Study On Pyroelectric Effect Based On Ortho-tetragonal Phase Transition Of Potassium Sodium Niobate Single Crystal

In daily life and production,all kinds of waste heat will be emitted through the combustion of coal and natural gas,which will cause a kind of thermal pollution that deteriorates the global climate and living environment.According to statistics,the waste heat energy generated by the United States in 2019 accounts for more than half of the total energy consumption.In countries with the highest utilization rate of waste heat energy,nearly 33%of heat energy is still wasted,so the collection and utilization of waste heat energy has become an important subject of scientific research.The pyroelectric effect is one of the effective ways to solve this problem.In the six decades of pyroelectric development,lead-containing pyroelectric materials have become the best candidate materials for pyroelectric energy conversion because of their good working stability and excellent pyroelectric performance.However,lead-containing materials are harmful to the environment and harmful to health in the process of preparation and application.In recent years,countries and regions have paid more and more attention to environmental protection and sustainable energy development,and the restrictions on lead-containing materials have become more stringent.Therefore,development has a high High-performance lead-free pyroelectric materials are imminent.Potassium sodium niobate(KNN)-based lead-free piezoelectric material is one of the lead-free materials most likely to replace lead-based materials due to its excellent electrical properties and high temperature stability.This article takes potassium sodium niobate single crystal as the research object,firstly characterizes its phase structure,and uses LCR impedance measuring instrument to test the dielectric temperature spectrum of the sample to obtain the orthogonal-tetragonal phase transition temperature and Curie temperature of the KNN crystal.Provide basis for the selection of temperature zone for pyroelectric test.The samples were subjected to ferroelectric test and strain test to characterize the ferroelectric properties.A quasi-static measuring instrument was used to test the piezoelectric properties,and the evolution curve of the piezoelectric constant with temperature was explored.Next,a pyroelectric test system was built based on the principle of pyroelectric effect and the dynamic current method,and the barium titanate crystal with known specifications was used for calibration,and the spontaneous polarization characteristics inside the KNN crystal were characterized by the controlled variable method.Perform pyroelectric test and data fitting on KNN crystal,select appropriate test parameters after analysis and comparison,and use pyroelectric test system to test.It is found that the pyroelectric coefficient of KNN crystal near the orthogonal-tetragonal phase transition is as high as 4.64×10⁴?C·m^-2·K^-1,with the conditions of high-performance pyroelectric materials,lead-free and non-toxic,has broad application prospects in the field of pyroelectrics.Finally,the EDS energy spectrometer was used to test and analyze the segregation law of this crystal.The pyroelectric properties of KNN crystals with K element components of 0.398,0.411 and 0.427 were tested.Select samples with different piezoelectric constants for the interval 0.41?0.43 for testing,observe their corresponding electrical domain structure characteristics through PLM,and further establish the corresponding relationship between the domain structure of KNN crystal and its pyroelectric performance,analyze its internal physical mechanism,based on the above analysis.Through the addition of polarization,the domain structure is re-arranged in an orderly manner,the performance of the KNN crystal is optimized,and the practical applicability of the potassium sodium niobate single crystal orthorhombic-tetragonal phase transition is enhanced.