Preparation And Properties Of Ce And Tm Element Doped Modified PMN-PT Transparent Ferroelectric Ceramic

The relaxed ferroelectric lead niobate-lead titanate(（1-x）Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃,PMN-xPT)has ultra-high piezoelectric properties and has been successfully applied to medical ultrasound imaging,ultrasound motors,microelectromechanical systems（MEMS）and other fields.It is found that transparent PMN-xPT ferroelectric single crystals/ceramics can be prepared by AC polarization or rare earth element doping to realize multifunctional coupling of acousto-optical-electricity,which is expected to be applied in medical photoacoustic imaging,electro-optical information modulation,transparent piezoelectric sensing/actuation.However,the scattering of light by domain walls,grain boundaries and pores in ferroelectric ceramics makes the preparation of highly transparent ferroelectric ceramics very difficult,which is a major problem that needs to be solved at present.Based on the experience of our group in preparing La（lanthanum）and Sm（samarium）doped PMN-xPT transparent ceramics,this paper investigates the preparation process,phase structure,microstructure,ferroelectric,piezoelectric,dielectric and electro-optical properties of Ce（cerium）and Tm（thulium）doped PMN-xPT transparent ceramics,summarizes the laws of doping modulation of rare earth elements,and systematically analyzes the doping modification mechanism,the main results obtained are as follows.1.translucent Ce doped PMN-0.33PT ferroelectric ceramics were prepared by a two-step sintering method,and the effect of Ce doping concentration on the structure and properties of the ceramics was investigated.XRD results showed that the ceramic samples had a pure perovskite phase structure and were located near the morphotropic phase boundary（MPB）.the SEM results showed that the ceramics were highly dense and dominated by crystal penetration fracture.With the increase of Ce doping,the ferroelectricity of the ceramics decreases,the Curie temperature decreases,the relaxation characteristics are enhanced,and the piezoelectric coefficient d₃₃ reaches the optimum at 2mol%doping（800 p C/N）.The results of the down-conversion luminescence tests indicate that the luminescence under UV excitation mainly originates from the luminescence of Pb ions in the matrix itself.Combined with the shift of XRD peak and the change of Curie temperature T_m,the valence state of Ce ions and the solid solution occupation distribution were analyzed by XPS test.2.The structure and properties of PMN-xPT（x=0.37,0.35,0.33,0.31,0.29）ceramics with different solid solution ratios at 2.5 mol%Ce doping concentration were investigated.XRD results showed that a small amount of pyrochlore phase appeared in most samples,SEM observation revealed a small amount of porosity in some ceramics,and EDS indicated that the distribution of elements in the solid solution was relatively uniform.The piezoelectric coefficient and electromechanical coupling coefficient show the law of increasing and then decreasing with the increase of solid solution ratio.When the solid solution ratio x=0.31,the PMN-PT ceramics have the optimal piezoelectric constant (d₃₃=837 p C/N),dielectric coupling coefficient（K_p=0.65）dielectric（ε_r=29466）properties.3,Tm-doped PMN-0.12PT transparent electro-optical ceramics were prepared and the effects of doping concentration on the phase composition,microstructure and electrical,optical and electro-optical properties of the ceramics were investigated.the maximum transmittance of PMN-PT transparent ceramics is about 70%,which is close to its theoretical limit transmittance of 71%.The minimum half-wave voltage V_πand the maximum electro-optical coefficient r_c are 355 V and 33.97×10^-16m²/V²,respectively,measured by the single-beam compensation method,and the half-wave voltage is much lower than that of common electro-optical materials such as Li Nb O3 and PLZT,and the electro-optical coefficient is second only to those reported by the Shanghai Institute of Ceramics,Chinese Academy of Sciences and ourselves.The low half-wave voltage and large electro-optical coefficient indicate that this transparent ceramic has a good application prospect in electro-optical modulation.