Evidence against the polarization rotation model of piezoelectric perovskites at the morphotropic phase boundary

Abstract

The origin of the very large piezoelectric response observed in the vicinity of the morphotropic phase boundary (MPB) in perovskite lead zirconate titanate and related systems has been under intensive studies. Polarization rotation ideas are frequently invoked to explain the piezoelectric properties. It was recently reported that lead titanate undergoes a phase transformation sequence P 4mm → P m → Cm → R3c at 10 K as a function of hydrostatic pressure [M. Ahart et al. Nature Letters. 451, 545 (2008)]. We demonstrate that this interpretation is not correct by (i) simulating the reported diffraction patterns, and (ii) by density-functional theory computations which show that neither the P m, Cm nor P mm2 phase is stable in the studied pressure range, and further show that octahedral tilting is the key stabilization mechanism under high pressure. Notes on a more general ground are given to demonstrate that a continuous phase transition between rhombohedral and tetragonal phases via intermediate monoclinic phase is not possible. Thus, twophase co-existence in the vicinity of the phase transition region is probable and has an important role for electromechanical properties.

Strain on ferroelectric thin films

“…Among the numerous interesting results in this field, a high-pressure form of ferroelectricity has been calculated and observed in PbTiO 3 [59,60] at room temperature. At low temperature and still for PbTiO 3 , a monoclinic phase was calculated [69] and then observed [61], even though this last result and its implication have been questioned [63]. The rotation of the oxygen octahedra as a pressure-accommodating mechanism [70] is a common feature of the observations on lead titanate, as well as for Pb(Zr 1-x Ti x )O 3 .…”

“…From lead zirconate [55][56][57][58] to lead titanate [59][60][61][62][63] through several intermediate compositions [64][65][66][67][68], PZT has been studied under pressure. Among the numerous interesting results in this field, a high-pressure form of ferroelectricity has been calculated and observed in PbTiO 3 [59,60] at room temperature.…”

Recent Advances in Processing, Structural and Dielectric Properties of PMN-PT Ferroelectric Ceramics at Compositions Around the MPB

“…Exploring theoretical predictions and experimental results for the similar MPB in the pure lead titanate PbTiO 3 , which appear under high hydrostatic pressure and cryogenics temperatures leading to tetragonal → monoclinic → rhombohedral phase transition, a more general idea of the morphotropic phase boundary could be introduced with perspectives of developing new high-performance electromechanical materials based on the chemical pressure idea (Ahart et al, 2008). In addition to these very attractive possibilities, observation of a low-symmetry monoclinic phase in the PbTiO 3 opened very recent discussions on the arguments that justify the origin of morphotropic phase boundaries in ferroelectrics (Ahart et al, 2008) and arguments against the validity of the rotation polarization model to describe the stability of the phases and the sequence of phase transformation in the MPB in pure PbTiO 3 (Frantti et al, 2008). This controversy is very interesting because the discussions illustrate how different ideas promote the advancement of science, showing the richness behind the research in phase transitions of systems that exhibit the MPB and that this subject is still open to new contributions.…”

Origin of the large piezoelectric activity in(1−x)Ba(Zr0.2TiAcosta1, Khakpash2, Someya3 et al. 2015Phys. Rev. B1319830View full textAdd to dashboardCite

“…In other ferroelectric solid solutions, the role played by monoclinic (M) phase(s) [16,17], disorder in the displacement of cations [18,19], formation of nanodomains [20,21], and two-phase coexistence [22,23] have been invoked to explain enhanced functional properties near phase boundaries. Despite the differing interpretations of the structural state near phase boundaries, it has been argued that a reduction in the crystalline anisotropy of polarization, as recognized in the earliest studies of PZT, is the central phenomenon connected with large piezoelectric activity [24,25].…”