Structural And Electrical Properties Of Sodium Potassium Niobate-Based Binary System Ceramics

Piezoelectric materials are functional materials that enable the interconversion of mechanical and electrical energy and are widely used in electronics,machinery and other fields.Lead zirconate titanate based ceramics have always occupied an important position in the market of piezoelectric materials due to their superior dielectric and pi-ezoelectric properties.However,lead-based ceramics contain large amounts of lead,which not only endangers human health,but also causes serious damage to the environ-ment.Therefore,in order to maintain a sustainable society,the search for a green and environmentally friendly lead-free piezoelectric system has become an important task in materials science research.Lead-free piezoelectric ceramics based on potassium so-dium niobate（KNN）stand out among the many environmentally friendly ceramic ma-terials due to their excellent piezoelectric properties.Currently,KNN-based ceramic materials have become a major research hotspot in the field of piezoelectric ceramics.However,compared to lead-based ceramics,KNN-based ceramics have lower piezoe-lectric properties and can hardly act as a replacement for lead-based ceramics.In order to meet the practical needs,KNN-based ceramics need to be optimised.Studies have shown that the construction of polycrystalline phase boundaries in KNN-based ceram-ics by means of doping modifications can effectively enhance the electrical properties.In this regard,the construction of phase boundaries has become a mainstream research direction in the development of KNN-based ceramics.Therefore,in this paper,three ceramic systems with excellent overall properties were designed by introducing suitable second group elements for component optimiza-tion and phase boundary construction of KNN ceramics,as follows:（1）The（1-x）K_0.48Na_0.52NbO₃-xBa_0.05(Bi_0.5K_0.5)_0.95ZrO₃（0≤x≤0.05）（abbreviated as KNN-x BBKZ）ceramic materials were prepared by the conventional solid-state method.The effects of BBKZ doping on the structural and electrical properties of KNN ceramics were investigated and characterised by studying the crystal structure,micro-scopic morphology,dielectric properties and piezoelectric properties.All ceramic sam-ples were found to be pure perovskite phase by XRD,SEM and EDS,and all BBKZ ions entered the KNN lattice to form a stable solid solution,with the increase of doping,the ceramic grains become morecompact and dense,but too much doping will hinder the grain growth and make the ceramic grain size drop rapidly,leading to more domain walls,which makes the electrical properties degrade.The analysis of the ceramics’ε_r-T curves shows that with increasing doping,the ceramic evolves from a single orthog-onal phase to a coexistence of orthogonal-tetragonal phases.The best electrical proper-ties are obtained at x=0.04(d₃₃=269 p C/N,k_p=41%,ε_r=1423,tanδ=2.8%,P_r=17.57μC/cm²,E_c=14.67 k V/cm,T_C=343℃),while the Curie temperature remains at a high level.（2）The（1-x）K_0.48Na_0.52NbO₃-xBa_0.05(Bi_0.5K_0.5)_0.95Zr_0.9Ti_0.1O₃（0≤x≤0.05）（abbre-viated as KNN-x BBKZT）ceramic materials were prepared by the conventional solid-state method.The results of microscopic morphology,crystal structure and electrical properties show that BBKZT completely enters into the KNN lattice and forms a pure perovskite phase,and the ceramic phase structure appears to change from O phase to O-T phase and then to R-T phase structure with the increase of doping.As the multi-phase coexistence promotes the domain wall motion and polarization rotation of the ceramics,thus improving the electrical properties of the ceramics.The best ceramic properties were obtained at x=0.04(d₃₃=288 p C/N,k_p=42.68%,ε_r=1443,tanδ=1.72%,P_r=17.76μC/cm²,E_c=16.9 k V/cm,and T_C=348℃),and the Curie tempera-ture remained at a high level while the piezoelectric properties were further improved.（3）（1-x）(K_0.5Na_0.5)NbO₃-x(Bi_0.5K_0.5)_0.92Zn_0.08ZrO₃（0≤x≤0.06）（abbreviated as KNN-x BKZZ）was prepared by the conventional solid-state method.The effects of BKZZ on the microstructure,phase structure,dielectric properties and piezoelectric properties of KNN ceramics were systematically investigated.The XRD and EDS test results showed that all ions of BKZZ entered into the KNN lattice and formed a pure perovskite phase.The ceramics’ε_r-T curves test results show that at the doping amount of 0.05≤x≤0.06,the R-T phase boundary is successfully constructed,which promotes the rotation of electric domains during the polarization process,thus enabling the elec-trical properties of the ceramics to be enhanced.The best properties was exhibited at x=0.05(d₃₃=330 p C/N,k_p=49%,ε_r=1374,tanδ=2.4%,P_r=20.6μC/cm²,E_c=18.55k V/cm,and T_C=345℃),with a large improvement of the piezoelectric properties while the Curie temperature did not decrease.At the same time,the addition of the appropriate amount of BKZZ increases the density of the ceramic,which has a positive effect on the electrical properties of the ceramic.