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Compressive prestress effects on the electrical and mechanical properties of relaxor ferroelectric materials were studied as a function of temperature for several formulations of Pb(Mg1/3Nb2/3)O3‐PbTiO3‐BaTiO3 (PMN‐PT‐BT) ceramics. Experimentally measured polarization and strain, induced by an ac electric field, decreased as compressive stress increased. Effective Young's moduli also were measured under constant dc electric fields. A significant decrease in modulus was observed with increasing field. The prestress and modulus experiments were modeled analytically using a proposed relaxor ferroelectric constitutive law. In general, excellent agreement between the model and experiments was obtained, indicating that the model accurately predicted the coupled behavior of this relaxor ferroelectric material.

Compositional variation within the Pb(MgInNb2,3)03-PbTi03 -(Ba,Sr)Ti03 (hereafter PMN-PT-BT,ST) ternary (6.4% 5 PT% 5 14.1%, 1.25% 5 BT,ST% 5 2.5%) results in major changes in induced strain and hysteresis. For the 1.25% BT family, the increase in strain correlates with an increase in Tma,, while the dielectric loss is uncorrelated with hysteresis and strain. In addition, weakfield aging (which is not reset by application of field) shows little effect on strain and hysteresis for drive fields of > 0.2 MV/m. The vary narrow polarization-field loops (virgin curves nearly indistinguishable from subsequent cycles) show that weak-field permittivity is a good approximation to the high-field permittivity. Although these data clarify the frequency (T,,,,, is linearly dependent on the logarithm of the frequency) effect on weak-field dielectric behavior, they do not directly address the question of meaningful extrapolation of high-field strain with frequency. In particular, the question remains as to whether the high-field permittivity and strain are frequency dependent. In future papers we will address this question by a combination of measurement techniques as functions of frequency. [Key words: lead magnesium niobate, electromechanical properties, dielectric properties, aging, strain.]

Ceramics in the (1 -x)[(l -y)Pb(MgInNbzn)O3 .yPbTi03].xMeTi03 system, where Me is Sr or Ba, exhibit very large electrostrictive strains at reasonable drive fields. However, the optimum use temperature and frequency vary with the particular composition used. As relaxor ceramics, each composition has a broad transition from electrostrictive to partially piezoelectric behavior. The transition temperature (T,) can be roughly determined from strain or polarization properties; however, it can be more quantitatively determined from the effective electromechanical Q . A plot of induced transverse strainhnduced polarization squared (effective Q12) as a function of temperature shows a sharp and unmistakable change in slope-this defines T , . The slope of induced transverse strain/polarization (effective g31) also shows a change in slope at T,, although this is more gradual than that of effective Q . The indicated T, correlates with those found from measurement of strain and polarization. [Key words: lead magnesium niobate, actuator, electromechanical properties, relaxors, strain.]