Preparation And Properties Of KNN/P(VDF-TrFE) Piezoelectric Composites

In recent years,Pb-based piezoelectric ceramics reinforced polymer composites have been widely used in piezoelectric sensors,transducers,medical ultrasonic probes and other electronic devices.However,the heavy metal lead can cause irreversible damage to the environment and human body,which inspires people to explore and develop new lead-free piezoelectric composite materials with green environmental protection characteristics,high dielectric constant,low dielectric loss,large piezoelectric response,excellent energy storage characteristics,good flexibility and fatigue resistance.In this paper,K_0.5Na_0.5NbO₃（KNN）piezoelectric ceramic particles were used as reinforcement and P（VDF-TrFE）（70/30）copolymer was used as the matrix material to prepare KNN/P（VDF-TrFE）composites by hot pressing and casting,and the effects of preparation process,KNN content,surface modification and particle size on its structure and electrical properties were explored.The specific research results are as follows:KNN powder was successfully synthesized by solid phase reaction at 850℃,and KNN/P（VDF-TrFE）bulk composites was prepared by hot pressing method,and the effects of different KNN volume fractions（20vol.%～70vol.%）and hot-pressing temperature（140℃,150℃,160℃）on its microstructure and electrical properties of KNN/P（VDF-TrFE）bulk composites were explored.The increase of KNN content and the increase of hot-pressing temperature can improve the dielectric,piezoelectric and ferroelectric properties of the composite.At a certain hot-pressing temperature,the dielectric constant and piezoelectric coefficient d₃₃ first increase and then decrease with the increase of KNN volume fraction,and the residual polarization intensity increases with the increase of KNN volume fraction,but when the content is increased to a certain amount,the material loss will increase.When the KNN content is constant,the dielectric constant increases with the increase of hot-pressing temperature,the piezoelectric coefficient d₃₃ first increases and then decreases with the increase of hot-pressing temperature,and the residual polarization intensity decreases with the increase of hot-pressing temperature.KNN/P（VDF-TrFE）thin film composites were prepared by casting method,and the effects of different KNN volume fractions（10vol.%～40vol.%）,heat treatment temperature and surface modification of KNN on its structure and electrical properties were studied.The increase of KNN content and surface modification improved the dielectric properties,piezoelectric properties and ferroelectric properties of thin film composites,while the increase of heat treatment temperature reduced the dielectric and ferroelectric properties of thin film composites,and improved their piezoelectric properties.The dielectric constant,piezoelectric coefficient d₃₃ and residual polarization strength of the film composite were the highest when KNN content IV was 40vol.%and coated with polydopamine（Polydopamine,PDA）.At a frequency of 1k Hz,the dielectric constant of 40vol.%Polydopamine（PDA）@KNN/P（VDF-TrFE）thin film composites was 58.9 and the dielectric loss was 1.09;the piezoelectric constant of40vol.%PDA@KNN/P（VDF-TrFE）thin film composites was 31p C/N,which was 11p C/N higher than that of unmodified 40vol.%KNN/P（VDF-TrFE）thin film composites.The residual polarization intensity is 0.116μC/cm²,and the ferroelectric property is better.Nanoscale KNN/P（VDF-TrFE）thin film composites materials was prepared by hydrothermal synthesis reaction,and the effects of different KNN volume fraction（10vol.%～40vol.%）and grain size on the structure and electrical properties of KNN/P（VDF-TrFE）thin film composites materials were explored,and Nanoscale KNN/P（VDF-TrFE）was explored.The electrical properties of the materials have been improved due to the increase of nano-KNN powder content.It is found that KNN powder with nanoscale particle size does not greatly improve the electrical properties of KNN/P（VDF-TrFE）materials.