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