Study On The Structure Of Silver Niobate Based Composites And Their Energy Storage Performance

With the rapid development of pulsed power technology,dielectric capacitors have attracted much attention due to their high power density and fast charge/discharge rates.Although lead-based antiferroelectric ceramics have good energy storage performance,there is a continuous need to explore environmentally friendly lead-free energy storage materials due to their environmental toxicity.Silver niobate（AN）with large saturation polarization strength（P）has potential applications in the field of pulsed power high density energy storage materials.However,AN materials have a strong ferroelectric state at room temperature,which limits their energy storage density and low energy storage efficiency.Therefore,the focus of this thesis is to adjust the composition of AN ceramic components,refine the electric hysteresis（P-E）and enhance the antiferroelectric behavior of AN to improve the recoverable energy storage density（Wrec）and energy storage efficiency（η）of AN.Firstly,the introduction of Bi³⁺（smaller ionic radius）at the A-site and Ta⁵⁺（smaller ionic polarization rate）embedded at the B-site were considered to reduce the material tolerance factor and jointly improve the sample antiferroelectricity and thus refine the P-E return line;the significantly improved antiferroelectric properties were confirmed by microscopic morphology,physical structure and electrical property analysis,and the modified AN-based ceramics showed a certain degree of increase in breakdown voltage Eb,which was achieved in The excellent recoverable energy storage density Wrec～3.9 J/cm³ and η of 61%were achieved in the BANT6 component,which is a significant improvement compared to the pure silver niobate matrix（Wrec～1.8 J/cm³）.It shows that Bi/Ta co-doped silver niobate has some prospects for energy storage applications.To further explore the effect of grain size on the energy storage performance of AN ceramics,HfO₂ with higher melting point was introduced to effectively reduce the average grain size of the ceramics;the introduction of Hf⁴⁺ at the B-position caused defective dipoles in the samples,limiting the movement of oxygen vacancies thus making the material long-range disordered and effectively improving the antiferroelectric properties of the samples;to ensure the electrovalent balance,Ca²⁺ at the A-position was chosen to replace Ag⁺.To ensure the electrovalence balance,Ca²⁺at the A-site was chosen to replace Ag⁺to form AN-CaHfO₃ ceramic solid solution with silver niobate.The physical phase analysis confirmed the successful solid solution of CaHfO₃ into AN ceramics;the morphological analysis showed that the introduction of CaHfO₃ significantly reduced the grain size of AN ceramics,resulting in the improvement of the denseness of the samples;the electrical properties of the samples with different doping contents were quantified and the optimal properties were obtained:at the doping content x of 0.02 mol%,the AN-CaHfO₃ ceramics obtained excellent energy.The comprehensive analysis of the performance indicates that the reduction of grain size is beneficial to improve the voltage tolerance of the samples and limitedly improve the energy storage performance of the material.Based on the above grain size reduction strategy,in order to further improve the breakdown field strength Eb and continuously improve the antiferroelectricity of the sample,a higher melting point rare earth oxide Gd₂O₃ is introduced into AN to induce densification and grain refinement of the material;in addition,as demonstrated above,the heterovalent ion doping tends to promote the generation of cation vacancies in the sample,which is favorable to the emergence of disordered behavior in the material;applying the above design scheme to the The above design scheme was applied to the Ag(Nb_0.85Ta_0.15)O₃ ceramics formed by the optimal energy storage scheme Ta⁵⁺doping,and the Gd³⁺doping content was attempted to be varied,and it was observed by morphological analysis that the grain size of AN-based ceramics continued to decrease with the increase of Gd³⁺doping,and the denseness of the samples increased;there was no typical second-phase diffraction peak in the physical phase structure,which proved that Gd³⁺solid solution into the AN matrix formed The dielectric properties study revealed that the doping significantly changed the phase transition behavior of the material,as well as the obvious chirality behavior,which matched the gradually elongated antiferroelectric P-E return line of the sample,and the GATN2 ceramic obtained a higher effective energy storage density W_rec～4.99 J/cm³ at 360 kV/cm at x equal to 0.02 mol%,while maintaining a high energy storage efficiency η～68%.