Tailoring the Thermal Expansion of Glass‐Ceramics by Controlled Twofold Crystallization of Li 2 Si 2 O 5 and CsAlSi 5 O 12

The mechanical and optical properties of Li 2 Si 2 O 5 glass‐ceramics can be precisely controlled via the crystal morphology and content. However, the materials' coefficient of thermal expansion (CTE) depends on the fraction as well as the CTE of Li 2 Si 2 O 5 and the residual glass phase, and therefore covers a rather narrow range between 10.2 and 11.3 *10 −6 K −1 (100–400°C). This study presents a way to tailor the CTE of lithium disilicate‐based glass‐ceramics by controlled twofold precipitation of Li 2 Si 2 O 5 and CsAlSi 5 O 12 as a minor crystal phase with high CTE from homogenous Cs 2 O comprising bulk base glasses. The Cs 2 O content in the base glass significantly influences the nucleation and crystallization process of Li 2 Si 2 O 5 as well as the microstructure of the glass‐ceramic materials. While the precipitation of Li 2 SiO 3 and Li 2 Si 2 O 5 starts at temperatures ≤700°C, CsAlSi 5 O 12 forms in parallel to the enhanced formation of Li 2 Si 2 O 5 as a result of Li 2 SiO 3 dissolution at crystallization temperatures >850°C. Glass‐ceramics with a CTE ranging from 11 to 13.1*10 −6 K −1 (25–500°C) and a mean biaxial strength ≥370 MPa were produced. The preliminary study of this glass system proofs the potential of twofold crystallization to control the CTE of lithium disilicate glass‐ceramics.