Structure and crystallization of (1 − x)(33.33Li2O-33.33Fe2O3-33.33P2O5) − xB2O3 glasses

The nominal composition of 33.33Li2O-33.33Fe2O3-33.33P2O5 is difficult to generate bulky glass via the normal melt-quenching route. The experiments showed that the addition of B2O3 benefited the formation of glass. Structure and crystallization behavior of (1 − x)(33.33Li2O-33.33Fe2O3-33.33P2O5) − xB2O3 (x = 5, 10, 15 and 20 mol%) glasses were investigated using Fourier transform infrared spectroscopy, differential thermal analysis and X-ray diffraction. The analysis results indicate the formation of [BO4] tetrahedra within the glass network upon adding B2O3. Mainly due to the larger volume of [BO4] compared with [PO4], the density and the chemical durability of the glass decrease with the inclusion of B2O3. On the other hand, the integration and continuity of glass network increase due to the formation of BOP bonds. As a result, the glass transition temperature increases with B2O3. However, when the content of B2O3 is more than 15 mol%, [BO3] appears leading to large decreases in the density and the chemical stability of the glass. It is evidenced that more integrated network of glass samples containing 5 and 10 mol% of B2O3 increases the possibility of phase separation in the glasses, contributing to the mixed surface and bulk crystallization mechanisms in these two samples. In contrast, the samples containing 15 and 20 mol% only show surface crystallization. All heat treated samples have main crystallization phases of Li3Fe2(PO4)3 and LiFePO4.