Order-disorder transition of a rigid cage cation embedded in a cubic perovskite.

The structure and properties of organic-inorganic hybrid perovskites are impacted by the order-disorder transition, whose driving forces from the organic cation and the inorganic framework cannot easily be disentangled. Herein, we report the design, synthesis and properties of a cage-in-framework perovskite AthMn(N), where Ath is an organic cation 4-azatricyclo[2.2.1.0]heptanium. Ath features a rigid and spheroidal profile, such that its molecular reorientation does not alter the cubic lattice symmetry of the Mn(N) host framework. This order-disorder transition is well characterized by NMR, crystallography, and calorimetry, and associated with the realignment of Ath dipole from antiferroelectric to paraelectric. As a result, an abrupt rise in the dielectric constant was observed during the transition. Our work introduces a family of perovskite structures and provides direct insights to the order-disorder transition of hybrid materials.