Phase diagrams, dielectric, and piezoelectric properties of metal-free perovskite thin films: Phase-field simulations

The molecular ferroelectric materials are desirable for their light weight, mechanical flexibility, and low processing temperature. A novel metal-free perovskite [MDABCO](NH4)I3(MDABCO stands for N-methyl-N′-diazabicyclo[2.2.2]octonium) has been discovered recently with high polarization and high phase transition temperature, which is comparable to the inorganic ferroelectric materials such as BaTiO3. However, the comprehensive theoretical understanding of the domain structure and structure–property relationship is still lacking for the molecular ferroelectrics. Herein, the domain morphology and electrical properties of the (111)-oriented [MDABCO](NH4)I3films are explored via the phase-field simulations. The misfit strain-temperature phase diagram is established for (111)-oriented [MDABCO](NH4)I3films through parameter sweep, where the domain morphologies and phase evolutions are investigated. Moreover, the macroscopic dielectric and piezoelectric properties are calculated, showing that these properties can be enhanced with medium tensile strain (~ 2%). We expect these findings to serve as a road map for the design of high-performance metal-free molecular ferroelectric materials.Graphical abstract(a) Phase diagram of the (111)-oriented [MDABCO](NH4)I3films under different temperature and identical in-plane misfit strain; (b) 2-dimentional plot of the calculated piezoelectric coefficient as a function of misfit strain and temperatures.