Origin of morphotropic phase boundaries in ferroelectrics

Abstract

A piezoelectric material is one that generates a voltage in response to a mechanical strain (and vice versa). The most useful piezoelectric materials display a transition region in their composition phase diagrams, known as a morphotropic phase boundary, where the crystal structure changes abruptly and the electromechanical properties are maximal. As a result, modern piezoelectric materials for technological applications are usually complex, engineered, solid solutions, which complicates their manufacture as well as introducing complexity in the study of the microscopic origins of their properties. Here we show that even a pure compound, in this case lead titanate, can display a morphotropic phase boundary under pressure. The results are consistent with first-principles theoretical predictions, but show a richer phase diagram than anticipated; moreover, the predicted electromechanical coupling at the transition is larger than any known. Our results show that the high electromechanical coupling in solid solutions with lead titanate is due to tuning of the high-pressure morphotropic phase boundary in pure lead titanate to ambient pressure. We also find that complex microstructures or compositions are not necessary to obtain strong piezoelectricity. This opens the door to the possible discovery of high-performance, pure-compound electromechanical materials, which could greatly decrease costs and expand the utility of piezoelectric materials.

Nanoscale Structure and Mechanism for Enhanced Electromechanical Response of Highly Strained BiFeO3 Thin Films

“…[4] Recently, it has been observed that MPB-like features can also exist in appropriately strained, chemically simple materials. [5,6,7] For instance, it has been shown that BiFeO 3 , which possesses a strong electrical polarization (~90-100 μC/cm 2 ) and is a candidate for the replacement of lead-based ferroelectrics, [8,9] can exhibit a strain-induced structural phase transition which gives rise to enhanced electromechanical response. [7] Using epitaxial thin film growth, X-ray reciprocal space mapping (RSM), atomic (AFM) and piezoresponse (PFM) force microscopy we report the nanoscale structural evolution of such strain-induced phase boundaries in BiFeO 3 .…”

First-principles studies of lone-pair-induced distortions in epitaxial phases of perovskiteSnTiO3andPbTiO3

“…It is remarkable that a single family of PbTiO 3 based perovskite materials, such as lead zirconate titanate PbZr 1−x Ti x O 3 (PZT) [1][2][3][4] and a variety of lead-based relaxor ferroelectrics, 1,5,6 is dominating the field of ferroelectric (FE) and piezoelectric applications. Outstanding polar, piezoelectric and dielectric properties of all of these compounds emanate from strong lattice distortions -specifically, large displacements of both Pb 2+ and Ti 4+ ions away from their centrosymmetric positions in the undistorted perovskite structure.…”

Structural properties of PbVO3perovskites under hydrostatic pressure conditions up to 10.6 GPa

“…Applying chemical pressure by atom substitution may reduce the pressure of the phase boundary to ambient pressure. For example, high electromechanical coupling in PbTiO 3 -PbZrO 3 and PbMg 1/3 Nb 2/3 O 3 -PbTiO 3 solid solutions results from B-site substitution in PbTiO 3 , which tunes the morphotropic phase boundary from high pressure to ambient pressure [13]. The ferroelectric transition in PbVO 3 perovksite exhibits a broad pressure range for the two coexisting phases and is reversible.…”

“…As a result, the PbVO 3 T-phase is stable over a wide range of temperatures, up to its oxidation temperature of 570 K [7]. ABO 3 -type ferroelectric (FE) compounds with perovskite structures often transform to a paraelectric (PE) phase when the temperature or pressure changes [11][12][13]. For instance, the PbTiO 3 tetragonal perovskite (P4mm) transforms to cubic perovskite (Pm3m) at a high temperature of 763 K or at a high pressure of 11.2 GPa [14,15].…”