Competition between Polar and Antiferrodistortive Modes and Correlated Dynamics of the Methylammonium Molecules in MAPbI${}_3$ from Anelastic and Dielectric Measurements

Abstract

The mechanisms behind the exceptional photovoltaic properties of the metallorganic perovskites are still debated, and include a ferroelectric (FE) state from the ordering of the electric dipoles of the organic molecules. We present the first anelastic (complex Young's modulus) and new dielectric measurements on CH${}_3$NH${}_3$PbI${}_3$, which provide new insight on the reorientation dynamics of the organic molecules, and the reason why they do not form a FE state. The permittivity is fitted within the tetragonal phase with an expression that includes the coupling between FE and octahedral tilt modes, indicating that the coupling is competitive and prevents FE ordering. The onset of the orthorhombic phase is accompanied by sharp stiffening, analogous to the drop of permittivity, due to the hindered molecular dynamics. On further cooling, an intense anelastic relaxation process without a dielectric counterpart suggests the reorientation of clusters of molecules with strong antiferroelectric correlations.

arXiv commentaccepted in J. Phys. Chem. Lett

References in corpus (6)

• Atomistic origins of high-performance in hybrid halide perovskite solar cells
• Direct Observation of Dynamic Symmetry Breaking above Room Temperature in Methylammonium Lead Iodide Perovskite
• Tetragonal CH3NH3PbI3 Is Ferroelectric
• Rotational Dynamics of Organic Cations in CH3NH3PbI3 Perovskite
• Non-ferroelectric nature of the conductance hysteresis in CH3NH3PbI3 perovskite-based photovoltaic devices
• Elastic aging from coexistence and transformations of ferroelectric and antiferroelectric states in PZT

Cited by in corpus (4)

• Stability of Cubic FAPbI${}_3$ from X-ray Diffraction, Anelastic, and Dielectric Measurements
• Defining "Giant" Electrostriction
• Influence of Temperature, Pressure and Humidity on the Stabilities and Transitions Kinetics of the Various Polymorphs of FAPbI${}_3$
• Polar or nonpolar? That is not the question for perovskite solar cells