Electric-Field-Induced Strain Properties Of Fe Doped KTN Based On Digital Holographic Interferometry

Piezoelectric devices can realize the mutual conversion of electric al energy and mechanical energy.Actuators,sensors and other piezoelectric devices are used widely in our life today,and play a very important role.Materials with excellent piezoelectric properties are needed to make piezoelectric devices with good application performance,the most widely used material is lead based piezoelectric ceramic.However,lead is harmful to the environment and human health.In the wake of the increasing environmental awareness of people,the research of lead-free materials is becoming more and more important.KTN crystal has large electrostrictive coefficient,tunable phase boundary according to Ta / Nb composition,nanosecond response speed and excellent electro-optic and photorefractive properties.KTN is a lead-free piezoelectric single crystal with great application potential.Digital holography has the advantages of full field measurement,non-contact and real-time observation.It can characterize the spatial distribution of material strain properties,and is very beneficial for the study of the origin of piezoelectric materials.In this study,based on digital holography technology,the electric-field-induced strain propertie of KTN crystal is studied.Firstly,Fe:KTN crystal is grown by top seeded melting method.The dielectric temperature curves of Fe:KTN crystal before and after pretreatment are measured by LCR instrument.The results show the Curie temperature,phase structure at room temperature and polarization state of Fe:KTN crystals after pretreatment.The XRD diffraction spectrum of the crystal is measured and the lattice constants are calculated.The piezoelectric constant of the crystal is measured by quasi-static instrument,and the hysteresis loop is measured by ferroelectric instrument.The ferroelectric domain states before and after pretreatment are observed by polarizing light microscope.Based on the image plane holography theory,a reflective off-axis digital holographic microscope system is realized.The principle of recording and reconstruction of digital holography is introduced,and the holographic image reconstruction process using plane subtraction method and angular spectrum method is given.This paper implements an algorithm of automatic selection of real image spectrum,which is helpful to realize the full automation of digital reproduction.The advantages and disadvantages of two phase unwrapping methods including least square method and branch cutting method are analyzed,and the branch cutting method is selected for phase unwrapping.The monopolar strain curve of Fe:KTN crystal is measured by digital holographic microscope system,and the accuracy of the measurement results is verified by ferroelectric tester.The spatial distribution of electric-field-induced strain in KTN crystal is characterized.The composition distribution of KTN crystal is measured by scanning electron microscope.The relationship between strain and composition is studied and explained theoretically.The temporal evolution of electric-field-induced strain of KTN crystal under DC electric field is measured by digital holography system.The response of crystal domain to DC electric field is observed by polarizing light microscope.The relationship between the strain time evolution and domain structure is analyzed.