Formation of Li₃B₇O₁₂ and O₂BF₄ phases from glass system of 0.5LiF-0.5B₂O₃ containing P₂O₅ and their structural properties

Borate glass containing lithium fluoride doped with different ratios of phosphate units was produced by conventional melting–annealing technique. Moreover, the produced samples were subjected to two steps of controlled heat treatment in order to achieve the glass–ceramic derivatives (nucleation and crystal growth regimes). Thermal expansion technique revealed that the nucleation temperature for the studied glasses is around 340 °C and the softening temperature (crystal growth) is around 432 °C to form glass–ceramic samples. Li₃B₇O₁₂ phase was observed as primary phase for the glass–ceramic samples. Also, other crystalline phases such as LiPO₃ and O₂BF₄ were formed. Structural changes of both of the glass and the glass–ceramics were investigated through the Fourier transform infrared technique (FTIR). The active range in the FTIR which distinguishes the glass and the crystalized sample is lying from 400 to 1250 cm⁻¹. The presence of LiF in B₂O₃ network changes the characteristic units of BO₃ and BO₄ units into BO₂F and BO₃F units, respectively.