Structure,Electrical And Luminescent Properties Of Rare Earth-doped K_0.5Na_0.5NbO₃ And CaBi₂Nb₂O₉-based Lead-free Piezoelectric Ceramics

In recent years,rare earth-doped piezoelectric ceramics have attracted much attention due to their simultaneous existence of ferroelectric,piezoelectric and luminescent properties.Rare earth ions with high valence,as donor dopants,can be introduced into piezoelectric ceramics to improve the electrical properties of the materials;meanwhile,rare earth ions possess abundant energy levels and can induce the fluorescence in the rare earth-doped piezoelectric ceramics.Among piezoelectric ceramics,perovskite alkali potassium-sodium niobate K_0.5Na_0.5NbO₃?KNN?and bismuth layer structure CaBi₂Nb₂O₉ ceramics have been widely studied because of their excellent electrical properties,high Curie temperature and excellent luminescence by introducing rare earth ions into their crystal lattices.In this thesis,rare earth ions(Dy³⁺,Er³⁺/Yb³⁺)-doped K_0.5Na_0.5NbO₃ ceramics and complex ions(Li_0.5Er_0.5)²⁺-doped CaBi₂Nb₂O₉ lead-free ceramics were prepared by an ordinary solid state method and their structure,electrical and luminescent properties were investigated in detail.The main results are listed as follows:?1?(K_0.48Na_{0.480Li0.041-x} Dy_x/3(Nb_0.90Ta_0.04Sb_0.06)O₃ lead-free multifunctional ceramics were successfully prepared by the conventional solid state method and the phase structure,microstructure,electrical and luminescent properties of the ceramics were systematically studied.With the x increasing from 0 to 0.03,the Pr decreases from 27.0to 1.3 ?C/cm² and the d33 decreases from 198 to 52 p C/N.Under the excitation of 453 nm,two emission peaks centers 476 nm and 573 nm of Dy³⁺are observed in the materials,corresponding to the 4F9/2 ? ⁶H_15/2 and ⁴F₍9/2( ? ⁶H_13/2,respectively.The strongest fluorescence-emission is observed in the material with x = 0.015.?2?0.96(K_0.47Na_0.47Li_0.06)(Nb_0.94Sb_0.06)O_3-0.04SrTiO₃:Er/xYb lead-free piezoelectric ceramics were prepared by a traditional solid state reaction technique and the phase structure,microstructure,electrical and luminescent properties of the ceramics were studied in detail.The optimal piezoelectric?d33 = 98 p C/N?and ferroelectric properties?Pr = 9.4 ?C/cm²?are obtained in the ceramic with x = 0.02.Under the excitation of 980 nm,three emission peaks centers of Er³⁺ions are observed at 534 nm,554 nm and 672 nm,corresponding to the ²H_11/2?⁴I_15/2,⁴S_3/2 ?⁴I_15/2 and ⁴F_9/2 ?⁴I_15/2,respectively.For the ceramic with x = 0.02,the temperature dependence of the luminescence shows that the fluorescence-emission intensity of the material is highly sensitive to temperature.?3?Ca_1-x(Er_0.5Li_0.5)_x Bi₂Nb₂O₉ lead-free piezoelectric ceramics have been prepared by a traditional solid state reaction technique and the effects of Er³⁺/Li⁺ co-doping on the phase structure,microstructure,electrical and luminescent properties of the ceramics have been investigated.The ceramic with x = 0.08 exhibits the optimum piezoelectric constant d33 of 12.1 p C/N.Under the excitation of 980 nm,three emission peak centers of Er³⁺are observed at 534 nm,554 nm and 672 nm,respectively,corresponding to the ²H_11/2 ? ⁴I_15/2,⁴S_3/2? ⁴I_15/2 and ⁴F_9/2 ? 4I_15/2.The strongest fluorescence-emission is observed at x = 0.08.Interestingly,rare near-infrared Er³⁺emission of ⁴S_3/2 ? ⁴I_13/2,⁴F_9/2?⁴I_13/2 and ⁴S_3/2 ?⁴I_11/2 are observed in the Er³⁺/Li⁺-codoped CaBi₂Nb₂O₉ ceramics.