Achieving Ultrawide Negative Thermal Expansion up to 1300 K via Structural Flexibility Engineering.

Developing novel open-framework negative thermal expansion (NTE) materials with both a strong NTE effect and a wide temperature range is crucial for thermal expansion control in high‑precision devices. Inspired by the concept of average atomic volume (AAV), continuous regulation of thermal expansion from positive to zero to negative across a broad temperature range was achieved in the RbxMnxLu2- xMo3O12 system through the reverse design of the guest ion extraction process. Guest ion removal effectively enhances lattice flexibility, enabling Rb0.4Mn0.4Lu1.6Mo3O12 to exhibit strong NTE performance (αv = -25.5 × 10-6 K-1) over an ultra-wide temperature range from 100 to 1300 K. A joint study of synchrotron x-ray diffraction, Raman spectroscopy, and first-principles calculations was conducted to investigate the structure, thermal expansion, and NTE mechanism. The coupling rotation between Mn/LuO6 octahedra and MoO4 tetrahedra, excited by the transverse thermal vibrations of oxygen atoms, is responsible for the NTE in RbxMnxLu2- xMo3O12. This work not only provides a wide temperature range NTE compounds, but also gives one way to design NTE with open-framework structure materials.