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 (ρ), molar volume (V _M), glass transition temperature (T _g) and thermal expansion coefficient (α). 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 V _M and T _g, while α increases. In Li–Zn metaphosphate glasses the compositional dependence of T _g reveals a minimum, while at the borophosphate series T _g 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.