Evidence for pressure-induced polarization rotation, octahedral tilting, and reentrant ferroelectric phase in tetragonal (P b0.5 B i0.5)(T i0.5 F e0.5) O3

Abstract

Pressure-induced phase transition in the technologically important tetragonal phase of PbTiO3 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 PbTiO3 through 50% BiFeO3 substitution in a tetragonal composition of the (1-x)PbTiO3-xBiFeO3 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 pc1∼2.15GPa 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 pc2∼7GPa in which octahedral tilting provides an efficient mechanism for accommodating volume reduction. The implications of these findings in resolving the existing controversies in PbTiO3 and in providing insight for designing environmentally friendly Pb-free piezoelectric compositions are also discussed. © 2019 American Physical Society.