Investigation Of Electromechanical Properties In Manganese Doped PIN-PMN- PT And KNNLST Ferroeletric Single Crystals

Mn-doped Pb(In_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃?PIN-PMN-PT?single crystal has good piezoelectricity,high phase transition temperature and high coercive field,etc.Mn ion doping also improves the mechanical quality factor of single crystal,making this Mn-doped Ternary single crystals can be widely used in scientific research,and are also beneficial for applications in high-power devices,such as high-energy transducers and transformers.However,the presence of lead elements limits the application of traditional lead-containing single crystals.In recent years,with the improvement of people's environmental awareness,the development of new high-performance lead-free piezoelectric materials is very important.Among them,?K,Na?NbO₃-based?KNN-based?materials are considered to be one of the most likely systems to replace traditional lead-based ferroelectric materials.However,the current research is mostly directed to KNN-based ceramic materials,and there are still many gaps in the study of KNN single crystal.In this paper,the electromechanical properties of PIN-PMN-0.27PT:Mn and KNNLST:Mn single crystals were studied,and the high piezoelectric properties of these single crystals were analyzed from the perspective of intrinsic contribution and extrinsic contribution.The high shear piezoelectric properties of PIN-PMN-0.27PT:Mn single crystal polarized along the[011]_C direction were investigated.By comparison with single crystals of other domain structures,we found that this single crystal of"2R"domain structure has good shear piezoelectric properties(d₁₅=1642 pC/N,k₁₅=0.862),second only to single domain structure.Under the external electric field excitation,the shear piezoelectric properties of the"2R"domain structure were not significantly reduced.Below the phase transition temperature,the shear properties maintain good thermal stability.The mechanism of high shear piezoelectric properties was analyzed.It was considered that the[011]_C crystallographic orientation and the lower domain mutual inhibition promote the high shear piezoelectric properties corresponding to the intrinsic and extrinsic contributions,respectively.Considering the"2R"domain structure of PIN-PMN-0.27PT:Mn single crystal has high shear piezoelectric properties,good stability,low dielectric loss,and easy polarization.It has important application prospects in the field of transverse wave transducers.The intrinsic contribution of the mechanical properties of the[Li?K,Na?]?Nb,Sb,Ta?O₃:Mn?KNNLST:Mn?single crystal of the O phase single domain was investigated.Under the induction of temperature,the single crystal changes phase at around 38°C.By testing the piezoelectric coefficient,dielectric constant,elastic constant and electromechanical coupling coefficient of single crystal with temperature,the phase transition process of electromechanical properties of single crystal was studied.From the perspective of free energy,the free energy path is“flat”,which shows that the electromechanical parameters are rising near the phase transition temperature,while the free energy barrier is growing,and the spontaneous polarization is not easy to deflect,which shows that the parameters have no obvious temperature dependence.Using the coordinate transformation method,the piezoelectric constant and the dielectric constant on the temperature dependence of KNNLST:Mn single crystal are calculated,which provides a basis for studying the intrinsic piezoelectric and dielectric responses of other domain structure single crystals.for example,[001]_C crystallographic orientation is the reason why the single crystal with"4O"domain structure has a high longitudinal piezoelectric constant.The microscopic phase structure and domain structure of the KNNLST:Mn single crystal were investigated using a polarizing microscope and a piezoresponse force microscopy By changing the test temperature,the phase transition of the single crystal at 38?can be observed by PLM and PFM,which is consistent with the macroscopic test results.