Study of lithium–zinc borophosphate glasses

Mixed lithium–zinc borophosphate glasses were prepared and studied in three compositional series xLi2O–(50)x)ZnO–50P2O5, xLi2O–(50)x)ZnO–10B2O3– 40P2O5 and xLi2O–(50)x)ZnO–20B2O3–30P2O5 with x = 0, 10, 20, 30, 40 and 50 mol% Li2O. The obtained glasses were characterized by the measurements of the density (q), molar volume (VM), glass transition temperature (Tg) and thermal expansion coefficient (a). For the investigation of structural changes 11B and 31P MAS NMR and Raman spectroscopy were applied. The replacement of zinc by lithium in borophosphate glasses slightly decreases VM and Tg, while a increases. In Li–Zn metaphosphate glasses the compositional dependence of Tg reveals a minimum, while at the borophosphate series Tg decreases monotonously with increasing Li2O content. Chemical stability of Li–Zn borophosphate glasses is very good for glasses with x = 0–30 mol% Li2O. Spectral studies showed in the glass series with 10 mol% B2O3 only the presence of BO4 sites. In the glasses with 20 mol% B2O3 the presence of BO3 and two BO4 sites was revealed in ZnO-rich glasses and only one BO4 site in Li2O-rich glasses; the number of BO3 groups decreases with increasing Li2O content which is ascribed to the formation of P–O–Zn covalent bonds in ZnO-rich glasses.