The "ferros" of MAPbI(3): ferroelectricity, ferroelasticity and its crystallographic foundations in hybrid halide perovskites

Hybrid halide perovskites have been identified as an important novel class of photovoltaic absorbers and have proven their great potential with ever record-breaking efficiencies. Some of the more fundamental properties of halide perovskites, however, still are to be properly understood. The ongoing debate as to whether ferroelectricity and/or ferroelasticity play a role in these materials is just one example for this. Herein, I aim to make these phenomena more approachable to the wider research community and elucidate the foundations and consequences of these phenomena.