Phase Boundary Construction And Property Optimization Of Zirconate-doped Modified KNN-based Piezoelectric Ceramics

Piezoelectric ceramics are ceramic materials that convert mechanical and electrical energy to each other through the piezoelectric effect,and have been widely used in information sensing,aerospace,in the military and in daily life.The reason why piezoelectric ceramics are widely used,among which,lead-based ceramics represented by the binary system lead zirconate titanate(PZT)are widely used in communications,resonators and PZT ceramics are widely used in communication,resonator and sensor fields,especially in aerospace applications.However,PZT ceramics have caused serious damage to the earth’s environment and human health due to lead elements in manufacturing and use.Therefore,the search for a piezoelectric ceramic that can replace PZT ceramics and is environmentally friendly and non-toxic has become a hot topic of current research.Among the piezoelectric materials,K0.5Na0.5NbO3(KNN)based ceramics are the most likely to replace Pb-based materials due to their excellent piezoelectricity and high Curie temperature,but KNN-based piezoelectric ceramics have problems such as easy volatility of alkali metal elements,poor densification,and difficulty in balancing piezoelectricity and Curie temperature.Based on the above research background,this thesis mainly focuses on KNNbased piezoelectric ceramics as the research object regarding the components and physical properties,choosing zirconate as the main dopant of the second group element and introducing suitable ionic doping for KNN-based ceramics substitution doping.The specific research contents and results are as follows:(1)K0.45Na0.55NbO3 was used as the matrix,and the second group element(Bi0.5Li0.5)0.9Sr0.1ZrO3(abbreviated as BLSZ)was introduced to successfully prepare(1-x)KNN-xBLSZ ceramics by the conventional solid-phase synthesis method,and the crystal phase structure,ceramic microstructure,dielectric properties,piezoelectric properties,and ferroelectric properties were the effects of BLSZ-doped KNN ceramics were analyzed in depth.The XRD and EDS tests can confirm that the doping of BLSZ completely forms a pure solid solution chalcogenide structure,and all the elements enter into the KNN lattice.With the increase of the doping amount,the phase structure of the ceramics gradually changes from orthogonal single phase to orthogonal-quadratic coexistence phase,and when the doping amount content is 0.04,a tripartite-quadratic phase is constructed,and at this time the ceramics exhibit the enhancement of electrical properties:d33=307pC/N,kp=46%,while the ceramic maintains an excellent Curie temperature of TC=368℃,which allows the current ceramic to maintain high piezoelectric properties without lowering the Curie temperature,in addition,the improved performance of the ceramic partly comes from the improvement of the denseness,ceramic grains show a uniform distribution phenomenon.In summary,the introduction of the second element of BLSZ is beneficial to the construction of new phase boundaries at room temperature,the maintenance of high Curie temperature and the improvement of ceramic densities.(2)Firstly,we chose to introduce Ag+and Ta5+ doping substitution in the A and B positions of KNN-based ceramics,respectively,and prepared the matrix K0.44Na0.55Ag0.01Nb0.95Ta0.05O3,and introduced the second component(Bi0.5Li0.5)0.9Sr0.1ZrO3(abbreviated as BLSZ),and successfully prepared the(1x)KNANT-xBLSZ ceramics were successfully prepared using the conventional solidphase synthesis method,and the ceramic crystal structure,microscopic morphology,piezoelectric properties,relaxation properties and ferroelectric properties were analyzed and studied in terms of the BLSZ components as variables.By the comprehensive analysis of XRD patterns and dielectric temperature spectra,the phase structure of the ceramics gradually changes from orthogonal to orthogonal-quadratic phase when 0≤x≤0.035,and the phase structure of the ceramics is tripartite-quadratic at room temperature when 0.035≤x≤0.06.The electrical properties of the ceramics are best at x=0.035:d33=312pC/N,kp=46.5%,based on the good electrical properties of the matrix,the doping of BLSZ makes the Curie temperature change very little,enhancing the electrical properties while still maintaining a high Curie temperature of TC=342℃.In addition,the overall grain distribution of the ceramics is uniform,but excessive doping will make the inhibition of The grain growth is inhibited by excessive doping,which leads to an increase in the density of domain walls inside the ceramic,resulting in a decrease in the overall performance.The dispersive phase transition in the ceramics can also be stabilized to some extent by doping with appropriate amount of BLSZ,but too much doping will still cause lattice distortion and inhomogeneous composition of the ceramics,making the dispersion more serious.(3)In order to construct the new phase boundary more effectively,the matrix K0.45Na0.55Nb0.965Sb0.035O3 was prepared by introducing Sb5+into the KNN-based ceramics,while the second group element(0.9Bi0.5Li0.5ZrO3-0.1 SrSnO3)(referred to as BLZ-SS)was introduced for composite doping,and the conventional solid-phase synthesis was used to(1-x)KNNS-x(BLZ-SS)ceramics were prepared and discussed by comprehensive analysis of X-ray diffraction analysis,microstructure,dielectric temperature spectrum,energy spectrum analysis and ferroelectric properties.Firstly,it can be found that all ceramics form a pure chalcogenide structure,and the combination of EDS confirms that the elements are uniformly distributed in the ceramics.Secondly,the comprehensive XRD and dielectric temperature spectroscopy results show that the doping of BLZ-SS,when x=0.035,constructs a new R-T multiphase coexistence phase boundary at room temperature,when the internal region of the ceramics has more polarizable states,and the electric domains become more easily flipped,exhibiting The enhanced electrical properties:d33=324pC/N,kp=49%,were not maintained to the higher Curie temperature TC=293℃ by doping and group element introduction although the piezoelectric properties were improved.in addition,the doping of moderate amount of BLZ-SS made the overall distribution of grains uniform and showed good densities,and when the doping amount gradually increased,the ceramics showed diffuse phase transition phenomenon,which led to the appearance of When the amount of doping gradually increases,the ceramic has a dispersive phase transition,resulting in a lower density of ceramic,which also becomes one of the reasons for the decline in ceramic performance.Comprehensive analysis of doping BLZ-SS can effectively build poly crystalline phase boundary,so that the performance is improved,but the impact on the Curie temperature is more obvious,which has a certain impact on the temperature range of ceramic applications.At the same time,doping is beneficial to the uniform grain distribution and density of ceramics,which has a positive effect on the electrical properties of ceramics.