Zero Thermal Expansion and Local Structure in K _x Mn _x Fe _{2‐ x} Mo ₃ O ₁₂ ‐Based Materials

ABSTRACT Zero thermal expansion (ZTE) material is a very interesting research topic for applications. However, achieving ZTE of single‐phase materials over a wide range remains a challenge. In this study, K _x Mn _x Fe _{2‐ x} Mo ₃ O ₁₂ were designed by adjusting the doping ratio of (KMn) ³⁺ . Local structure can be controlled to regulate thermal expansion. ZTE over a wide temperature range was achieved in the KMnFeMo ₃ O ₁₂ sample ( α _l = 0.51 × 10 ⁻⁶ K ⁻¹ , 100–800 K). A joint study of synchrotron X‐ray diffraction, neutron pair distribution function, density functional theory calculations, and Raman spectroscopy has been conducted to investigate the thermal expansion mechanism. Even though the macroscopic crystallographic structure of K _x Mn _x Fe _{2‐ x} Mo ₃ O ₁₂ ( x = 0.4–1.0) adheres to the hexagonal system ( R‐ 3 c ) according to the results of synchrotron X‐ray diffraction, the local structure exhibits a monoclinic distortion in K _0.4 Mn _0.4 Fe _1.6 Mo ₃ O ₁₂ . In KMnFeMo ₃ O ₁₂ , the local structure still exhibits a hexagonal system. This local distortion affects the coupled rotation of polyhedra and leads to different thermal expansion behaviors. Notably, the KMnFeMo ₃ O ₁₂ exhibits low emissivity in the 1–2.5 µm near‐infrared band. This dual functionality, which includes tunable thermal expansion and near‐infrared (NIR) low emissivity, endows the material with considerable potential for advanced engineering applications.