Giant Piezoelectric Properties And Mechanism Of Lead Nickelniobate-Lead Zirconate Titanate Based Ceramics

Pb(Ni_1/3Nb_2/3)O₃-Pb Zr O₃-Pb Ti O₃（PNN-PZT）ceramics have attracted much attention in recent years due to their excellent piezoelectric properties.The piezoelectric coefficient d₃₃（>1000 p C/N）of PNN-PZT ceramics far exceeds those commonly known soft piezoceramics,but the mechanism of giant piezoelectricity in PNN-PZT ceramics is still not fully understood.In addition,in all kinds of soft piezoelectric ceramics including PNN-PZT,how to achieve both high piezoelectric performance and temperature stability is the current research focus.Soft piezoelectric ceramics also tend to have a high dielectric loss and a small mechanical quality factor,which makes them unstable when driven by continuous electrical signals.Therefore,how to make soft ceramics have low dielectric loss and low mechanical loss while maintaining their high piezoelectric properties is still a challenge up to date.In view of the above mentioned problems,the main research contents of this thesis are as follows:First,the mechanism of giant piezoelectric properties of PNN-PZT ceramics was investigated.PNN-PZT ceramics with different compositions were prepared by solid-state sintering method.PNN-PZT ceramics with the piezoelectric coefficient d₃₃ up to1200 p C/N were prepared by optimizing the sintering process.The results of dielectric temperature spectrum,XRD and domain structure morphology show that the ultrahigh piezoelectric properties of PNN-PZT ceramics are due to the coexistence of rhombohedral phase,tetragonal phase and pseudo-cubic phase.There are more self-polarized orientations in the ceramics,which makes it easier to change the domain structure,and thus the dielectric and piezoelectric properties become better.Then the piezoelectric properties of PNN-PZT were further improved by texture technology.<001>oriented PNN-PZT textured ceramics with different template content were prepared by TGG method using barium titanate seed crystal as template.The results show that for PNN-PZT ceramics with high dielectric constant,the piezoelectric properties of textured ceramics first increase and then decrease with the increase of template content.The improvement of piezoelectric properties is due to the grain orientation growing along<001>direction,which reduces the domain size.The decrease of piezoelectric properties of ceramics is due to the sharp decrease of the dielectric constant of ceramics.Then the temperature stability of ceramics was improved by texture technology.PNN-PZT at MPB region was selected for texturing,and the phase transition temperature was dispersed through the clamping effect brought by the template,so as to improve the temperature stability.After texture treatment,the piezoelectric and electromechanical properties of the ceramics are improved,and the temperature stability is greatly improved.The effective piezoelectric coefficient d^*₃₃ of 3BT texture ceramics varies only 4.9%from 20℃to 150℃,which is much lower than that of ordinary ceramics 46.7%.Finally,the problem of high mechanical and dielectric loss of PNN-PZT ceramics was optimized.Pb(Mn_1/3Nb_2/3)O₃ was introduced to replace Pb(Ni_1/3Nb_2/3)O₃ by manganese doping method,and defective dipole was artificially introduced to pin spontaneous dipole.The results show that the composite properties of0.02Pb(Mn_1/3Nb_2/3)O₃-0.53Pb(Ni_1/3Nb_2/3)O₃-0.135Pb Zr O₃-0.315Pb Ti O₃ ceramics are better,and the dielectric loss is only 0.45%when the piezoelectric constant is 760 p C/N.At the same time,the mechanical quality factor is 247,achieving the coexistence of high piezoelectric constant and low dielectric loss.Compared with the commercial PZT-5H energy collector,the output power and output current of the energy collector prepared with PMn N-PNN-PZT ceramic are 85%higher and 52%higher than those of commercial PZT-5H energy collector.