High-temperature Raman spectroscopy of microstructure around the growing β-BaB₂O₄ crystal in the BaO–B₂O₃–Na₂O system

High-temperature Raman spectroscopy has been applied to study in situ the microstructure of the solution near the β-BaB₂O₄ crystal–solution interface in the BaO–B₂O₃–Na₂O growth system. A boundary layer near the crystal–solution interface was observed. In accordance with the high-temperature Raman spectroscopy and first principles calculations, a boron–oxygen structural model is proposed to explain the microstructure of the solution and growth habit. The results show that the growth solution contains a special group, [BO₂ØBOØB=O]³⁻ (Ø = bridging oxygen), which transformed to the growth unit [B₃O₆]³⁻ near the interface.