Domain Engineering And Electromechanical Properties Of Tetragonal Lead Magnesium Niobate-lead Titanate Single Crystals

Relaxor ferroelectric single crystal(1-x)Pb(Mg1/3Nb2/3)O3-Pb Ti O3 has been considered as an exciting breakthrough due to its ultrahigh electromechanical properties.Currently,plentiful and substantial results about PMN-PT single crystal have been carried out.The marcoscopic electromechanical properties and microscopic ferroelectric domain sturctures are two of the most studied topics about PMN-PT,but are rarely studied integratedly.The marcoscopic properties of PMN-PT are determined by its microscopic sturctures.A slight distortion will lead to a remarkable change in marcoscopic properties of PMN-PT crystals with even the same composition which is unfavorable for its study and application.Otherwise,the research of domain mechanism has been explored to the micro/nano scale,but hasn't associated to the macroscopic electromechanical properties,even less modified the domain structure to enhance the properties.To address this issue,the domain structure of tetragonal PMN-0.37 PT single crystal was modified by domain engineering method,and the relation between domain structure and marcoscopic properties was studied.The microscopic dynamic mechanism of how spontaneous polarization influencing the phase transiton,poling,aging,and thermal stability of PMN-0.37 PT single crystal was also investigated.Ferroelectric properties of PMN-0.37 PT single crystal were investigated to analyze the influence of spontaneous polarization switching during poling.It was found that 90° switching is the main mechanism in PMN-0.37 PT single crystals at low frequencies and low field;otherwise,the 180° switching is the dominating one.2 steps 90° switching is favorable in [001]c and [011]c crystals as the 1 step 90° switching in the [111]c crystal.The mechanism changed to 1step 90°/180° switching at high frequency,high temperature,or after fatiguing.The aging and thermal stability of PMN-0.37 PTsingle crystals was studied,and the relation between domain structure evalution and electromechanical properties was analyzed.It was found that single domain state in [001]c poled PMN-0.37 PT single crystals was break down and domain walls were introduced to enhance electromechanical properties,but micro-domains in [111]c poled PMN-0.37 PT crystals merged with each other to form larger domains which lead to a decrease in electromechanical properties.Single domain crystal is vulnerable to the thermal influence,and doesn't benefit from the second poling method.But the electromechanical properties of domain engineered crystals show a better thermal stability and can be enhanced by second poling method.Dielectric properties of PMN-0.37 PT single crystal were investigated to analyze the relation between domain structures and the dielectic response.It was found that the phase transition temperature Tm of PMN-0.37 PT single crystal is dependent on the orientation and poling state: [001]c oriented crystal exhibits the lowest Tm;[011]c and [111]c oriented crystal exhibits 3?10 ? higher Tm due to the complicate domain structures;and poled samples get 2?3 ? higher Tm than unpoled ones.Curie-Weiss fitting indicates the relaxtion behavior of tetragonal crystals is weak.3T domain engineered crystal has the best phase stability.The relation between macroscopic electromechanical properties and microccopic domain structures was investigated under different poling conditions.It was found that the electromechanical properties were enhance while the domain size is reduced by controling the poling time,field,and temperature.The piezoelectric constant 33 d =706 p C/N,the electromechanical coupling factor tk =0.57,33 k =0.77,and dielectric constant33T? =7575 of [111]c poled PMN-0.37 PT single crystal reached the maxima when poled under the field of 20 k V/cm at 150 ? for 60 min.The full tensors of properties parameters of [111]c and [001]c poled PMN-0.37 PT single crystals were carried out.The extrinsic contribution of 33 d is 20%.The results of this work present theoretical mechanism and experimental methods to optimize the electromechanical properties of PMN-PT single crystals.It's a support to the application of PMN-PT in electromechanical devices.