Preparation And Performance Study Of Dy-doped PMN-PT Multifunctional Ceramics With Transparent, Piezoelectric And Luminescent Propertie

The combination of luminescent ions with advanced materials leads to multifunctional optical materials.The potential coupling effects in these materials make them promising for applications in novel displays,multimodal bioimaging,phototherapy,drug delivery,bio-detection,photocatalysis and optical sensing,etc.Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃（PMN-PT for short）relaxed ferroelectric ceramics have excellent piezoelectric properties near the morphotropic phase boundary.The rare earth Dy³⁺has strong emission in the yellow area and are therefore extremely valuable for research in yellow solid-state lasers.Recent studies have shown that Dy³⁺can not only significantly improve the piezoelectric properties of PMN-PT ceramics(PMN-29PT:Dy ceramics,d₃₃^*～1070 pm/V),but also enhance the transparency of PMN-PT ceramics（PMN-25PT:Dy ceramics,transmittance～58%@632 nm）,and also present strong down-conversion photoluminescence.However,the preparation of Dy-doped PMN-PT ceramics with high piezoelectricity,high transmittance,and strong photoluminescence at the same time is still a great challenge due to the harsh preparation conditions,so the potential coupling effects between its various functions remain to be explored in depth.Therefore,in this thesis,PMN-PT:Dy multifunctional ceramics were prepared by a two-step sintering method,making them one of the transparent multifunctional ceramic alternatives for high piezoelectricity and strong photoluminescence.The effects of different PMN/PT solid solution ratios on the microstructure,optical properties,and electrical properties of PMN-y PT-3Dy ferroelectric ceramics were investigated;the effects of different Dy doping amounts on the microstructure,photoluminescence,and electrical properties of PMN-31PT-xDy transparent multifunctional ceramics were studied;the effects of different Dy doping amounts on the electrical properties,domain structure and domain switching（field induced strain and ferroelectric dynamic hysteresis scaling behavior）of PMN-28PT-xDy ceramics with high piezoelectric coefficient d₃₃were investigated.The main results of this paper are as follows:1.Ferroelectric ceramics with different solid solution ratios of PMN-y PT-3Dy（y=25,26.5,28,29.5 and 31%）were prepared.The effects of different PMN/PT solid solution ratios on the microstructure,optical properties,and electrical properties were investigated.The results show that all samples are pure perovskite structures;the y=31%ceramics have the highest transmittance,with 42%at 900 nm;and the y=28%ceramics have the highest piezoelectric properties with a piezoelectric coefficient d₃₃of 1270 pC/N and an electromechanical coupling coefficient k_pof 0.71.2.PMN-31PT-xDy（x=0,1,2,3 and 4%）transparent multifunctional ceramics with different Dy doping amounts were prepared.The effects of Dy doping amount on their microstructure,photoluminescence and electrical properties were investigated.The results show that the linear transmittance is enhanced at x=3%,reaching a maximum value of42%（@900 nm）,producing stronger yellow light emission at a wavelength of 573 nm under 454 nm excitation,obtaining an extreme value of the piezoelectric coefficient d₃₃～940 pC/N,and also obtaining a maximum value of the room temperature dielectric constantε_r～7080（@1 kHz）,T_m=130℃.The above results show that Dy doping has a great influence on the transmittance,photoluminescence and piezoelectric properties of the ceramics,and proper Dy doping makes PMN-31PT:Dy transparent ceramics an alternative for multifunctional materials.3.PMN-28PT-xDy（x=0,1,2,3 and 4%）piezoelectric ceramics with high piezoelectric coefficient d₃₃were prepared and their domain structure and domain switching mechanism were investigated.The results show that the extreme values of the piezoelectric coefficient d₃₃～1270 pC/N were obtained for x=3%;the maximum value of the room temperature dielectric constantε_r～7565（@1 kHz）was obtained with T_m=97℃.With increasing Dy doping content,the domain structure changes from ordered stripe domains to disordered watermarks domains,while the average domain size decreases significantly from～635 nm to～100 nm.Domain switching is investigated by strain curves and calculating the corresponding ferroelectric dynamic hysteresis scaling behavior from hysteresis loops measured at different electric field amplitudes and frequencies.It is found that for complete polarization of PMN-28PT-xDy ceramics,the electric field amplitude should preferably be higher than 2.5E_c.If the ceramics are polarized under an electric field of 3E_c,the electric field frequency should preferably not exceed f₂.The above results show that the rare-earth Dy doping has a significant effect on the domain structure and domain switching as well as the piezoelectric properties.