TeO₂-based (tellurite) glasses (oxidation number of Te: +IV) are excellent candidates for applications in the mid-infrared up to 5-6 µm. Besides, this family of glasses has interesting optical properties, such as high nonlinear refractive indices compared to silica glass, which is highly suitable for nonlinear applications .

Our study focuses on the TeO₂-B₂O₃-BaO system. In this ternary diagram, crystallization of certain non-centrosymmetric phases may be envisaged like BaTeO₃ or β-BaB₂O₄ which have excellent optical properties including a large effective nonlinear optical refractive index. Many different chemical compositions within this ternary diagram were thus synthesized and characterized (thermally and structurally) to first establish the glassy domain. After that, it was possible to identify specific compositions with interesting properties.

As the final goal of our work will be to achieve new barium borotellurite glass-ceramics, the aforementioned compositions were therefore selected as the initial parent glass. Indeed, glass-ceramic technology is based on the controlled crystallization of glass. And the retention of transparency during glass crystallization typically requires a homogeneous distribution of nanoscale crystals to minimize light scattering.

Finally, the choice of borotellurites is also dictated by their known tendency to display liquid phase separation. Hence, the strategy employed is to use this liquid phase separation process in order to synthesize new demixed barium borotellurite glasses. During the further partial and controlled crystallization, we then believe that the crystal growth will remain limited due to the size of the initial phase separation, resulting in a glass-ceramic nanostructure similar to the one observed in the parent glass; the control of the nano-structuration being effectively the key point to maintain the transparency of the final glass-ceramic materials.