TY - JOUR

T1 - Electrocaloric effect in relaxor ferroelectrics

AU - Pirc, R.

AU - Kutnjak, Z.

AU - Blinc, R.

AU - Zhang, Q. M.

N1 - Funding Information:
This work was supported by the Slovenian Research Agency through Grants P1-0044, P1-0125, P2-0105, J1-0155, and J1-2015. Research at the Pennsylvania State University was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Science and Engineering under Award No. DE-FG02-07ER46410. The authors are grateful to Y. Ishibashi for discussions and comments on the manuscript.

PY - 2011/10/1

Y1 - 2011/10/1

N2 - A theoretical model for the electrocaloric effect (ECE) in relaxor ferroelectrics is presented. By solving a self-consistent relation for the ECE temperature change T and minimizing numerically the mean field free energy for relaxors, the field and temperature dependence of T is calculated. The corresponding harmonic Landau coefficient a = a (T), which differs from the ferroelectric case by always being positive, is derived from the spherical random bond-random field model, and the fourth-order coefficient b is treated as a phenomenological parameter, which can be either positive or negative. For b < 0, a line of field-induced first-order relaxor-to-ferroelectric phase transitions exists in relaxors, which terminates at a liquid-vapor type critical point ECP, TCP. The critical behavior close to E CP, TCP is analyzed. It is shown that near the first-order phase transition a temperature or field interval or gap formally appears, where T cannot be found. However, domain formation in the coexistence range should restore the continuous behavior of the ECE observed in real systems. Finally, it is shown that the ECE responsivity R 1 = T / E reaches a maximum near the critical point, in agreement with recent experiments.

AB - A theoretical model for the electrocaloric effect (ECE) in relaxor ferroelectrics is presented. By solving a self-consistent relation for the ECE temperature change T and minimizing numerically the mean field free energy for relaxors, the field and temperature dependence of T is calculated. The corresponding harmonic Landau coefficient a = a (T), which differs from the ferroelectric case by always being positive, is derived from the spherical random bond-random field model, and the fourth-order coefficient b is treated as a phenomenological parameter, which can be either positive or negative. For b < 0, a line of field-induced first-order relaxor-to-ferroelectric phase transitions exists in relaxors, which terminates at a liquid-vapor type critical point ECP, TCP. The critical behavior close to E CP, TCP is analyzed. It is shown that near the first-order phase transition a temperature or field interval or gap formally appears, where T cannot be found. However, domain formation in the coexistence range should restore the continuous behavior of the ECE observed in real systems. Finally, it is shown that the ECE responsivity R 1 = T / E reaches a maximum near the critical point, in agreement with recent experiments.

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U2 - 10.1063/1.3650906

DO - 10.1063/1.3650906

M3 - Article

AN - SCOPUS:80055009952

VL - 110

JO - Journal of Applied Physics

JF - Journal of Applied Physics

SN - 0021-8979

IS - 7

M1 - 074113

ER -