Structure and physicochemical properties of CaO-P2O5-Nb2O5-Na2O glasses

Calcium phosphate glasses were prepared by adding Nb2O5 and Na2O. Spectroscopic analyses showed that the glasses included niobate groups, such as NbO4 and NbO6. The amount of NbO4 units, which was considered to be a network former, increased with the increase in Nb2O5 content, and the formation of an Nb-O-P bond appeared. The ion-releasing ability of the glasses in the Tris-buffer solution depended on their chemical composition. The process window of the glass, which was estimated from the temperature range between the glass transition and the onset of crystallization, increased with the increase of the Nb2O5 content of the glass. The excellent chemical durability and glass-forming ability of calcium phosphate glass were considered to originate from the formation of the Nb-O-P bond.