The influence of operating conditions on properties of lead zicronate titanate and (1-x)[lead magnesium niobate]-(x)[lead titanate] ceramics

The primary goal of the present thesis is to address issues related to the application of ferroelectric ceramics in electromechanical actuators and transducers. Specifically, the electromechanical properties of two types of ferroelectric materials, piezoelectric PZT ceramics and electrostrictive relaxor ferroelectric PMN-PT ceramics, are investigated as a function of electrical and mechanical boundary conditions. In addition, PMN-PT relaxor ferroelectrics are studied with a special focus on the understanding of the mechanism of polarization response of these materials.; The properties of several PZT piezoceramics under stresses were characterized. It was observed that compressive stresses have a marked effect on the soft PZT, including reducing the piezoelectric coefficients and depoling the sample at relatively low stress levels. The effect of the stresses on hard PZT ceramics is more complicated because the domain structure of the materials can be changed substantially without depoling the samples.; The properties of (1-x)PMN-xPT with PT content within 30% was investigated. Exceptionally high induced piezoelectric response was observed, which is d₃₃ = 1820 pm/V at a frequency of 1kHz for 0.8PMN-0.2PT composition.; The volumetric electrostrictive coefficient, $Qh$ of PMN was investigated based on a conventional strain measurements and a high-resolution neutron powder diffraction. Using the results of these experiments we: (1) support the notion that at the temperature near $Tmax,$ which is the temperature of dielectric constant maximum, the polarization response from the nanopolar region is through the polar reorientation; (2) derive the value of $Qh$ of prototype cubic lattice of PMN, which is equal to $Qh=8.3\pm 0.1\times 10-2m4/C2.$; The influence of the compressive stresses on the properties of 0.9PMN-0.1PT near $Tmax$ was investigated. The results reveal that the compressive stress $T3,$, which is applied parallel to the direction of induced polarization, has the effect of favoring the micro-polar state in the material, which is similar to shift the $Tmax$ of material to lower temperature. On the other hand, compressive stress $T1,$ which is applied perpendicular to the direction of induced polarization, has the effect of favoring the macro-polar state in the material, which is similar to shift the $Tmax$ to higher temperature.