Effect Of Ion Doping On The Electrical Properties Of CaBi₄Ti₄O₁₅Bismuth Layered High-curie-temperature Piezoelectric Ceramics

Bismuth layered piezoelectric ceramics have attracted extensive attention and research because of their characteristics of non-toxic and high Curie temperature.In addition,bismuth layered piezoelectric ceramics have the advantages of low sintering temperature,good fatigue resistance,low aging rate,low dielectric loss,high breakdown strength and good temperature stability.However,due to the spontaneous polarization of bismuth layered structure is limited to the a-b two-dimensional plane,and the high coercive field strength makes it difficult to polarize sufficiently,which leads to poor piezoelectric activity and very low piezoelectric constant(d₃₃),thus limiting its application.In order to solve these problems,researchers usually adopt the method of ion doping to modify it.Ca Bi₄Ti₄O₁₅（CBT）is a BLSF material with m=4.In the perovskite-like layer(Ca Bi₂Ti₄O₁₃)^2-,the A-site is occupied by Ca²⁺and Bi³⁺mixed ions,while the B-site is occupied by Ti⁴⁺.The piezoelectric constant d₃₃of the undoped sample is 8.0 p C/N,and the Curie temperature is 790℃.In this paper,the ion doping method is used to modify CBT in order to improve its comprehensive performance and expand its application.Firstly,Ca_1-xCe_xBi₄Ti₄O₁₅（CCBT,x=0.00,0.02,0.04,0.06,0.08,0.10）bismuth layered structured piezoelectric ceramics were prepared by using the solid-state reaction method.The effect of A-site Ce doping on crystal structure,microstructure,dielectric and piezoelectric properties of the ceramics was investigated.All samples had bismuth layered structure with m=4 and Bi₂Ti₂O₇pyrochlore was present as the second phase when x≥0.08.The concentration of the oxygen vacancy was reduced by Ce doping,which reducing the dielectric loss,and effectively improving the polarization performance,and lift the piezoelectric constant coefficient.Significantly enhanced piezoelectric coefficient(d₃₃=17p C/N)was achieved for the ceramic sample with x=0.06,over two times than that of CBT(d₃₃=8 p C/N).Meanwhile,this ceramic also had high Curie temperature（T_c=773℃）,low dielectric loss at room temperature（tanδ=0.7%）and high resistivity(ρ_dc=6.4×10~7Ω·cm@500℃).Furthermore,after annealing at 550℃,d₃₃still retained to be 14.2 p C/N,more than 80%of the room temperature value.Secondly,based on the best composition of Ce doping CBT,Ca_0.94Ce_0.06Bi₄Ti_4-xNb_xO₁₅（CCBTN,x=0.02,0.04,0.06,0.08,0.10,0.12）bismuth layered structured piezoelectric ceramics were prepared by using the solid-state reaction method.The effects of B-site Nb⁵⁺doping on the crystal structure,microstructure,dielectric and piezoelectric properties of CCBT ceramics were investigated.The results of X-ray diffraction show that all the samples had a single bismuth layered structure phase with m=4.By Nb⁵⁺doping in B-site,the grain size of ceramic was significantly reduced,and its comprehensive electrical performance were improved effectively.When x=0.06,the ceramic had the best piezoelectric coefficient(d₃₃=19.2 p C/N).When annealing to 500℃,it retained more than90%of the room temperature value,indicating its good thermal stability.Meanwhile,it maintains a high Curie temperature（T_c=769℃）,high resistivity(ρ_dc=2.0×10~7Ω·cm@500℃).Especially,compared with the CCBT ceramic（tanδ=0.50@500℃）,the dielectric loss significantly reduced（tanδ=0.08@500℃）.Finally,based on the best composition of Ce doping CBT,Ca_0.94Ce_0.06Bi₄Ti_4-xW_xO₁₅（CCBTW,x=0.02,0.04,0.06,0.08,0.10,0.12）bismuth layered structured piezoelectric ceramics were prepared by using the solid-state reaction method.The effects of B-site W⁶⁺doping on the crystal structure,microstructure,dielectric and piezoelectric properties of CCBT ceramics were investigated.The results of X-ray diffraction show that all the samples had a single bismuth layered structure phase with m=4.When the W⁶⁺-doping amount is little,the electrical performance of CCBT ceramics were improving with the benefits of improvement in piezoelectric coefficient and resistivity,reducement in the activation energy and dielectric loss within specific temperature range.When x=0.04,the ceramics have the highest piezoelectric coefficient(d₃₃=20.2 p C/N).Meanwhile,it also has high Curie temperature（T_c=753℃）,low dielectric loss at room temperature（tanδ=0.68%）and high resistivity(ρ_dc=1.10×10~7Ω·cm@500℃).The comprehensive excellent performance of A/B-site co-doping CBT ceramics has a good application value in the field of high temperature piezoelectric sensor production.