Structural investigation of Li2O–B2O3–MoO3glasses and high-temperature solutions: toward understanding the mechanism of flux-induced growth of lithium triborate crystal

Abstract

MoO3 is an important flux for lithium triborate (LiB3O5) crystal growth from high-temperature solutions. Although it has been widely used, the mechanism of the MoO3 flux-induced growth of LiB3O5 crystals is still not very clear. In this paper, we present a spectroscopic investigation of the Li2O–B2O3–MoO3 ternary glasses/solutions, which were prepared from high-temperature MoO3-based solutions for LiB3O5 crystal growth. By combining all the experimental data of Raman and MAS NMR, the types of structural species and the interactions between flux and solute are discussed to understand the MoO3 flux-reduced mechanism of LiB3O5 crystallization from the high-temperature solution. Considering the activities of lithium cations, an isomerization reaction is proposed to describe the structural evolution of the BO4 tetrahedron into the BO3 triangle in boroxol due to the MoO3 flux. The transition between the boron oxide species is essential for the LiB3O5 crystal growth. On cooling, the formed boroxol rings are polymerized by the re-formation of BO4 tetrahedrons again, and gather together to form the LiB3O5 crystal phase. Finally, the MoO3 flux-induced LiB3O5 crystallization may be elucidated with the decrease of the concentration of the BO4 tetrahedron in high-temperature solutions.