Transparent Dense Polycrystalline Ceramics for Photonics Applications Synthesized by Direct Crystallization from a Glassy Precursor
Transparent polycrystalline ceramics are an emerging class of photonic quality materials competing with single crystal technology for a diverse range of applications including high-energy lasers, scintillating devices, optical lenses, and transparent armor. Polycrystalline ceramics offer several advantages, particularly in the fabrication of complex shapes and large-scale industrial production, and enable greater and more homogenous doping of optically active ions than is possible in single crystals. A limited number of either cubic or nanocrystalline transparent polycrystalline ceramics are known, but require complex and time-consuming synthetic approaches.
Our recent work demonstrates the possibility to obtain for the first time fully dense transparent polycrystalline ceramics by simple direct and complete crystallization from glass. This is demonstrated for the previously unreported composition, BaAl4O7, which exhibits two orthorhombic polymorphs with micrometer grain size, both optically transparent in the visible range.
The crystallographic structures of these materials have been determined ab initio from powder diffraction. From these structural models, the refractive index components (nx, ny and nz) have been calculated, giving access to the birefringence. The transparency of these materials will be discussed from these results and the microstructures observed. Lastly, the same innovative synthetic route has been applied to new strontium aluminosilicate compositions, evidencing new and cost-effective solid solutions elaborated as highly transparent polycrystalline ceramics.