Preparation And Performance Study Of Potassium Sodium Niobate-based Dielectric Energy Storage Ceramic

With the rapid growth of global energy demand,a major challenge facing humanity is how to develop sustainable and renewable energy,making the acquisition,conversion,and storage of renewable energy particularly urgent.Energy storage ceramic capacitors have good stability and can meet the needs of the new era in new energy,so they are widely used in different fields.Developing energy storage ceramic systems with high energy density and good temperature stability has become particularly crucial.Potassium sodium niobate ceramics have excellent ferroelectric properties and are environmentally friendly,making them a promising alternative to lead-based energy storage ceramic materials.Therefore,this study adopts potassium sodium niobate（KNN）as the matrix,inducing the appearance of polar nanoregions through non-equivalent ion doping to improve the energy storage performance of ceramics.The main research content is as follows:1.A novel lead-free ceramic（1-x）K_0.5Na_0.5NbO₃-xBi Mg_0.5Sn_0.5O₃（x=0.06,0.08,0.1,0.12）was prepared by a solid-state method.When x≤0.1,BMS diffused completely into the KNN lattice,forming a solid solution with a perovskite structure.When x=0.12,a second phase appeared in the ceramic,transforming the ferroelectric rhombohedral（R）phase to the paraelectric cubic（C）phase.The grain size of the ceramic significantly decreased,and when x=0.1,it decreased to 235.53 nm.In addition,the introduction of Bi³⁺and(Mg_0.5Sn_0.5)³⁺caused frequency dispersion in the dielectric curve of the ceramic,increasing its relaxation degree.The 0.94K_0.5Na_0.5NbO₃-0.06Bi Mg_0.5Sn_0.5O₃ceramic achieved the maximum total energy storage density W_tot=2 J/cm³ and recoverable energy storage density W_rec=0.89 J/cm³under an electric field of 150 k V/cm.The 0.9K_0.5Na_0.5NbO₃-0.1Bi Mg_0.5Sn_0.5O₃ ceramic achieved the highest energy storage efficiencyη=70.5%.2.A new lead-free ceramic（1-x）K_0.5Na_0.5NbO₃-xBi_0.5La_0.5Zn_0.5Sn_0.5O₃（x=0.08,0.1,0.12,0.14）was prepared by solid-state reaction.BLZS is perfectly soluble with KNN,and as the amount of BLZS increases,the phase structure of the ceramic gradually changes from tetragonal（T）phase to cubic（C）phase.The addition of BLSZ reduced the grain size of the ceramic,and when x=0.12,the grain size of the ceramic was 280μm.The addition of BLZS improved the relaxation performance of the ceramic,and the ceramic with a composition of 0.88K_0.5Na_0.5NbO₃-0.12Bi_0.5La_0.5Zn_0.5Sn_0.5O₃obtained the maximumΔT_m,and the dispersity factor was closer to 2 with a value of1.84.The ceramic with a composition of 0.86K_0.5Na_0.5NbO₃-0.14Bi_0.5La_0.5Zn_0.5Sn_0.5O₃obtained the maximum total energy storage density W_tot=1.1 J/cm³ and recoverable energy storage density W_rec=0.84 J/cm³ at an electric field of around 180 k V/cm,while the ceramic with a composition of 0.92K_0.5Na_0.5NbO₃-0.08Bi_0.5La_0.5Zn_0.5Sn_0.5O₃obtained the maximum energy storage efficiencyη=87%.3.A new lead-free ceramic（1-x）K_0.5Na_0.5NbO₃-xBa_0.5Sr_0.5(Zn_1/3Nb_2/3)O₃（x=0.06,0.08,0.1,0.12）was prepared by solid-state method.According to the XRD pattern,there was no significant shift in the diffraction peaks,and the ceramic transformed from ferroelectric rhombohedral（R）phase to paraelectric cubic（C）phase.The density of the ceramic was improved relative to pure KNN ceramic,and the maximum density was4.6089 g/cm³ when x=0.06.The ceramic exhibited good frequency stability,and the phase transition temperature gradually shifted towards room temperature.The ceramic0.92K_0.5Na_0.5NbO₃-0.08Ba_0.5Sr_0.5(Zn_1/3Nb_2/3)O₃ had the largest△T_m and showed strong relaxation behavior.The addition of BSZN reduced both the maximum polarization P_max and the residual polarization P_r,which first decreased and then increased.When x=0.06,the ceramic obtained the maximum saturation polarization P_max=18.16μc/cm².The ceramic 0.94K_0.5Na_0.5NbO₃-0.06Ba_0.5Sr_0.5(Zn_1/3Nb_2/3)O₃achieved the highest total energy storage density W_tot=1.77 J/cm³ at around 150 k V/cm,while the ceramic 0.92K_0.5Na_0.5NbO₃-0.08Ba_0.5Sr_0.5(Zn_1/3Nb_2/3)O₃ had the maximum recoverable energy storage density W_rec=0.8 J/cm³ and energy storage efficiencyη=58.8%.4.A new lead-free ceramic,0.85K_0.5Na_0.5NbO₃-0.15Bi Zn_0.5Ti_0.5O₃-xMn,was prepared by solid-state reaction.Compared with pure KNN ceramics,the a and b（a=b）values of KNN-BZT and KNN-BZT-Mn ceramics increased,while c decreased,indicating negative stress imposed by BZT and Mn O₂ on the lattice,which resulted in the transformation of the relaxor ferroelectric rhombic（R）phase to the paraelectric cubic（C）phase.The doping of BZT and Mn O₂caused the ceramics to exhibit diffuse phase transition-like relaxor properties in their dielectric performance,and the hysteresis loops of the ceramics became refined.The 0.85K_0.5Na_0.5NbO₃-0.15Bi Zn_0.5Ti_0.5O₃ ceramic obtained a high recoverable energy density W_rec=0.7116J/cm³ and energy storage efficiencyη=78.77%at an electric field of about 150 k V/cm,whereas in the 0.85K_0.5Na_0.5NbO₃-0.15Bi Zn_0.5Ti_0.5O₃-Mn ceramic,the maximum recoverable energy density W_rec=1.0933 J/cm³ and energy storage efficiencyη=78.92%were achieved.