Zn₃GaB₆O₁₂As and Zn₄P₆N₁₂S: Isotropic Zero Thermal Expansion Materials Based on the “Cage-Restricting” Model

With the capability to keep the size invariant along all dimensions over a certain temperature range, isotropic zero thermal expansion (ZTE) materials have been attracting wide interest in many scientific and engineering fields. Herein, based on the “cage-restricting” model for the ZTE materials with β-sodalite-like structures, we design and synthesize two new isotropic ZTE materials, Zn3GaB6O12As (ZGBA) and Zn4P6N12S (ZPNS), from the molecular engineering strategies of enhancing the cage-restricting force and of increasing the rigidity of β-sodalite cages, respectively. ZGBA and ZPNS exhibit isotropic ZTE behaviors in the temperature range from 20 to 300 K, with the coefficients of thermal expansion 1.18(17)/MK and 1.37(17)/MK, respectively, both of which are lowered by ∼30–20% in comparison with their template compound Zn4B6O12S (ZBS). The mechanisms of improved isotropic ZTE in ZGBA and ZPNS are unraveled by lattice dynamic analysis and temperature-dependent crystal structure evolution. This study paves new avenues to enhance the ZTE behavior in the materials with cage-like structures and has great implication on the exploration of isotropic ZTE materials.