Organic ferroelastic enantiomers with high Tc and large dielectric switching ratio triggered by order-disorder and displacive phase transition

Molecular-based ferroelastics with dielectric switching properties are highly desirable for their applications on microelectronic dielectric switches, sensors, data storage, and so on. However, the current reports mostly focus on organic-inorganic hybrids containing toxic heavy metal atoms, and the relatively low phase transition temperature limits their application. In this paper, low-toxic organic salt ferroelastic enantiomers (R/S)-4-fluoro-1-azabicyclo[3.2.1]octonium chloride [(R/S)-F-321] were designed and synthesized under the introducing chirality strategy. They undergo a 432F422-type ferroelastic phase transition with a high Curie temperature (Tc) of 470 K, simultaneously exhibiting excellent dielectric switching characteristics. In addition to the ordered-disordered movement of cations, the significant displacement of anions is also responsible for such high Tc and large dielectric switching ratios, which is very rare in molecular-based switching materials. This work enriches the development of molecular ferroelastic switching materials and gives inspiration for the exploration of environmentally friendly high Tc organic salt ferroelastics with prominent switching performances.