Almost every material expands when heated. Well-known examples include railroad tracks and concrete roadways, which feature visible expansion gaps to accommodate this effect. However, thermal expansion poses a far more acute challenge for extremely precise technologies, such as lasers and semiconductor manufacturing equipment, where even minute dimensional changes can compromise precision.
Scientists have long sought to develop materials that maintain dimensional stability across a wide temperature range.
Now, a team led by Prof. LIN Zheshuai from the Technical Institute of Physics and Chemistry (TIPC) of the Chinese Academy of Sciences (CAS) has successfully designed a material with an exceptionally broad zero-thermal-expansion temperature window.
The study was published in Nature Chemistry on June 16.
The core challenge in creating an ideal zero-thermal-expansion material (ZTM)—one that is isotropic, stable over a broad temperature range, and physicochemically robust—lies in balancing the forces driving positive thermal expansion against those driving negative thermal expansion (contraction) to achieve a net zero effect. Unfortunately, at elevated temperatures, atomic vibrations responsible for positive thermal expansion intensify and readily overpower the mechanisms behind negative thermal expansion. Consequently, most isotropic ZTMs function only within a narrow window, typically below 400 K (~127 °C).
To overcome this limitation, the researchers grew isotropic optical crystals using a "fractional occupancy and flexible regulation" strategy. Specifically, they introduced partially occupied atomic groups into a closed sodalite-like crystal structure to enhance its flexibility. This design allows the groups within the cages to dynamically adjust the internal cavity spaces, thereby preserving the inward-pulling atomic vibrations that drive negative thermal expansion even at high temperatures.
This strategy was demonstrated in a cubic sodalite-cage crystal. Experiments revealed that the crystal maintains nearly perfect isotropic zero-thermal-expansion behavior across a record-breaking temperature range of 11 K to 893 K (~−262 °C to 620 °C).
Furthermore, the crystal exhibits transparency from the deep ultraviolet to the near-infrared spectral region, with optical properties showing significantly lower temperature dependence than conventional optical materials. This means that optical devices fabricated from this crystal can sustain stable performance even under drastic temperature fluctuations.
According to the researchers, this work not only delivers an advanced optical crystal material for extreme thermal environments, but also establishes a general structural engineering strategy for the rational design of ultra-low thermal expansion materials operating over wide temperature ranges.
This research was supported by the National Key Research and Development Program, the National Natural Science Foundation of China, and relevant programs of CAS.
