Low Thermal Expansion and High Lattice Thermal Conductivity in β-Sodalite Co₄B₆O₁₃: Enhancing the Local Rigidity of Cationic Tetrahedra Cluster

Abstract

Low thermal expansion coefficient and high thermal conductivity are essential for borate optical materials used in optics, microelectronics and optoelectronics. Herein, we focus on the β-sodalite structure, exemplified by Zn4B6O13, which consists of anionic [B6O12]6− cages and cationic [Zn4O]6+ tetrahedra. Through a molecular engineering strategy, Co4B6O13 was predicted to exhibit isotropic lower thermal expansion (9.7×10−6/K at 300 K) and higher lattice thermal conductivity (125.1 W/m·K at 300 K) as calculated by Density Functional Theory. These results reveal that the enhanced Co-O bond strength and reduced compressibility of [Co4O]6+ tetrahedra are key factors driving the improved thermal properties of Co4B6O13. In contrast, the B-O chemical bond strength within the [B6O12]6− cages shows weaker changes between Zn4B6O13 and Co4B6O13. These structural modifications lead to a higher volume modulus and lower temperature-dependent elastic constants in Co4B6O13, indicating superior mechanical performance. This study provides significant insight into designing and discovering functional material with desirable thermal properties for advanced application.