Origin of Ferroelectricity in Two Prototypical Hybrid Organic-Inorganic Perovskites

Hybrid organic-inorganic perovskite (HOIP) ferroelectrics are attracting considerable interest because of their high performance, ease of synthesis, and lightweight. However, the intrinsic thermodynamic origins of their ferroelectric transitions remain insufficiently understood. Here, we identify the nature of the ferroelectric phase transitions in displacive [(CH3)(2)NH2] [Mn-(N-3)(3)] and order-disorder type [(CH3)(2)NH2][Mn(HCOO)(3)] via spatially resolved structural analysis and ab initio lattice dynamics calculations. Our results demonstrate that the vibrational entropy change of the extended perovskite lattice drives the ferroelectric transition in the former and also contributes importantly to that of the latter along with the rotational entropy change of the A-site. This finding not only reveals the delicate atomic dynamics in ferroelectric HOIPs but also highlights that both the local and extended fluctuation of the hybrid perovskite lattice can be manipulated for creating ferroelectricity by taking advantages of their abundant atomic, electronic, and phononic degrees of freedom.

Automated summary

In this study, the nature of ferroelectric phase transitions in hybrid organic-inorganic perovskite ferroelectrics was investigated through structural analysis and lattice dynamics calculations. It was found that the vibrational entropy change of the lattice, along with the rotational entropy change, plays a crucial role in the ferroelectric transition, suggesting that both local and extended lattice fluctuations can be manipulated to create ferroelectricity.