The giant electromechanical response in ferroelectric relaxors as a critical phenomenon

Abstract

The direct conversion of electrical energy to mechanical work by a material is relevant to a number of applications. This is illustrated by ferroelectric 'relaxors' such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT; refs 5, 6): these materials exhibit a giant electromechanical (piezoelectric) response that is finding use in ultrasonic and medical applications, as well as in telecommunications. The origins of this effect are, however, still unclear. Here we show that the giant electromechanical response in PMN-PT (and potentially other ferroelectric relaxors) is the manifestation of critical points that define a line in the phase diagram of this system. Specifically, in the electric-field-temperature-composition phase diagram of PMN-PT (the composition being varied by changing the PT concentration), a first-order paraelectric-ferroelectric phase transition terminates in a line of critical points where the piezoelectric coefficient is maximum. Above this line, supercritical evolution is observed. On approaching the critical point, both the energy cost and the electric field necessary to induce ferroelectric polarization rotations decrease significantly, thus explaining the giant electromechanical response of these relaxors.

Giant magnetostriction in annealed Co1−xFex thin-films

“…An emerging trend is that magnetostriction enhancement in Fe based systems occurs for compositions near structural phase boundaries. An analogy with giant electrostriction of ferroelectric solid solution and relax ors 22,23 also points to the intriguing possibility that some structural boundaries in magnetic materials can act as property enhancing morphotropic phase boundaries. Indeed, Yang et al have reported a rhombohedral/tetragonal morphotropic phase boundary with enhanced magnetostrictive properties in the TbCo 2 -DyCo 2 sys tem occurring below 160 K (ref.…”

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.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…It is noted, however, that an electric field induced nucleation of an O phase at expense of the T phase 321 or a change in the relative content of R and T phases cannot be discarded. The peak in piezoelectric response observed above marked with indicates that the electric field induced paraelectric to ferroelectric transitions in BZT-BCT are of first order 156,188,191 , which is supported by the non-zero thermal hysteresis in dielectric properties. 194 The high 33 values above that were obtained at finite bias-fields ( 33 ) = (0.40 ± 0.12) kV/mm implies a line of critical points.…”

“…194 The high 33 values above that were obtained at finite bias-fields ( 33 ) = (0.40 ± 0.12) kV/mm implies a line of critical points. [188][189][190][191] This observation casts doubt on the assertion that triple points of the zero-field pseudo-binary phase diagram are also tricritical points. 194,333 In order to allow a better understanding of the strain mechanisms in BZT-BCT, quantification of the intrinsic and extrinsic contributions to 33 .3 is valid with the assumption that reversible switching is considerably reduced at zero bias-field.…”

“…157,187 Some authors extended the concept of a free energy anisotropy further and evoked criticality as the fundamental reason behind enhanced properties. [188][189][190][191] A critical point is defined as a continuous transition from a first order to a second order phase transition under thermodynamic equilibrium that does not involve thermal hysteresis. Near these critical points, the energy barrier for a phase transition is considerably diminished.…”