-containing phosphate invert glasses were prepared using a liquid phase method under ambient conditions. In our previous study, the ion-releasing behavior ( i.e. chemical durability) of phosphate glasses was controlled by the amount of intermediate oxides. In this work, Ta 2 O 5 (intermediate oxide) was used to improve the chemical durability of the glasses. Ta-containing phosphate invert glasses were prepared and their structures were characterized. X-ray diffraction (XRD) patterns of the glasses exhibited broad halos, indicating an amorphous state. The amount of P 2 O 5 in the glasses increased with increasing Ta 2 O 5 content, while the amount of CaO decreased. The glasses prepared with a nominal P : Ta molar ratio of 2 : 1 showed a value of 1.87 : 1. Thus, almost all the Ta used in the synthesis was contained in the resulting glass. Raman spectra showed bands corresponding to short phosphate units such as ortho-and pyrophosphate, and the P-O-P peak was blue-shifted with increasing Ta 2 O 5 content. The P-O-Ta bonds were formed with TaO 4 tetrahedra, as new peaks at 970 cm -1 (P-O-Ta bonds) and 825 cm -1 (observed in YTaO 4 ) were observed. The glasses containing higher amounts of Ta 2 O 5 exhibited TaO 6 -rich phases, as shown by the Raman band at 630 cm -1 (Ta-O-Ta bonds) and broad XRD peaks at 2 θ = 5 ~ 10°. Therefore, Ta in the phosphate invert glasses prepared by the liquid-phase method crosslinks phosphate units in the form of TaO 4 tetrahedra, and the excess Ta exists in the form of TaO 6 octahedra as a network modifier and/or Ta 2 O 5 -rich phase.