Mechanical properties of phosphate glasses

The strengths of fibers drawn from three metaphosphate glasses [NaPO3, Zn(PO3)2 and a Schott laser glass, LG 770, with the approximate molar composition 20K2O–10MgO–10Al2O3–60P2O5] and a pyrophosphate (P2O7) glass of nominal composition 40FeO3–60P2O5 have been measured in 2-point bending at room temperature and at 77 K. While the three metaphosphate glasses have relatively smaller strengths at low temperature (∼3 GPa), the iron phosphate glass has a strength at this temperature (∼6 GPa), 1/2 that of silica (13 ± 2 GPa). No correlation was found with either the square root of Young’s modulus (E)1/2 or fracture toughness (KIC), but an understanding of the results was obtained by considering the overall integrity of the individual glass networks.