Pressure-induced phase transition in the technologically important tetragonal phase of PbTiO$_3$ has been quite controversial with two entirely different propositions: (1) morphotropic phase boundary-like structural transition with concomitant rotation of the ferroelectric polarization vector and (2) antiferrodistortive (AFD) phase transition followed by emergence of a reentrant ferroelectric phase. We have attempted to address these controversies by enhancing the AFD instability of PbTiO$_3$

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... rough 50% BiFeO$_3$ substitution in a tetragonal composition of the (1−x)PbTiO$_{3−x}$BiFeO$_3$ solid solution system. Using a high resolution synchrotron x-ray diffraction study of the pressure-induced phase transition in this composition, we present here experimental evidence for the emergence of superlattice reflections at a moderate pressure p$_{c1}$∼2.15 GPa due to an AFD transition leading to a monoclinic phase in the Cc space group, which permits the rotation of the ferroelectric polarization vector. We also present evidence for a reentrant ferroelectric phase above p$_{c2}$∼7GPa in which octahedral tilting provides an efficient mechanism for accommodating volume reduction. The implications of these findings in resolving the existing controversies in PbTiO$_3$ and in providing insight for designing environmentally friendly Pb-free piezoelectric compositions are also discussed.