Giant Negative Thermal Expansion in Ultralight NaB(CN)<sub>4</sub>
Qilong Gao, Yixin Jiao, Qiang Sun, Jan A. P. Sprenger, Maik Finze, Andrea Sanson, Erjun Liang, Xianran Xing, Jun Chen
Abstract
Abstract Negative thermal expansion (NTE) is crucial for controlling the thermomechanical properties of functional materials, albeit being relatively rare. This study reports a giant NTE (α V ∼−9.2 ⋅ 10 −5 K −1 , 100–200 K; α V ∼−3.7 ⋅ 10 −5 K −1 , 200–650 K) observed in NaB(CN) 4 , showcasing interesting ultralight properties. A comprehensive investigation involving synchrotron X‐ray diffraction, Raman spectroscopy, and first‐principles calculations has been conducted to explore the thermal expansion mechanism. The findings indicate that the low‐frequency phonon modes play a primary role in NTE, and non‐rigid vibration modes with most negative Grüneisen parameters are the key contributing factor to the giant NTE observed in NaB(CN) 4 . This work presents a new material with giant NTE and ultralight mass density, providing insights for the understanding and design of novel NTE materials.