Antiferroelectric and antiferrodistortive phase transitions in Ruddlesden-Popper Pb2TiO4 from first-principles

Abstract

This work employed density functional theory to investigate the structural and ferroelectric properties of the Ruddlesden-Popper (RP) phase of lead titanate, <TEX>$Pb_2TiO_4$</TEX>, as well as its phase transitions with epitaxial strain. A wealth of novel structural instabilities, which are absent in the host <TEX>$PbTiO_3$</TEX> material, were identified in the RP phase through phonon soft-mode analysis. Our calculations showed that the ground state of <TEX>$Pb_2TiO_4$</TEX> is antiferroelectric, distinct from the dominant ferroelectric phase in the corresponding host material. In addition, applied epitaxial strain was found to play a key role in the interactions among the instabilities. The induction of a sequence of antiferroelectric and antiferrodistortive (AFD) phase transitions by epitaxial strain was demonstrated, in which the ferroic instability and AFD distortion were cooperative rather than competitive, as is the case in the host <TEX>$PbTiO_3$</TEX>. The RP phase in conjunction with strain engineering thus represents a new approach to creating ferroic orders and modifying the interplay among structural instabilities in the same constituent materials, enabling us to tailor the functionality of perovskite oxides for novel device applications.