Preparation And Properties Of Sm-PMN-PT/P(VDF-TrFE) Composite Piezoelectric Materials

In our surroundings,there are various mechanical energy,such as noise in the environment,vibration of objects,human activities and so on,so finding effective means to convert it into the electrical energy has become a research hotspot today.Inorganic-organic piezoelectric energy harvesters stand out among piezoelectric energy harvesters due to their combined advantages of inorganic and organic materials.In general,material selection and structural design are the main factors to affect the performance of piezoelectric energy harvesters.In this paper,based on sandwich structure design,the performance of piezoelectric energy harvesters is further improved by selecting inorganic materials with different properties.Among many inorganic piezoelectric materials,lead based piezoelectric ceramics have been widely studied by researchers due to their advantages of high piezoelectric coefficient and good mechanical properties.Polyvinylidene fluoride（PVDF）and its copolymers have become the focus of organic materials research because of their high flexibility,good temperature stability,biocompatibility and other advantages.In this paper,the high performance Pb_0.97Sm_0.02((Mg_1/3Nb_2/3)_0.69Ti_0.31)O₃（Sm-PMN-PT）ceramics are synthesized by the traditional solid-state method,and are combined with polyvinylidene fluoride-trifluoroethylene（P（VDF-TrFE））to prepare piezoelectric energy harvesters.The microstructure,crystal structure and electrical properties of the composite film are systematically studied.In order to improve the problem that the piezoelectric composite film cannot be fully polarized due to the dielectric constant mismatch between the inorganic phase and the organic phase,the conductive filler silver nanowires（Ag NWs）are introduced to further improve its performance.The specific research contents and results are as follows:1.Sm-PMN-PT piezoelectric ceramics are prepared by two-step solid-state sintering method.The effects of different sintering temperatures on ceramic properties are investigated.The optimum sintering temperature is 1250°C,and the corresponding d₃₃ value is 1065 p C/N.The optimum ball milling process for grinding ceramic powder is also investigated,the mixing ratio of large ball（9 mm）,medium ball（6 mm）and small ball（3 mm）is 1:1:1,the speed of ball mill is 235 r/min and the grinding time is2 h,the D₅₀ of the ceramic powder is 0.4μm in the end.2.The prepared piezoelectric ceramic powder is used as filler,polymer P（VDF-TrFe）as matrix,and the film is formed by solvent casting method（solution casting method）.The effect of different contents of ceramic powder on the properties of composite film is investigated.With the increase of powder content,the properties of the composite film showed a trend of first increasing and then decreasing.This is mainly because the crystalβphase in the matrix and the piezoelectric direction of the crystal in the ceramic powder are consistent,which plays an enhanced role in the improvement of the properties.However,if the content of powder is too high,it will easily make the powder aggregate in the matrix and lead to the degradation of performance.Among them,when the content of powder is 15wt%,the frequency is 1Hz and the amplitude is 4 mm,the open-circuit voltage is 53.5 V,which is about 3 times higher than the voltage（17 V）of pure P（VDF-TrFE）.After calculation,the maximum instantaneous power density is 4.96μW/cm².3.In order to improve the insufficient polarization of ceramic powder in the composite film,the conductive filler Ag NWs are introduced to further improve the performance of the composite film.The experimental results show that adding appropriate amount of Ag NWs can obviously improve the performance of composite membrane.This is mainly because on the one hand,it provides a conductive path in the polymer matrix to enhance the polarization performance of composite film,on the other hand,Ag NWs has a large aspect ratio,which is conducive to the dispersion of ceramic powder in the matrix.However,if the content of Ag NWs is too high,the breakdown field strength of composite film will be reduced and the performance will degrade.Among them,the performance of 0.1%Ag NWs/15%Sm-PMN-PT/P（VDF-TrFE）composite film is the best,and its open-circuit voltage is 83.5 V measured at the frequency of 1 Hz and the amplitude of 4 mm,which is 1.6 times higher than that of undoped（53.5 V）.The maximum instantaneous power density is 7.48μW/cm².4.Practical analysis of the piezoelectric energy harvester prepared in this work,and the influence of different types of human mechanical activities such as percussion,bending and pressing is also studied.And connected with bridge rectifier circuit,can directly light up a number of commercial LED lights.