electrostrictive actuators are large capacitors with the added complexity of having to perform mechanically as well as electrically. High operating fields and severe operating conditions make it necessary to predict and liimit stress levels generated in the device. A constitutive three-dimensional model for electrostrictors has been develoiped and implemented as a design tool for actuators. The effects of electrode geometry and transition-layer thickness on stress levels have been modeled and failure in high-stress regioins has been correlated with the presence of flaws (pores andl delaminations) in the devices. [

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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.]

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