Investigating the Trade‐off between Optical and Mechanical Properties during Constrained Sintering of Mesomorphic Ceramic Films

Abstract Robust, transparent, and birefringent inorganic films are demanded for polarization control of high‐power lasers. While single crystals or films obtained via glancing angle deposition exhibit desirable optical properties and laser damage resistance, these methods are limited by cost and scalability. Mesomorphic ceramics as inorganic solids with liquid crystalline superstructure offer appealing transparency and birefringence but lack mechanical robustness due to their high porosity. Here, the effect of sintering on optical and mechanical properties of mesomorphic ceramics is evaluated. Films prepared by blade coating are sintered under varying conditions. Constrained sintering accomplished crystallite growth, densification, and morphological changes including necking as well as cracking while preserving the crystallographic orientation. The extent of sintering as a function of thermal treatment is quantified by morphology, surface area loss, and crystallite growth. Moreover, activation energies for surface diffusion and grain growth are estimated by surface area analysis and X‐ray diffraction peak narrowing, respectively. After sintering, birefringence decreases while Young's modulus and hardness improve as the film densifies. Upon partial sintering, mesomorphic ceramics retain transparency, high birefringence, and enhanced modulus. Laser‐induced damage threshold is measured as well. The reported results represent an important step toward the assembly and sintering of robust waveplates with high laser damage resistance.