Multi-step structural phase transitions with novel symmetry breaking and inverse symmetry breaking characteristics in a [Ag4I6]2− cluster hybrid crystal
In this study, a multi-step phase transition hybrid comprised of (Pr-dabco)2Ag4I6 clusters (Pr-dabco+ = 1-Propyl-1,4-diazabicyclo[2.2.2]octan-1-ium) has been prepared and characterized by microanalysis, IR and UV-vis spectroscopy, TG and DSC techniques etc. This hybrid thermally stabilizes up to ~486 K with five phases in the temperature region below 486 K. The phase transition shows symmetry breaking (SB) character between phases II (space group P21/c) and III (space group Pa-3), while inverse symmetry breaking (ISB) feature between phases II and I (space group Pbca), and it is rather exceptional that a matter exhibits simultaneously SB and ISB natures in two successive phase transitions. Most importantly, each phase transition is associated with a dielectric anomaly, and phase V features as plastic crystal with extra high ac conductivity (>10-2 S cm-1). Our work opens a way to find multi-phase transition material in silver halide hybrids.