Preparation And Performance Study Of Element-doped Modified PMN-PT Piezoelectric Ceramics And Transparent Electro-optic Ceramics

Relaxor ferroelectric lead magnesium niobate-lead titanate[molecular formula?1-x?Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃,abbreviated as PMN-xPT]has excellent piezoelectric,electro-optic,pyroelectric performance,which has become the primary materials of high-end devices in the fields of medical ultrasound imaging,industrial nondestructive testing,underwater sonar,electro-optic modulation,infrared imaging and other fields.In 1997,the discovery of the PMN-xPT single crystals were evaluated by Science as"Improvements by a factor of 10 are not easy to come by in a field that's 50 years old and considered mature."From 2018 to 2020,Science,Nature,and Nature Materials journals reported that the rare earth element doping has greatly improved PMN-xPT single crystal/ceramic's piezoelectric coefficient,electromechanical coupling coefficient,light transmittance and other properties further enhance the application prospect of the materials.Element doping modification of PMN-PT-based materials and its high-performance generation mechanism have become new research hotspots.In this thesis,element-doped PMN-xPT powder was prepared by the niobite method,and PMN-xPT ceramics were prepared by a two-step sintering method.The effects of element doping type,element doping concentration,PMN-xPT solid solution ratio,ceramic preparation process and other factors on the structure and properties of PMN-xPT ceramics were studied.PMN-PT piezoelectric ceramics with high piezoelectric coefficient,high mechanical quality factor,and high electromechanical coupling coefficient were successfully prepared,and PMN-xPT transparent ceramics with high electro-optic performance also were prepared.The details are as follows:1.The effect of Mn doping amount on the structure and properties of PMN-0.25PT ceramics was studied:it was found that 3 mol%Mn doping can greatly improve the mechanical quality of ceramics on the premise of slightly reducing the piezoelectric coefficient d₃₃ and the electromechanical coupling coefficient k The factor Q_m,?up to about 15 times?,greatly improves the overall quality factor FOM?Q_m?d or Q_m?k²?of the materials,and enhances its application prospects in high-power devices.It was found that the aged 3 mol%Mn-doped PMN-0.25PT ceramics exhibited double hysteresis loops,and after polarization,there were obvious asymmetric field-induced strain with strain memory phenomena and the application of"defect symmetry consistency"explanation.2.The effect of Sm doping on the structure and properties of PMN-xPT ceramics with different solid solution ratios was studied:it was found that Sm doping can greatly improve the piezoelectric properties of ceramics.The piezoelectric coefficient d₃₃ of2.5mol%Sm-doped PMN-xPT ceramic reached 1634 pC/N,and the electromechanical coupling coefficient k_p reached 80.66%,both higher than the performance reported by Nature Materials in 2018 and the known highest value at present.The phase transition and microstructure of PMN-PT ceramics with different piezoelectric properties were studied by means of dielectric temperature spectra before and after polarization,selected area electron diffraction of transmission electron microscopy,bright and dark field images and high-resolution images.The high-density heterogeneous polar region explains the mechanism of its high piezoelectrical properties.3.Sm-doped PMN-xPT transparent electro-optic ceramics with near-infrared band materials with transparency close to 55%were prepared.The relationship between light intensity and voltage was measured using the improved single-beam compensation method.The electro-optic coefficient of the ceramic is about 1073 pm/V,which is about 50 times that of the lithium niobate single crystal,which is much higher than the electro-optic coefficient of the PMN-PT single crystal and other electro-optic materials currently reported;the half-wave voltage is about 100V?sample thickness 0.8mm,width 1mm?,far lower than the half-wave voltage of KDP single crystal and LiNbO₃single crystal;indicating that Sm-doped PMN-PT transparent electro-optic ceramics have good application prospects in the field of optical communication.