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Methylammonium lead iodide, as related organometal halide perovskites,emerged recently as a particularly attractive material for photovoltaicapplications. The origin of its appealing properties is sometimes assigned toits potential ferroelectric character, which remains however a topic of intensedebate. Here, we rationalize from first-principles calculations how the spatialarrangement of methylammonium polar molecules is progressively constrained bythe subtle interplay between their tendency to bond with the inorganicframework and the appearance of iodine octahedra rotations inherent to theperovskite structure. The disordered tetragonal phase observed at roomtemperature is paraelectric. We show that it should a priori becomeferroelectric but that iodine octahedra rotations drive the system toward anantipolar orthorhombic ground state, making it a missed ferroelectric.

Missed ferroelectricity in methylammonium lead iodide