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 Rb x Mn x Lu 2− x Mo 3 O 12 system through the reverse design of the guest ion extraction process. Guest ion removal effectively enhances lattice flexibility, enabling Rb 0.4 Mn 0.4 Lu 1.6 Mo 3 O 12 to exhibit strong NTE performance ( α v = −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/LuO 6 octahedra and MoO 4 tetrahedra, excited by the transverse thermal vibrations of oxygen atoms, is responsible for the NTE in Rb x Mn x Lu 2− x Mo 3 O 12 . This work not only provides a wide temperature range NTE compounds, but also gives one way to design NTE with open‐framework structure materials.