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The giant electromechanical response in ferroelectric relaxors as a critical phenomenon


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’1,2,3,4 such as Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT; refs 5, 6): these materials exhibit a giant electromechanical (piezoelectric) response that is finding use in ultrasonic4 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.

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Figure 1: Critical behaviour near the morphotropic phase boundary of PMN-PT.
Figure 2: Variation of the polarization order parameter as function of the electric field and temperature in PMN-PT and pure PMN single crystal.
Figure 3: The E T x phase diagram of the PMN-PT system.
Figure 4: Piezoelectric response and enthalpies related to the polarization rotations.


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This research was supported by the Slovenian Research Agency.

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Correspondence to Z. Kutnjak.

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Kutnjak, Z., Petzelt, J. & Blinc, R. The giant electromechanical response in ferroelectric relaxors as a critical phenomenon. Nature 441, 956–959 (2006).

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