Characterization Of The Complete Constants Of [011]_c Poled 0.72Pb(Mg_1/3Nb_2/3)O₃-0.28PbTiO₃ And[111]_c Poled 0.935Pb(Zn_1/3Nb_2/3)O₃-0.065PbTiO₃ Sing

In last two decades,relaxor-based single crystals have received a lot of interests because they have high piezoelectric properties when they are in proximity of the morphotropic phase boundary(MPB).The full matrix constants of piezoelectric materials should be characterized after they are prepared.The people who study the piezoelectric materials can evalualte the property of matetials based on the the characterization results.Then they can improve the property of the prepared piezoelectric materials by modifying the composition and preparation methods.Moreover,the characterization results are necessary to the people who use piezoelectric materials to design acoustic devices.The ultrasonic pulse-echo method and the electric resonance method are widely used to characterize the materials contants of piezoelectric materials.However,multiple samples should be used during the characterization.The most serious shortcoming of the method based on multiple samples is that the characterization result probably be inconsistent.To guarantee the self-consistency of the result,all material constants should be from the same sample.Resonant ultrasound spectroscopy(RUS)is one of the methods which can characterize all material constants only using one sample.The most difficult step during the RUS characterization is identifying sufficient modes from the measured ultrasound spectrum.However,the more modes are needed in the inversion,the wider the measured frequency bandwidth should be.As a result,the mode identification will be more difficult.To overcome this problem,a new RUS scheme is presented in this thesis.In this scheme,the resonance frequencies of a piezoelectric sample under two different boundary conditions are used in the inversion.One boundary condition is that all surfaces of the sample are free.Another is that one surface of the sample is attached with an electrode,and the other surfaces are free.This scheme may double or even multiply the identified resonance frequencies without increasing the measurement bandwidth.Therefore,it can reduce the difficulty of the mode idendification and improve the reliability of the characterization.In this thesis,the elastic and piezoelectric constants of[01 1]c poled Pb(Mg1/3Nb2/3)O3-28PbTiO3(PMN-28PT)and[111c poled Pb(Zn1/3Nb2/3)O3?6.5PbTiO3(PZN-6.5PT)single crystals are determined by the presented RUS scheme in this thesis.The feasibility of the presented RUS scheme is verified.Note that most resonance frequencies are very insensitive the varation of the the dielectric constants.Therefore,they cannot be determined by RUS.However,they can be calculated from the capacities measured by an impedance analyzer.The characterization results are guaranteed because all of them are determined from the same sample.