| With the extensive use of ultrasonic imaging in modern medicine community,the requirements for the performance of ultrasonic transducers,such as bandwidth and sensitivity,are also increasing.The bandwidth and sensitivity of ultrasonic transducers are mainly determined by the piezoelectric and electromechanical properties of the piezoelectric element.Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT),a typical relaxor ferroelectric system,with excellent piezoelectric and electromechanical performance is an important material for the development of ultrasonic transducers.However,its application is restricted by the low Curie temperature and coercive field.In order to overcome these shortcomings,Pb(Sc1/2Nb1/2)O3(PSN)with high Curie temperature is introduced in a binary PMN-PT system to obtain a ternary Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3(PSN-PMN-PT)system in this paper.The phase structure,electrical properties and thermal stability at the composition near morphotropic phase boundary(MPB)of ternary PSN-PMN-PT ceramics is studied.In order to evaluate the application potential of PSN-PMN-PT ceramics in ultrasonic transducers,the ultrasonic transducer is fabricated by PSN-PMN-PT ceramics with excellent comprehensive performance.(1)Based on the linear combination law of the morphotropic phase boundary,xPSN-(1-x-y)PMN-yPT ceramics are prepared by two-step columbite precursor method.The phase structures of the ceramics are studied by XRD.and it is found that the prepared ceramics are all morphotropic phase boundary components.Through the research of the electrical properties of the samples,it is found that the Curie temperature and coercive field increased with the increase of PSN content.Ceramics with x=0.43 and y=0.4 have the highest Curie temperature(253℃)and the largest coercive field(7.63 kV/cm),which are obviously superior to PMN-PT.It is feasible to introduce PSN into PMN-PT to improve Curie temperature and coercive field.And the ceramics with x=0.43 and y=0.4 have the highest piezoelectric constant of 630 pC/N.(2)0.43PSN-(0.57-y)PMN-yPT(y=0.37,0.38,0.39,0.4,0.42)ceramics are prepared by two-step columbite precursor method.The phase structures of ceramics are studied by XRD.It is found that the morphotropic phase boundary compositions are y=0.38-0.4.The electrical properties of ceramics are studied.With the increase of PT content,the Curie temperature and coercive field increased,the piezoelectric constant first increased and then decreased.The y=0.4 ceramics have good electrical properties,the remnant polarization,coercive field,piezoelectric constant,plane electromechanical coupling factor,thickness extensional electromechanical coupling factor,dielectric constant and dielectric loss are 36.82 μC/cm2,7.63 kV/cm,630 pC/N,0.64,0.56,3347,0.007,respectively.Through the study of the thermal stability of the electrical properties of the ceramics at y=0.4,it is found that the piezoelectric constant remains more than 80%of the initial value at 250℃,and the thickness extension electromechanical coupling factor remains more than 95%of the initial value at 240℃.The results above indicate that y=0.4 ceramics have good electrical properties and excellent thermal stability.(3)Based on the Krimholtz-Leedom.Matthae model,the 0.43PSN-0.17PMN-0.4PT ceramics with good comprehensive performance is used as piezoelectric element to design ultrasonic transducer with 5MHz center frequency.PiezoCAD is used to simulate the ultrasonic transducer.The simulated results show that the center frequency of the transducer is 4.64 MHz,and the-6 dB bandwidth is 81.27%.The test results show that the center frequency is 4.86 MHz,the-6 dB bandwidth is 70.5%,and the insertion loss at the center frequency is-22.07 dB.Compared with the PMN-PT single crystal ultrasonic transducer with the same structure and matching layer material,the-6 dB bandwidth of PSN-PMN-PT ultrasonic transducer is wider,which indicates that PSN-PMN-PT ceramics have a certain application potential in ultrasonic transducers. |
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