Ferroelectric,Piezoelectric And Photoluminescence Properties Of Perovskite Structure Piezoelectric Ceramics

Piezoelectric ceramics,as a functional material that can convert electrical energy and mechanical energy,play an indispensable role in electronic devices such as sensors,actuators,ultrasonic transducers and et al.Today,in the application fields of piezoelectric materials,those excellent lead piezoelectric materials,like PZT and PMN-PT,still dominate.However,as the demand of a better environment increasing,the limit on the use of lead-containing materials will be increasingly strict.So it is urgent to find a lead-free piezoelectric material that is comparable in performance to lead piezoelectric materials to replace lead materials.In the past 20 years,research on lead-free piezoelectric ceramics has reached a lot of achievements.By doping,BaTiO₃?BT?-based and?K,Na?NbO₃?KNN?-based ceramics with piezoelectric coefficients above500 pC/N can be prepared by conventional solid-state reaction.They have been comparable with some lead-containing piezoelectric materials in piezoelectric coefficient.It also further strengthened the confidence of people to replace lead piezoelectric materials with lead-free piezoelectric ceramics.Rare earth elements have important applications in the production of fluorescent materials,electric light source materials,laser materials,superconducting materials and many other materials,and are an important natural resource.Li et al.obtained PMN-PT ceramic with a piezoelectric coefficient of up to 1500 pC/N and a Curie temperature of 89°C by incorporating 2.5%Sm³⁺.Compared with undoped PMN-PT of which the piezoelectric coefficient is less than 1000 pC/N,the dielectric property has been greatly improved.This result indicates that the doping of rare earth elements has great potential in improving the performance of piezoelectric materials.At present,the work on rare earth doped lead-free piezoelectric ceramics has rarely been reported.Can KNN and BCTZ,which are of the perovskite structure just like PMN-PT,also improve their piezoelectric properties through the incorporation of rare earth elements?This question is completely worth exploring and verifying.China has abundant rare earth mineral resources,excellent ore-forming conditions,and reserves also take the first prize in the world.The application of rare earth elements in the piezoelectric field can make China's utilization of rare earth elements a new step.Based on the above thinking,we mainly do the following two parts of research:?1?Solid-state reaction method was used to prepare?1-x??Li,Sb?KNN-xBKZ,0.965?Li,Sb?KNN-0.035BKZ:yEr and 0.965?Li,Sb?KNN-xBKZ:0.25%Er/z In three ceramics,where x=0⁵%,y=0¹.75%,z=0¹%,?Li,Sb?KNN and BKZ stand for K_0.40Na_0.58Li_0.02Nb_0.96Sb_0.04O₃ and Bi_0.5K_0.5ZrO₃ respectively.The effects of Bi_0.5K_0.5ZrO₃?abbreviated as BKZ?,Er³⁺and In³⁺on the ferroelectric and piezoelectric properties of KNN-based ceramics were investigated.The XRD patterns of the obtained samples showed that all the ceramics were perovskite structures,and no second phase existed,which indicates that BKZ,Er³⁺and In³⁺can form a continuous solid solution with the KNN matrix in the doping range above.When the doping amount of BKZ is x=3.5%,the piezoelectric coefficient of ceramic reaches the maximum(d₃₃³12 pC/N),then d₃₃ begins to decrease with the increase of x;the incorporation of Er³⁺causes the piezoelectric coefficient of ceramic to decrease rapidly.A small amount of In³⁺can increase the piezoelectric coefficient of ceramics.When the In³⁺doping amount z is0.25%,the piezoelectric coefficient of ceramic is 253 pC/N,which is the maximum piezoelectric coefficient reported in the rare earth doped KNN system.The upconversion luminescence intensity of 0.25%Er³⁺/zIn³⁺co-doped KNN ceramics is closely related to the content of In³⁺:with the incorporation of a small amount of In³⁺,the green emission light intensity at 525 nm and 550 nm is gradually enhanced and reaches its maximum at z=0.5%.The intensity finally decreases,which is due to the quenching caused by excess In³⁺doping.Through the analysis of the absorption spectrum of ceramic samples,we found that In³⁺can increase the content of isolated Er³⁺and modify the distribution of Er³⁺in the matrix.?2?Eu³⁺doped 0.5Ba?Ti0.8Zr0.2?O3-0.5?Ba0.7Ca0.3?TiO3?abbreviated as BCTZ?ceramics was prepared by solid state reaction method,and then its surface morphology and phase structure,ferroelectric,piezoelectric and luminescent properties were characterized to explore the effect of Eu³⁺-incorporation on BCTZ performance.Eu³⁺is well compatible with BCTZ when the doping amount is less than 1.25%,and a heterophase is formed in BCTZ after the doping amount is greater than 1.25%.The incorporation of Eu³⁺causes the decrease of Curie temperature and the minification of grain size for the BCTZ ceramics,which in turn leads to a decrease in ferroelectric properties and piezoelectric coefficient.The BCTZ doped with Eu³⁺can obtain a complete emission spectrum under the illumination of 395 nm excitation light.When the Eu³⁺content is x?1.5%,the intensity of the emitted light at 613 nm increases with increasing x.When x>1.5%,the intensity of the emitted light decreases rapidly,which is caused by quenching.The addition of a small amount of rare earth ions to the perovskite piezoelectric ceramics imparts its photoluminescence properties while maintaining its own piezoelectric properties,making it a multifunctional material and greatly expanding its application range.