An Unprecedented PF ₆ ^– -Based Pseudohalide Metal-Free Perovskite Ferroelastic

Pseudohalide metal-free perovskites (MFPs) have attracted growing interest in the fields of ferroelectrics, piezoelectrics, X-ray detection, and electro-optic modulation for their lightweight nature, environmental friendliness, mechanical flexibility, and excellent biocompatibility. However, to the best of our knowledge, no PF 6 – -based MFP ferroelastics have been reported to date. In this work, we presented the first PF 6 – -based MFP ferroelastic DABCO-NH 4 (PF 6 ) 3 (DABCO = 1,4-diazabicyclo[2.2.2]octane), which is synthesized using an aqueous solution, distinguishing it from previously reported materials that rely heavily on toxic organic solvents. At 355 K, DABCO-NH 4 (PF 6 ) 3 undergoes a m 3̅ mF 3̅ m type ferroelastic phase transition. Polarized optical microscopy was employed to clearly visualize the ferroelastic domains and their stress-induced dynamic evolution. This work will inspire further exploration of multifunctional pseudohalide metal-free perovskites.