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The phase transitions between the various polymorphs of FAPbI$_{3}$ (FAPI, FA= formamidinium CH(NH$_{2}$)$_{2}^+$) are studied by anelastic, dielectric andX--ray diffraction measurements on samples pressed from $\delta -$FAPI (2Hphase) yellow powder. The samples become orange after application of as littleas 0.2~GPa, which has been explained in terms of partial transformations to theother hexagonal polymorphs 4H and 6H. The phenomenon is discussed in the lightof what is known about the stability of the various polymorphs of hybrid andinorganic perovskites ABX$_{3}$ with large A cations and hence large tolerancefactor $t$. Remarkably, FAPI at room and higher temperature behaves like aperovskite with large $t$, while just below room temperature it behaves like aperovskite with small $t$. The kinetics of the transformations between thepolymorphs is enhanced by small amounts of intercalated water. It seemstherefore worthy to try improving the atomic diffusion and crystallizationduring synthesis, and hence the final photovoltaic performance, throughcontrolled small amounts of water that should be thoroughly removed after asufficiently homogeneous and smooth microstructure is achieved.

Influence of Temperature, Pressure and Humidity on the Stabilities and Transitions Kinetics of the Various Polymorphs of FAPbI$_3$