| Piezoelectric ceramics are greatly vital functional materials,which play a role in numberous fields,such as sensors,aerospace,automotive and so on.With the prosperity of modern science and technology,the application ranges of piezoelectric ceramics are more extensive,so the high temperature requirements of its application are in such a huge demand.High-power ultrasonic transducers,high-temperature detectors in nuclear reactors,high-temperature probes in explorations,advanced automotive systems,fuel injectors and other core devices,all must use piezoelectric ceramic materials with high Curie temperature.However,the traditional piezoelectric ceramics are Pb(Zr,Ti)O3,which we abbreviate it as PZT piezoelectric ceramics.The Curie temperature of PZT materials is low,which greatly limits its use in special environments.Therefore,researchers have been exploring piezoelectric materials with high Curie temperature and excellent properties.At present,most high-temperature piezoelectric devices use expensive piezoelectric single crystal materials,such as LiNbO3,GaPO4,AIN,etc.But these single crystal materials have complex production process,high manufacturing cost and relatively weak piezoelectric activity.Consequently,it is very urgent and necessary to investigate high temperature piezoelectric ceramics with excellent properties.Up till now,the high-temperature piezoelectric ceramics are mainly divided into perovskite type,tungsten bronze structure and bismuth layered structure piezoelectric ceramics.Bismuth-layered structure piezoelectric ceramics have the advantages of low dielectric loss,low aging rate,high Curie temperature,high resistivity,easy sintering and low cost.Hence,bismuth-layered structure piezoelectric ceramics have good research and application prospects in the fields of high temperature and high frequency.Bi3TiTaO9 based piezoelectric ceramics studied in this thesis is a kind of bismuth-layered structure piezoelectric ceramics.It has a high Curie temperature of 871℃.But its piezoelectric coefficient is low(d33 is only 4 pC/N).In order to get high application values of Bi3TiTaO9,it is necessary to improve its piezoelectric coefficient on the premise of little change in Curie temperature.Improving the piezoelectric properties of materials generally require improving the preparation process or doping modification.Because the cost of improving the preparation process is higher,the operation is complex and the manufacturing time cycle is long,this thesis adopts the experimental method of doping modification to improve the performance of materials.In this thesis,making Bi3TiTaO9 as the matrix,the effects of ion doping at A and B sites on the microstructure,dielectric properties,piezoelectric properties and ferroelectric properties of Bi3TiTaO9 ceramics were systematically studied.(1)Bi3-xLaxTiTaO9(x=0.00～0.20)and Bi3-xCexTiTaO9(x=0.00～0.06),were prepared by doping La and Ce at A-site.The effects of La and Ce on the microstructure and electrical properties of ceramics were studied respectively.When La doping content x=0.10,the piezoelectric coefficient can be increased to 11.2 pC/N,the Curie temperature is 821℃,and the dielectric loss is only 0.16%.And when Ce doping content x=0.04,the piezoelectric coefficient can be increased to 14.9 pC/N,the Curie temperature is 851℃,and the dielectric loss is only 0.29%;(2)Bi3Ti1-xCrxTaO9(x=0.00～0.06),Bi3Ti1-xWxTaO9(x=0.00～0.06),Bi3Ti1-xMoxTaO9(x=0.00～0.06)were prepared by doping Cr,W and Mo at B-site.The effects of Cr,W and Mo on the interior structure,dielectric properties,piezoelectric properties and ferroelectric properties of ceramics were studied respectively.When Cr doping content x=0.02,the piezoelectric coefficient can be increased to 16.3 pC/N,the Curie temperature can be increased to 882℃,the dielectric loss is only 0.21%,and the resistivity can reach 5.09×105Ω·cm at 500℃.When W doping content x=0.03,the piezoelectric coefficient can be increased to 13.7 pC/N,the Curie temperature can be increased to 883℃,the dielectric loss is only 0.51%,and the resistivity can reach 3.66×107Ω·cm at 500℃.And when Mo doping content x=0.03,the piezoelectric coefficient can be increased to 11.0 pC/N,the Curie temperature can be increased to 893℃,the dielectric loss is only 0.50%,and the resistivity can reach 2.45×107Ω·cm at 500 ℃.(3)Bi3Ti1-x(Cr2/3W1/3)xTaO9(x=0.00～0.10)、Bi3Ti1-x(Cr2/3Mo1/3)xTaO9(x=0.00～0.08)were prepared by co-doped of B-site mixed valence ions(W/Cr and Mo/Cr).B-site mixed valence doping can achieve the effect of B-site single doping and obtain higher resistivity.When W/Cr doping content x=0.06,the piezoelectric coefficient can be increased to 17.5 pC/N,the Curie temperature is 874℃,the dielectric loss is only 0.17%,and the resistivity is 5.13×106Ω·cm at 500℃.And when the doping content of Mo/Cr is x=0.04,the piezoelectric coefficient can be increased to 17.4 pC/N,the Curie temperature is 876℃,the dielectric loss is only 0.46%,and the resistivity is 3.31×106Ω·cm at 500℃. |
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