Characterization Of Electromechanical Coupling Properties For The Relaxor Ferroelectric Materials Of PMN And NBT-BT6

Due to the piezoelectric effect and electrostrictive effect, ferroelectric materials have beenwidely applied in the micro-electromechanical system （MEMS） as sensors, actuators, energyharvesters, accelerometers, ultrasonic motors, servers, and so on. The research of relaxorferroelectric material in MEMS devices could be useful for modeling and design of newfunctional device, so the accurate characterization of electromechanical coupling performanceof those materials is very important.There are d31, d33, d₁₅three different modes for piezoelectric energy harvesting. At present,the measurement methods for piezoelectric coefficients of ferroelectric materials are mainlydivided into two categories: inverse piezoelectric effect and direct piezoelectric effect. A lotof methods have been develped to measure piezoelectric coefficients d31and d33of relaxorferroelectric materials, however, few reports using direct piezoelectric effect to measurepiezoelectric coefficients d₁₅of relaxor ferroelectric materials are available in literature.Electrostrictive effect is one of the basic electromechanical coupling effects. In term of thesecondary effect, the deformation generated by electrostrictive effect is very small. Fewreports on the electrostrictive properties were available in literature for ferroelectric materials.In recent years, there are great interests in electrostrictive properties in the relaxorferroelectric researches （such as PMN）. However, the electrostrictive properties have not beenreported for the sodium bismuth titanate NBT.In this thesis, we reviewed the research progress and application background offerroelectric materials. Then two different kinds of relaxor ferroelectrics were chosen as theresearch object, and two types of models were proposed to measure the electromechanicalcoupling performances of the relaxor ferroelectrics respectively. The work has good guidingsignificance for development and application of shear mode piezoelectric devices, and designand performance prediction of relaxor ferroelectrics.Commercial PMN relaxor ferroelectrics was chosen to produce a coplanar electrodestructure of piezoelectric cantilever, and the piezoelectric coefficientd15was evaluatedbased on the relationship between electric charge and excitation acceleration. Then94（Na0.5Bi0.5）TiO3-6BaTiO3（NBT-BT6） relaxor thin films were prepared by using metalorganic deposition （MOD）, and the electromechanical coupling properties were characterizedwith different annealing temperatures.（1） Based on the Timoshenko beam theory, a principle model was proposed to establish therelationship between electric charge and excitation acceleration. Using PMN as a target, in quasi-static we applied the direct piezoelectric effect of multilayer cantilever with coplanarelectrode structure to evaluate the piezoelectric coefficientd15. Comparing the results withthe experiments and finite element simulations, the correctness of the model has beenverified.（2） Based on the electrostrictive equation, we studied NBT-BT6thin film. Theelectrostrictive properties of thin films with different annealing temperatures have beencharacterized combining with ferroelectric, dielectric and piezoelectric properties. The effectof annealing temperature on the electrostrictive properties of NBT-BT6thin films has beendiscussed in detail.