Study On Piezoelectric And Flexoelectric And Upconversion Luminescence Properties Of Lead-Free Piezoelectric Ceramics

Piezoelectric ceramics have a wide range of applications in sensors and transducers,but the most widely used piezoelectric ceramics are Pb?Zr,Ti?O₃ based ceramics at present.Its lead content of up to 60%by mass makes Pb?Zr,Ti?O₃ ceramics take great pressure on the environment during the preparation and recycling process,which is the reason for developing fungible lead-free piezoelectric ceramics urgently.The lead-free piezoelectric ceramics,?K,Na?NbO₃ and BaTiO₃,have attractived many researcher'interest,Pb?Zr,Ti?O₃ is most likely to be replaced by these materials.However,the piezoelectric coefficient of pure?K,Na?NbO₃ ceramic is weak,and its the piezoelectric properties needs to be modified by doping various elements.In addition,as a new force-electric coupling effect,flexoelectric effect broadens the application of electromechanical coupling,but there is still no report about the flexoelectric property of?K,Na?NbO₃ ceramics.The upconversion photoluminescence of rare-earth ions has been noticed long before,but the upconversion luminescence properties of rare-earth doped piezoelectric ceramics is not ideal.Therefore,in this paper,we studied the piezoelectric and flexoelectric properties of?K,Na?NbO₃-based ceramics and the enhanced method of the upconversion photoluminescence for rare-earth doped BaTiO₃-based ceramics.1.?1-x?K_0.4Na_0.58Li_0.02Nb_0.96Sb_0.04O₃-xBi_0.5Na_0.5ZrO₃ lead-free piezoelectric ceramics have been prepared by the conventional solid-state method.Doping Bi_0.5Na_0.5ZrO₃ shifts the phase transition temperature of ceramics near to room temperature,the phase structure of ceramics changed from Orthorhombic phase?O?to Orthorhombic-Tetragonal phase?O-T?and Tetragonal-Rhombohedral phase?R-T?,at room temperature.The component at the R-T polymorphic phase boundary has a maximum piezoelectric coefficient d₃₃=282 pC/N,the dielectric constant of the component is 1029,and T_C is 287°C.2.Flexoelectric propertie of K_0.4Na_0.58Li_0.02Nb_0.96Sb_0.04O₃ ceramics have been measured.The flexoelectric coefficient is as high as 1-2?C/m,which is much larger than the theoretical eigenvalue of the flexoelectric coefficient for most materials.And the fatigue effect of the flexoelectric have been studied,In the long-term periodic vibration measurement,the ceramic's flexoelectric coefficient decreased by about 30%and then stabilized.A stretched exponential function fits the fatigue behavior of the flexoelectric coefficient very well.The fatigue phenomenon of the flexoelectric should be derived from the diffusion of oxygen vacancies.3.The doped of In³⁺ions greatly enhances the upconversion photoluminescence of Ba_0.85Ca_0.15TiO₃:0.75%Er³⁺lead-free piezoelectric ceramics.Exicted by 980 nm laser,the upconversion emission intensity reaches the maximum at x=1.75 mol%for In³⁺ions doped,where the emission intensity is unprecedentedly?²000%?larger than that of the In³⁺ions undoped ones.Analysis of UV-VIS-NIR absorption spectra reveal that the In³⁺ions doping changes the Er³⁺ions distribution,thereby favoring the excited state absorption process and reducing cross relaxation?CR?process.