Switchable K–O bonds unveiling anomalous ferroelastic transitions in a polar hybrid crystal

• Published in: Science China materials 2024-10, Vol.67 (10), p.3408-3414
• Main Authors: Li, Yao-Bin, Xu, Wei-Jian, Chen, Xiao-Xian, Liu, De-Xuan, Wang, Zhi-Shuo, Zhang, Wei-Xiong
• Format: Article
• Language: English
• Subjects: Chemistry and Materials Science; Chemistry/Food Science; Materials Science
• ISSN: 2095-8226; 2199-4501
• DOI: 10.1007/s40843-024-2918-8

Hybrid ferroelastic crystals have garnered considerable interest due to their promising potential as mechanical switches and sensors. The anomalous ferroelastic phase transitions, in which ferroelasticity occurs in the high-temperature phase rather than the low-temperature phase, are of particular interest, but they are sporadically-documented and none of them is involved in breaking of the chemical bonds. Herein, a hydroxyl-containing cation, i.e. , Me 3 NOH + , is employed to construct a three-dimensional hybrid crystal (Me 3 NOH) 2 KBiCl 6 (1). This crystal undergoes distinct two-step structural phase transitions with space-group changes of Pna 2 1 – P 112 1 – P 6 3 mc , belonging to an anomalous temperature-reversed mm 2 F 2 ferroelastic transition and a normal 6 mmF 2 ferroelastic transition, respectively. The anomalous ferroelastic transition is entirely driven by switchable K–O coordination bonds involving breaking and reformation. Notably, the dynamic behavior of Me 3 NOH + cations along with the distortion of inorganic framework enables the manifestation of unusual “high-low-medium” second-harmonic generation-switching behaviors. This study presents the enormous benefits of switchable coordination bonds for inducing anomalous ferroelastic phase transitions, offering valuable insight for the exploration of new multifunctional ferroelastic materials.