Emergence of Perovskite (MAPI) phases upon little compression

Perovskites are among the most promising and versatile class of candidate compounds for new or improved materials in energy applications, including photovoltaics, superconductivity, and lasing. With the general formula ABX3, the perovskite structure consists of corner-sharing BX6 octahedra forming a three-dimensional (3D) framework that provides room for the A units in the resulting cuboctahedral cavities.

In our latest work we use classical interatomic potential and coupled with minima hopping method to screen the potential energy surface using simulation cells containing 2, 4, and 8 units (i.e., 24, 48, and 96 atoms), on were more than 140,000 structures were generated.

We also investigated how pressure affects the enthalpy and volume of the experimental and predicted phases of MAPI with respect to the orthorhombic phase (see figure). Based on our careful analysis of the available literature work, none of the experimental high-pressure experiments used the low-temperature orthorhombic phase as the starting material. Instead, our simulated XRD patterns show that the tetragonal phases is present in the samples of experimental work. Based on our calculations, we therefore suggest that either the delta or double delta phases could be synthesized by compressing precursor samples in the orthorhombic (Pnma) phase in low-temperature compression experiments. Since the orthorhombic phase is strongly destabilized upon compression, a transition towards the double-delta or delta phases will be rapidly favored with increasing pressure. Our work is now published in “Phys. Rev. Materials 2, 085201 2018″.