Research On Electromechanical Properties Of Sm And Mn Co-Doped Pmnt Piezoelectric Ceramics

Piezoelectric material is a kind of multifunctional dielectric material which can realize the mutual conversion of electrical energy and mechanical energy.It has been widely used in industry,military,medical and other fields.Among all the piezoelectric materials,lead-based perovskite relaxor ferroelectric ceramics Pb(Mg_1/3Nb_2/3)O₃-Pb Ti O₃（PMNT）have the most excellent piezoelectric,dielectric and ferroelectric properties,so they have attracted extensive attention,research and application.Through continuous exploration and research,the comprehensive performance of PMNT ceramics has reached the peak.It is impossible to further improve the comprehensive performance of PMNT ceramics by optimizing the preparation process and looking for the MPB,which seriously limits its application in high-performance piezoelectric devices.At present,it is found that the properties of perovskite ferroelectric ceramics can be further improved by aliovalent doping,so the doping modification in perovskite ferroelectric ceramics has become a research hotspot.In this paper,PMN-30PT ceramics were modified by soft and hard co-doping,and Sm and Mn co-doped PMN-30PT ceramics were prepared.The preparation process,phase structure,microstructure,ferroelectric domain structure,dielectric properties,ferroelectric properties,piezoelectric properties and electromechanical properties were studied.Firstly,the reaction conditions of MgNb₂O₆ precursor,the pre-sintering conditions and sintering conditions of PMN-30PT ceramics with different components were studied.The results show that the reaction conditions of MgNb₂O₆ should be 950 ^oC 150 min,and the pre-sintering conditions of un-doped PMN-30PT ceramics and Mn-doped PMN-30PT ceramics should be 750 ^oC 150 min.Besides,the pre-sintering conditions of Sm-doped PMN-30PT ceramics and Sm and Mn co-doped PMN-30PT ceramics are 850 ^oC 240 min.The sintering conditions of PMN-30PT ceramics with different compositions are 1250 ^oC180min,and the rate of temperature rise and fall is 2 ^oC/min.Then,the phase structure,microstructure and ferroelectric domain structure of the samples before and after doping were studied.It is found that with the increase of Mn doping ratio,the phase structure of the ceramics shifts to the rhombohedral phase,the size of ferroelectric domain increases and the density of ferroelectric domain wall decreases.After Sm doping,the proportion of tetragonal phase increases,the size of ferroelectric domain decreases and the density of ferroelectric domain wall increases.Mn ions can promote the growth of grains,but the average grain size has little change when Sm is doped.Finally,the dielectric,ferroelectric,piezoelectric and electromechanical properties of the samples before and after doping were studied.After doping Mn,the depolarization temperature is observed and hysteresis loop and stress-strain curve of the ceramics are obviously shifted along the E-axis.Besides,the mechanical quality factor of the ceramics increases,the piezoelectric coefficient decreases and the dielectric loss decreases.When Sm is doped,there is no rhombohedral-tetragonal phase transition temperature above room temperature and the value of internal bias field decreases.The d₃₃ of the ceramics increases obviously.In order to explain these phenomena,the multiple effects of local structure heterogeneity and defect dipoles on macroscopic electromechanical properties are proposed.