Study On Physical Properties Of Potassium Tantalum Niobate And Lead Niobium Magnesium-lead Titanate Based Ferroelectric Single Crystals

Ferroelectric single crystal materials usually have very high piezoelectric coefficients and electromechanical coupling coefficients,and also have very low dielectric losses and high mechanical quality factors,so they have a wide range of applications in medical ultrasound imagers,underwater acoustic transducers and piezoelectric drivers.This paper investigates the physical properties of potassium tantalum niobate(K(Ta,Nb)O3,KTN)-based single crystals and lead niobium magnesiumate-lead titanate(PMN-PT)single crystals.The structural characteristics,strain characteristics,dielectric properties and piezoelectric properties of KTN single crystals were systematically studied,and the effects of AC polarization on the properties of PMN-PT single crystals with different orientations,different components and Mn doped single crystals were studied.This paper comprehensively tests and analyzes the structure,piezoelectric properties,dielectric properties,elastic properties and electromechanical coupling properties of large size(25*25*37 mm3)KTN single crystal.The full matrix parameters of KTN single crystals were tested by ultrasonic and resonance combination method,and the d15 of KTN single crystal was found to be higher than its d33,showing strong shear piezoelectric performance.Subsequently,the piezoelectric coefficient d33*,electromechanical coupling coefficient k33*and elastic coefficient S33E*are simulated by coordinate transformation in three-dimensional space and(100)C surface,and it is found that the above parameters are maximized along the[001]C direction,indicating that the polarization piezoelectric performance,electromechanical coupling elastic performance and elastic performance of tetragonal phase KTN single crystal along the[001]C direction are optimal.Through the hysteresis loop test,it was found that KTN single crystals had a large internal offset field(Ei),and the Ei was mainly derived from the component gradient.The composition uniformity,full matrix parameters and strain characteristics of Sn:KTN single crystals were comprehensively studied.The electron probe(EPMA)test,energy dispersion spectroscopy(EDS)test,and dielectric temperature spectroscopy test verified that niobium(Nb)elements are uniformly distributed within Sn:KTN single crystals.Testing the full matrix parameters of Sn:KTN single crystals,the coordinate transformation simulates the distribution of ε33T*,d33*,k33*and s33E*in three-dimensional space and(100)C-planes,and finds that the maximum values of all the above parameters are along the[001]C direction.Rayleigh analysis found that the intrinsic contribution of the dielectric response of Sn:KTN single crystal was much higher than the extrinsic contribution.Compare the distribution of d33*of Sn:KTN,KNNLT and KTN single crystals in the(100)c plane,it was found that KNNLT single crystal with room temperature close to orthogonal-tetragonal phase temperature(TO-T)had d15 higher than d33,while Sn:KTN single crystal near Curie temperature(TC)and it’s d33 was higher than d15.This is due to the energy competition between O and T phases greatly favors Ps rotation(corresponds to shear lattice deformation)though flattening the free energy profile along Ps rotation path,so KNNLT shows high d15 and large d15/d33 ratio.Energy competition between T and C phase benefits Ps extension/contraction(corresponds to longitudinal lattice deformation)by flatting the energy along the polarization extension/contraction path,so Sn:KTN shows low d15 and d15/d33 ratio At the same time,the strain curve of Sn:KTN single crystal under the large electric field is also tested,and the domain switch process analyzed.Explore the alternating current poling process of PMN-PT series single crystals and Cu:KNNT lead-free piezoelectric materials,and analyze the reasons for the improvement of single crystal performance caused by alternating current poling through Rayleigh analysis and domain observation.By comparing the alternating current poling effect of[001]C-oriented PMN-26PT,PMN-32PT,Mn:PIN-PMN-PT,Cu:KNNT and[011]C-oriented PMN-26PT single crystal,it is found that alternating current poling can significantly improve the piezoelectric coefficient and dielectric coefficient of[001]C-oriented PMN-PT single crystals,,but can not improve the piezoelectric and dielectric coefficient of[001]C-oriented Cu:KNNT and[011]Coriented PMN-26PT,indicate that alternating current poling polarization has a certain scope of application.Through Rayleigh analysis,it was found that alternating current poling can significantly improve the extrinsic contribution of the dielectric response of PMN-PT single crystals,thereby improving its dielectric performance.The domain structure of the PMN-PT single crystals,after alternating current poling polarization and direct current poling was observed by piezoelectric power microscopy(PFM),and it was found that alternating current poling polarization can make the domains became a regular long strip,and the width of the domains is smaller than the width of the domains after direct current poling.