Low thermal expansion and high lattice thermal conductivity in β-sodalite Co4B6O13: enhancing the local rigidity of the cationic tetrahedral 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 a lower isotropic thermal expansion (9.7 × 10⁻⁶ K⁻¹ at 300 K) and a higher lattice thermal conductivity (125.1 W m⁻¹ K⁻¹ 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 smaller changes between Zn₄B₆O₁₃ and Co₄B₆O₁₃. These structural modifications lead to a higher volume modulus and lower temperature-dependent elastic constants in Co₄B₆O₁₃, resulting in superior mechanical performance. This study provides significant insight into designing and discovering functional materials with desirable thermal properties for advanced applications.