Structure and properties of potassium niobato-borophosphate glasses

Abstract Bulk glasses of the series (1 − x )[0.5K 2 O–0.1B 2 O 3 –0.4P 2 O 5 ]– x Nb 2 O 5 with x = 0–45.7 mol% Nb 2 O 5 were prepared by slow cooling in air and investigated by Raman, 31 P, and 11 B MAS NMR spectroscopy. The incorporation of Nb 2 O 5 into the parent borophosphate glass results in a substantial increase in the glass transition temperature and chemical durability of glasses. Raman spectra showed that Nb atoms form distorted NbO 6 octahedra, which are isolated at low Nb 2 O 5 content, whereas at higher Nb 2 O 5 content they form clusters. 11 B NMR spectra of the glasses revealed the interaction between Nb 2 O 5 and BO 4 tetrahedral units, which results in a partial transformation of tetrahedral BO 4 units to trigonal BO 3 units and the formation of mixed B(OP) 4− n (ONb) n units.