Effects of frequency, temperature, and dc bias electric field on the dielectric properties of methylammonium lead iodide from the perspective of a relaxor-like ferroelectric

Caution! Static Supercell Calculations of Defect Migration in Higher Symmetry ABX3 Perovskite Halides May Be Unreliable: A Case Study of Methylammonium Lead Iodide

“…Meggiolaro et al used a short molecular-dynamics simulation together with NEB calculations; Tong et al fixed the orientation of the MA + species and calculated barriers for various combinations of MA + orientations; and Azpiroz et al used linear-transit, rather than NEB, calculations (although it is not clear to us why this method gives a different result). Incidentally, these three studies ,, also predict Δ E mig,v values between 60 and 110 meV, in very good agreement with data from MD simulations and with experimental data − for β- and α-MAPbI 3 .…”

“…First, MD simulations with the MYP potentials reproduce with increasing temperature the γ, β, and α phases, including the reorientation barriers of the MA + cations . Second, MD simulations with the MYP potentials of iodine-vacancy diffusion, employing sufficiently large supercells and relatively long run times, yield Δ E mig,v = 0.080 ± 0.004 eV, a value in excellent agreement with experimental transport data for both β and α phases. − The key benefit is that the same set of potentials provides a reference value for Δ E mig,v that refers unambiguously to phases that are stable at those temperatures. Third, by using EPP rather than DFT calculations, we confirm that the problem does not lie with DFT itself but rather in the use of static supercell calculations.…”

Differing Effects of Mixed A-Site Composition on the Properties of Hybrid Lead Iodide Perovskites

“…In Figure a, the abrupt change in both components of dielectric permittivity at around 160 K shows the typical behavior of the orthorhombic-tetragonal ( O → T ) phase transition for the pure MAPbI 3 , associated with the disruption of the cooperative ordering of MA + cations. ,, As for the FA 0.10 MA 0.90 PbI 3 composition, different transitions below 200 K may occur, as observed in Figure b. In the FA x MA 1– x PbI 3 system, several structures and transitions have been proposed in the literature. , It can be argued that the changes in the temperature profile of the dielectric permittivity curves compared to MAPbI 3 are partly due to the possible existence of a large-cell cubic (LC) intermediate phase between the orthorhombic and tetragonal phases .…”

Studies of Structural, Dielectric, and Impedance Spectroscopy of KBT-Modified Sodium Bismuth Titanate Lead-Free Ceramics

“… 89 The broad peak is associated with the cation disorder problem resulting from the random distribution of A and B site cations over the equivalent lattice positions. 90 In these graphs, we can observe the effect of increasing temperature on the value of Z ″. Z ″ increases with frequency and reaches a maximum value at a particular frequency, which is designated as the relaxation frequency.…”