Study On Structure Optimization And Optical、Electrical Properties Of The BT-Based Ceramics

In many lead-free piezoelectric ceramic systems,Barium Titanate（Ba TiO₃,BT）-based lead-free piezoelectric ceramics is undoubtedly one of the most concerned system,due to their good piezoelectric properties.However,BT-based ceramics have poor temperature stability in current studies,which can not be widely used.In this paper,two ways are used to enhance the properties of the BT-based piezoelectric ceramics.First,isovalent ions are doped in BT-based ceramics for researching the better piezoelectric properties and temperature stability.Second,the rare earth elements（RE）of different valent are introduced in BT-based ceramics for exhibiting good piezoelectric properties and photoluminescence properties simultaneously.The details are listed below:1.The Ca²⁺,Hf⁴⁺ions are introduced to replace the isovalent Ba²⁺,Ti⁴⁺ions and the(Ba_1-xCa_x)(Ti_0.95Hf_0.05)O₃（x=0.04-0.14,BCHT）ceramics are prepared.Researches on phase structures,surface morphologies and electrical properties have been conducted for the BC HT ceramics.Results show that all BCHT ceramics exhibit a single perovskite structure.The appropriate ionic doping may shift the tetragonal-orthorhombic phase transition temperature(T_O-T)to room temperature（RT）,while not affect the tetragonal-cubic phase transition temperature（C urie temperature,T_C）.When x=0.08,the BCHT（BC HT-0.08）ceramics exhibit the best electrical properties:piezoelectric coefficient d₃₃=380 pC/N,remanent polarization P_r=13.4μC/cm² and mechanical coupling coefficient k_p=50%.The temperature stability and polarization treatment of the BCHT ceramics are studied.The temperature aging rate of d₃₃ values at 90°C is not more than 20%,indicating that the BCHT ceramics have good temperature stability.For the poled BC HT-0.08 ceramics,the phase coexistence region of tetragonal（T）and orthorhombic（O）phases becomes narrow,and more tetragonality is exhited.In addition,the dielectric loss tanδdecreases obviously for the poled BCHT-0.08 ceramics.2.Theelectricalandluminescencepropertiesofthe(Ba_0.99Ca_0.01)(Ti_0.98Zr_0.02)O₃-Pr₆O₁₁（BCZT-Pr）and(Ba_0.99Ca_0.01)_1-xEu_x(Ti_0.98Zr_0.02)O₃（x=0-0.006,BCZT-Eu）ceramics are studied.Results show that the T_O-T of ceramics are shifted to RT by doping the RE ions,and the piezoelectric properties of ceramics are improved(BCZT-Pr d₃₃=344 pC/N,BCZT-Eu d₃₃=400 pC/N).Desired luminescence properties（bright reddish-orange light,emission peak centered at 649 nm）are obtained under an excitation of 448 nm blue light at RT for the BCZT-Pr ceramics.Upon the excitation of465 nm blue light,the BC ZT-Eu ceramics have intense emission peak centered 616 nm which is corresponding to bright yel ow light.3.The effect of the Sm³⁺ions doped into(Ba_0.95Ca_0.05)(Ti_0.90Sn_0.10)O₃（BCST）ceramics are researched in this paper.Results show that:compared with the BCST ceramics,(Ba_0.95Ca_0.05)(Ti_0.90Sn_0.10)O₃-0.002Sm₂O₃（BCST-Sm）ceramics exhibit good comprehensive electrical properties:d₃₃=450 pC/N and k_p=52%.The BCST-Sm ceramics show a strong photoluminescence with a reddish-orange emission centered at596 nm excited by 409 nm blue light.In addition,the electrical and luminescence properties of the BCST-Sm ceramics are studied after polarization treatment.Polarization treatment induces obvious structural changes for the BCST-Sm ceramics,and brings significant changes of electrical properties and luminescent intensity.With the increase of the electric field,the tetragonality of the BCST-Sm ceramics improves gradually.The poled BCST-Sm ceramics exhibit optimal piezoelectric property(d₃₃=450 pC/N)under the applied field of 20 k V/cm.Furthermore,the polarization-induced photoluminescence quenching is observed obviously.The intensity of the PLE peaks for the BCST-Sm ceramics decreases drastically and a minimum value of the PLE peaks is achieved at 20kV/cm.