Ta T (macro-micro) FIGURE 50. 1 Polarization and dielectric behavior of a relaxor ferroelectric as a function of temperature, showing the three temperature regimes. Transverse StrainⅨx,x10 P3(C2/m4 FIGURE 50.2 Transverse strain as a function of the square of the polarization in ceramic 0.9PMN-01PT, at RT. The quadratic (x= QP)nature of electrostriction is illustrated. Shaded circles indicate strain ed while polarization and unshaded circles indicate decreasing polarization Based on dielectric constant vs. temperature plots, the electromechanical behavior of a relaxor ferroelectric may divided into three regimes(Fig. 50. 1). At temperatures less than Ta, the depolarization temperature, the relaxor material is macropolar, exhibits a stable remanent polarization, and behaves as a piezoelectric. Tmax is the temperature at which the maximum dielectric constant is observed. Between T, and Tmax, the material possesses nanometer-scale microdomains that strongly influence the electromechanical behavior. Large dielec tric permittivities and large electrostrictive strains arising from micro--macrodomain reorientation are observed. Above Tmax, the material is a"true electrostrictor"in that it is paraelectric and exhibits nonhysteretic, quadratic strain-field behavior. Since macroscale domains are absent, no remanent strain is observed. Improved repro- ducibility in strain and low-loss behavior are achieved Figure 50.2 illustrates the quadratic dependence of the transverse strain on the induced polarization for ceramic 0.9PMN-0. IPT. Figure 50.a and b show the longitudinal strain as a function of the applied electric ield for the same composition. The strain-field plots are not quadratic, and illustrate essentially anhysteretic nature of electrostrictive strain. The transverse strain is negative, as expected c 2000 by CRC Press LLC© 2000 by CRC Press LLC Based on dielectric constant vs. temperature plots, the electromechanical behavior of a relaxor ferroelectric may divided into three regimes (Fig. 50.1). At temperatures less than Td , the depolarization temperature, the relaxor material is macropolar, exhibits a stable remanent polarization, and behaves as a piezoelectric. Tmax is the temperature at which the maximum dielectric constant is observed. Between Td and Tmax , the material possesses nanometer-scale microdomains that strongly influence the electromechanical behavior. Large dielec￾tric permittivities and large electrostrictive strains arising from micro–macrodomain reorientation are observed. Above Tmax, the material is a “true electrostrictor” in that it is paraelectric and exhibits nonhysteretic, quadratic strain-field behavior. Since macroscale domains are absent, no remanent strain is observed. Improved repro￾ducibility in strain and low-loss behavior are achieved. Figure 50.2 illustrates the quadratic dependence of the transverse strain on the induced polarization for ceramic 0.9PMN–0.1PT. Figure 50.3a and b show the longitudinal strain as a function of the applied electric field for the same composition. The strain-field plots are not quadratic, and illustrate essentially anhysteretic nature of electrostrictive strain. The transverse strain is negative, as expected. FIGURE 50.1 Polarization and dielectric behavior of a relaxor ferroelectric as a function of temperature, showing the three temperature regimes. FIGURE 50.2 Transverse strain as a function of the square of the polarization in ceramic 0.9PMN–0.1PT, at RT. The quadratic (x = QP2 ) nature of electrostriction is illustrated. Shaded circles indicate strain measured while increasing polarization and unshaded circles indicate decreasing polarization. Temperature (°C) Polarization Pa Dielectric constant K Td Tm III (macro-polar) II (macro-micro) I (electrostrictive)