Perfectly Transparent Sr₃Al₂O₆ Polycrystalline Ceramic Elaborated from Glass Crystallization

Abstract

The highly visible and infrared (up to 6 μm) transparent Sr 3 Al 2 O 6 polycrystalline ceramic was obtained by full crystallization of the corresponding glass composition. The glass synthesis and the direct congruent crystallization processes are described, and the material transparency is discussed in light of its microstructure. This new transparent ceramic exhibits a high density (i.e., complete absence of porosity) and micrometer-scale crystallites with very thin grain boundaries. These microstructural characteristics, inherent to the preparation method, minimize light scattering and demonstrate the advantages of this synthesis route compared to the high-pressure process used for the few reported transparent polycrystalline materials. This Sr 3 Al 2 O 6 ceramic shows a H = 10.5 GPa hardness, a E r = 150 GPa reduced elasticity modulus, and a 9.6 × 10 –6 K –1 thermal expansion coefficient. Such a transparent strontium aluminate ceramic opens the way to a wide range of applications, especially photonics when doped by various doping agents. As examples, the luminescence of Sr 3 Al 2 O 6:Eu 3+ and Sr 3 Al 2 O 6:Er 3+, which show strong emissions in the visible and infrared ranges, respectively, is presented. Moreover, the Sr 3 Al 2 O 6:Ce 3+ material was found to exhibit scintillation properties under X-ray excitation. Interestingly, the analogous Sr 3 Ga 2 O 6 transparent polycrystalline ceramic material could equally be prepared using the same elaboration method, although its hygroscopicity prevents the preservation of its high transparency under normal conditions. The establishment of the key factors for the transparency of this economical and innovative synthesis method should enable the prediction of new classes of technologically relevant transparent ceramics.