Studies Of Ferroelectric And Piezoelectric Properties Of Sm-doped PMN-PT Ceramics

Relaxor possesses excellent dielectric and piezoelectric properties and thus is widely applied in transducers,acuators and so on.However,the micro-mechanism of the depolarization behavior of relaxor and the influence of ac drive field to the electric properties of ceramic are still unsettled.0.29,0.30 and 0.31)ceramics were prepared by an improved Swartz and Shrout solid-phase two-step synthesis method,with excellent dielectric and piezoelectric properties(d₃₃>970p C/N,?_r>12000).At x=0.28,d₃₃=1310 p C/N,?_r=18400,tan?=0.056 and k_p=0.65.In order to explore the micro-mechanism of the depolarization behavior,phase structure,dielectric,piezoelectricity and ferroelectric properties of 0.025Sm-PMN-x PT ceramics were studied as a function of temperature.It is found that the strongest macroscopic polarization occurs in the corresponding temperature T_iof maximum?35?f/f_r??35?f=f_a-f_r?.With the increasing of temperature,the macroscopic polarization decreases but?_r,frequency dispersion and tan?increase.T_iof the sample with x=0.28,0.29 is near room temperature?RT?,and they exhibit strongest piezoelectricity at RT.From the corresponding temperature T_rof minimum resonant frequency f_r,tan?decreases and P_rdecreases faster.And?35?f/f_rdecreases rapidly When the temperature approaches the corresponding temperature T_dof minimum anti-resonant frequency f_a.Combining the above experimental results,it can be inferred that the depolarization occurs at T_rand ends at T_d,which includes two stages:decoupling of micro-domains and disordering of nano-domains.To investigate the influence of ac drive field to electric properties,the dielectric property of 0.025Sm-PMN-x PT ceramics as a function of temperature under different ac drive field E_acand frequencies f,and field induced strain curve?S-E curve?are measured.According to the measurements,increased E_acwill make T_dand T_mdecrease,but also make?_rand frequency dispersion increase.With the increasing f,T_dremains unchanged and T_mdecreases under the same E_ac.Within a cycle of S-E curve,the hysteresis is small.All of this results show that 1)the pinning effect of domain walls is weak;2)the amplitude of the weak ac drive field is much smaller than the coercive field,but it makes the micro-domains easy to split into nano-domains;3)Sm-PMN-PT ceramics are easy to depolarize which makes them not suitable for strong ac electric field or high temperature applications.To study the field-induced strain characteristic of Sm-PMN-PT ceramics and their application effects as an actuator,the hysteresis loop,unipolar and bipolar electric field-induced strain curve were investigated,and the large electric field-induced strain micro-displacement actuators were fabricated.The test results show that the strain of Sm-PMN-PT ceramics is very large,up to 0.116%,and normalized S_max/E_maxis up to 1150pm/V with small hysteresis.The longer stack length makes the larger output displacement when field-induced strain micro-displacement actuator fabricated by 0.025Sm-PMN-0.28PT ceramic.Under the best condition,the displacement of the actuator with the length of 26.24mm can reach 14.25?m under 1 k V drive field at RT,and its hysteresis is only 0.045‰.The whole study presents 1)Sm-PMN-PT ceramics are excellent candidates for fabricating field-induced strain micro-displacement actuator;2)actuators based on those ceramics possess large displacement output,small hysteresis and good repeat stability.