Preparation Of Lead-free Piezoelectric Materials K_0.5Na_0.5NbO₃ And Research On Composite Film Nanogenerator

Energy harvesting based on piezoelectric effect due to its sustainability and renewability has been widely concerned by researchers.Piezoelectric nanogenerator has superior advantages such as relatively small size,simple fabrication design,long cycle life,work steadily and the environmentally friendly characteristic,piezoelectric power generation is a very promising approach to realize self-powering electronic devices.Although commercial PZT,PMNT and other lead piezoelectric materials have remarkable piezoelectric coefficients,the lead in the materials is a serious threat to human health and the environment.Besides,ZnO,PVDF and other piezoelectric nanogenerator materials or composites,due to the low piezoelectric coefficient limit their further widespread application.Thus,research on nanogenerator using new lead-free piezoelectric materials or composite films based on BTO and KNN has become the focus of research on energy harvesting.Based on this,the pure phase nanomaterials potassium sodium niobate K_0.5Na_0.5NbO₃（KNN）were prepared in this paper.Piezoelectric composite films based on KNN and carbon-based conductive materials were further prepared,the output performance of piezoelectric nanogenerator based on composite film was discussed,the influence of composite film was explored and analyzed.The specific research contents are as follows:（1）KNN nanomaterials were synthesized using solid state reaction technique,and the influence of calcination temperature on the crystal phase and purity of KNN was studied.The results show that:the calcined temperature too low or too high,impure phase would appear in the final products,only at suitable calcined temperature（900℃）,single phase perovskite structure of KNN was synthesized successfully.When the temperature is too low,there are traces of impure phase Nb₂O₅ in the final products.When the temperature is too high,the secondary phase K₂Nb₈O₂₁ is formed in the final products.（2）KNN/PDMS and KNN/PDMS/C flexible composite films were prepared by spin-coating process,and the output performance of the composite piezoelectric nanogenerator was studied.It is found that:in KNN/PDMS composite film,when the concentration of KNN increases,the piezoelectric performance of the piezoelectric nanogenerator will improve;The piezoelectric performance of the piezoelectric nanogenerator will also improve with the increase of the thickness of the composite film.In KNN/PDMS/C composite film,the output voltage of the composite nanogenerator was increased at first and then decreased.When C content is 12 wt%,the voltage reached the maximum value of 10.55 V,which is 3.3 times of the voltage of 3.22 V when C content is 0 wt%.In addition,the dielectric properties and ferroelectric properties of the composite films was investigated.It is found that the change trend of the relative permittivity?_r and the remanent polarization P_r is the same as that of the output voltage,?_r is 173.56（1 kHz）and P_r is 1.84μC/cm² when C content is 12 wt%.（3）KNN/PDMS/rGO composite films were prepared with different contents rGO doping,and the output performance of the composite piezoelectric nanogenerator was studied.It is found that the output voltage of the composite nanogenerator was increased at first and then decreased with the increase of rGO content in the composite film,the rGO threshold is 1.5 wt%,and the maximum output voltage was 6.02 V.In addition,the dielectric properties and ferroelectric properties of the composite films was investigated.It is found that the change trend of the relative permittivity?_r and the remanent polarization P_r is the same as that of the voltage,?_r is 4.47（100 kHz）and P_r is 1.303μC/cm²when rGO content is 1.5 wt%.Finally,a composite piezoelectric nanogenerator is able to light up a commercial green LED through an energy storage capacitor to verify the feasibility of the practical application,and its mechanical reliability and stability are studied by repeated cycling.It is observed that the generated output signals amplitude does not appear to change significantly even after 4000cycles.