Performance Optimization And The Study Of Ion Regulation Mechanism Of Barium Titanate-based Lead-free Piezoelectric Ceramics

Piezoelectric ceramics are a type of important advanced functional materials that can interconvert mechanical energy and electrical energy,which have currently served in various fields such as force,light,sound,electricity,and medicine,etc.In the past,lead-based piezoelectric materials have been widely used due to their excellent electrical properties and good temperature stability.However,the main raw material of lead-based ceramics is lead oxide,which is harmful to human health and e co-environment in the process of production and use.Therefore,it is necessary to obtain environmentally friendly lead-free piezoelectric ceramics.As a vital lead-free ferroelectric material,BT piezoelectric ceramics have aroused heated research for many years due to the potential multi-functionality such as piezoelectric,electrostrictive,and electrocaloric properties,etc.In addition to the piezoelectric behaviors,constructing multiphase boundaries near room temperature by doping strategy also accelerates the development of other electro-related properties in BT-based ceramics,such as electrostrictive property and electrocaloric property.Although the dopant modified BT ceramics exhibit the huge potential in the emerging fields of advanced functional devices,to date,there exist few studies on the simultaneous enhancement or balanced development of two or more separate parts of electro-related properties in this type of ceramics.For practical applications,the piezoelectric ceramics would work under severe external conditions with high vibration,high temperature,and pressure.While the effect of chemical modification on the electric performances of BT-based ceramics are well studied,their effects on hardness have received much less attention.Therefore,this paper aims to construct a multiphase coexistence by A-site and B-site doping with barium titanate as the substrate,so as to obtain multifunctional ceramics with a balance of giant piezoelectric properties,excellent electrostriction properties and electrocaloric properties,and to investigate the mechanical behavior（indentation hardness）of BT-based ceramic samples with the best electrical properties,so that the new BT ceramic system designed in this paper has a broader and more diverse practical scope.The main specific research contents are as follows:（1）The Ba_0.9+xSr_0.1-xTi_0.91Sn_0.09O₃（BSr_xTS）ceramic system was prepared by doping Sr²⁺at the A-site of BT ceramics.The phase structure,microstructure,diffuse phase transition behaviors,piezoelectric properties,electrostriction properties and electrocaloric effect of this ceramic system were comprehensively analyzed.To investigate the evolution mechanism of its electrical properties under the action of external field and the intrinsic mechanism of temperature affecting the stability of the properties,to reveal the influence mechanism of microstructure on macroscopic electrical properties,to further elaborate the regulation mechanism of ion doping on electrical properties,to fully optimize its various electrical properties and to significantly broaden the electrocaloric performance span(T_span=49°C,ΔT>0.5K).（2）The Ba_0.9Sr_0.1Ti_1-xSn_xO₃ceramic system（BSTSn_x）was successfully prepared by doping Sn⁴⁺at the B-site in the BT ceramic,detailed analysis of the phase structure,microstructure,domain structure,relaxation behavior and various electrical properties with Sn⁴⁺content,revealing the mechanism of ion doping on the regulation of structure and properties,analyzing the microscopic mechanism of temperature and electric field affecting the stability of ceramic properties,and further optimizing its piezoelectric properties(d₃₃=820p C/N)and electrocal properties（ΔT=0.82 K,ΔE=30 k V/cm）.（3）The mechanical behaviors of BSr_0.1TS and BSTSn_0.08ceramics with excellent electrical properties were characterized and analyzed,respectively.Their load displacement curves under nanoindentation were investigated to probe their indentation size effects and plastic deformation behaviors under different loads,and their hardness behaviors were analyzed based on PSR model and Vickers indentation.