Regensburg 2007 – wissenschaftliches Programm

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DF: Fachverband Dielektrische Festkörper

DF 9: Electric, Electromechanical and Optical Properties I

DF 9.1: Hauptvortrag

Donnerstag, 29. März 2007, 10:00–10:40, H48

Electric Field Induced Critical Points and Electromechanical Response in Relaxor Ferroelectrics — •Zdravko Kutnjak¹, Robert Blinc¹, Jan Petzelt², and Stanislav Kamba² — ¹Jozef Stefan Iinstitute, Ljubljana, Slovenia — ²Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic

The giant electromechanical response in ferroelectric relaxors such as Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) is of great importance for a number of ultrasonic and medical applications as well as in telecommunications. Despite intensive research the origin of this effect is however still not fully understood.

On the basis of dielectric, heat capacity, and piezoelectric investigations on PMN-PT crystals of various PT compositions we show the existence of a line of critical points for paraelectric to ferroelectric transformation in the composition–temperature–electric field (x-T-E) phase diagram [1]. This line effectively terminates a surface of first order transitions. Above this line supercritical evolution has been observed.

On approaching the critical point both the enthalpy cost to induce the intermediate monoclinic states decrease significantly. It is shown that the critical fluctuations in the proximity of the critical points are directly responsible of the observed enhancement of the electromechanical response in PMN-PT system [1]. Preliminary results of critical phenomena observed in other relaxor systems will be presented [2].

[1] Z. Kutnjak, R. Blinc, J. Petzelt, Nature vol. 441, 956 (2006)

[2] W. Kleemann et al., Phys. Rev. Lett. vol. 97, 065702 (2006)