  SrAl2Si2 crystallizes into either a semimetallic, CaAl2Si2-type, \alpha phase
or a superconducting, BaZn2P2-type, \beta phase. We explore possible \alpha
--Pc;Tc--> \beta transformations by employing pressure- and
temperature-dependent free-energy calculations, vibrational spectra
calculations, and room-temperature synchrotron X-ray powder diffraction (XRPD)
measurements up to 14 GPa using diamond anvil cell. Our theoretical and
empirical analyses together with all baric and thermal reported events on both
phases allow us to construct a preliminary P-T diagram of transformations. Our
calculations show a relatively low critical pressure for the \alpha to \beta
transition (4.9 GPa at 0 K, 5.0 GPa at 300 K and 5.3 GPa at 900 K);
nevertheless, our nonequilibrium analysis indicates that the
low-pressure-low-temperature \alpha phase is separated from metastable \beta
phase by a relatively high activation barrier. This analysis is supported by
our XRPD data at ambient temperature and P < 14 GPa which shows an absence of
\beta phase even after a compression involving three times the critical
pressure. Finally, we briefly consider the change in Fermi surface topology
when atomic rearrangement takes place via either transformations among
SrAl2Si2-dimorphs or total chemical substitution of Ca by Sr in isomorphous
\alpha CaAl2Si2; empirically, manifestation of such topology modification is
evident when comparing the evolution of (magneto-)transport properties of
members of SrAl2Si2-dimorphs and \alpha isomorphs.
