Preparation Of Bismuth Calcium Titanate Based High Temperature Piezoelectric Ceramics Based On Co-regulation Of Complex Ions And Study On Piezoelectric Enhancement Mechanism

Piezoelectric material is an important functional material in the field of industrial production.It can be used in the manufacture of accelerators,transducers,resonators and sensors.In recent years,with the increasing demand for piezoelectric materials in modern industry,the application requirements have become increasingly harsh.It has gradually developed into a more severe high temperature and high frequency environment from the initial normal temperature and low frequency environment.It is difficult for traditional PZT materials to cope with such extreme environment.Therefore,the ability of piezoelectric materials to withstand high temperature and high frequency has been improved.In addition,the sensitivity requirements of piezoelectric materials have also improved.Combining these requirements,the development of a new type of high-temperature piezoelectric ceramics has become an urgent and important task.Bismuth layered ferroelectric ceramics is an important member of the piezoelectric ceramic.It was first discovered by Aurivillius et al.Bismuth layered ferroelectric structure（BLSFs）consists of two-dimensional pseudo-perovskite layers and（Bi₂O₂）²⁺layers.Bismuth layer structure has one more（Bi₂O₂）²⁺layer than the perovskite structure.It has high Curie temperature and strong ferroelectricity due to its own structure characteristics.Ca Bi₄Ti₄O₁₅（CBT）piezoelectric ceramic is a member of bismuth layered piezoelectric ceramics,and it has received widespread attention due to their high phase transition temperature of 790 ^oC.However,it is also restricted by the characteristics of structure,the spontaneous polarization is limited in two-dimensional plane,so the piezoelectric coefficient is very low.Secondly,due to the high content of bismuth,it is easy to cause bismuth to volatilize during the high-temperature sintering process,thereby generating oxygen vacancies,making the resistivity of the ceramic very low,affecting its sensitivity in high-temperature environments.Combining these two factors,this article uses Ti-site complex ions to synergistically control the crystal lattice structure and oxygen vacancy concentration of ceramics.Thus piezoelectric properties and other electrical properties of piezoelectric ceramics can be improved and optimized.In this paper,a traditional solid-phase reaction sintering method was used to synthesize modified CBT-based piezoelectric ceramics coordinated by composite ions.We compared the effects of different high-valent cation ion radius,electronegativity and electronic configuration on the electrical properties of CBT-based ceramics.The physical mechanism of piezoelectric activity is analyzed,and the physical law and other electrical properties of piezoelectric activity are mastered.The piezoelectric coefficient of high-temperature piezoelectric ceramics is higher than 22 p C/N,Curie temperature is higher than 790 ^oC and the resistivity is higher than 10⁸Ω·cm at 400^oC,together with good thermal stability.1.In this paper,modified CBT-based piezoelectric ceramics coordinated by Ti-site Ta/Mn,Sb/Mn,and Nb/Mn composite ions were prepared.The effects of doping concentration and different high-valent cations on the microstructure,dielectric properties,piezoelectric properties and thermal stability of ceramics were discussed.The results show that high cation combined with Mn²⁺can remarkably improve the activity and resistivity of CBT-based piezoelectric ceramic.The piezoelectric coefficient of CBT ceramics co-doped with Sb/Mn was increased to 25p C/N.This is a very high level in the current reported study,with a 2.5-fold increase compared to the pure sample.The improvement of piezoelectric performance is greatly related to the optimization of lattice structure and the reduction of oxygen vacancy concentration.And the resistivity has been improved by dozens of times.Especially,after the Ta/Mn co-doping,resistivity increases from 1.47×10⁷Ω·cm to4.96×10⁸Ω·cm,achieving a 30-fold increase and exhibiting extremely high resistivity.In terms of dielectric properties,the Curie temperature of each experiment keeps above 790 ^oC,which did not have a great impact on it.And the piezoelectric coefficient keeps above 85%of the initial value after annealing at 600 ^oC for two hours,which is closely related to the reduction of defects and unstable non-180 o domain.2.Based on the above idea,we used higher valence W/Cr and Mo/Cr coordinated regulation to replace Ti⁴⁺and prepared Ca Bi₄Ti_4-x(B_1/2Cr_1/2)_xO₁₅ modified ceramics,where B is W or Mo.The piezoelectric activity was increased again,the oxygen vacancy concentration was reduced again,and the other electrical properties still maintain at a high level.The results show that the piezoelectric activity can be greatly improved by the higher ion（Mo/Cr）substitution.The piezoelectric coefficient of the modified ceramic controlled by Mo/Cr is increased to 25 p C/N,but the resistivity is only increased by 7 to 8 times than pure CBT ceramic,which is not as good as that of the Mn experiment.After annealing at 600°C for two hours,the piezoelectric coefficient of the two groups of experiments can still maintain more than 90%of the initial value.About dielectric properties,the Curie temperature is still maintained at about 790 ^oC.These results prove that CBT modified ceramics coordinated by complex ions have great application potential in the field of high-temperature piezoelectricity.