Research On The Electrical Properties And Energy Storage Density Of Highly Transparent KNN-MZN (M=Ca, Sr, Bi) Ceramics

Transparent ferroelectric ceramics have bright application prospects in modern optical device technology,future computer technology,electronic information technology and national defense and military because of their decent optical,electrical,mechanical and energy storage properties.Currently,lead-based materials dominate transparent ferroelectric ceramics due to their excellent transparency and electrical properties.Nevertheless,the arising environmental issues limit the widely use of heavy-metal Pb.Researches are thus seeking for lead-free materials with high transparency and decent electrical properties.In this work,to improve optical transparency,electrical properties and energy storage density,we synthesized K0.5Na0.5NbO₃ ceramics with M?Zn,Nb?O₃?M = Ca,Sr,Bi??M = Ca,Sr,Bi?additives using solid-state reaction and pressureless sintering technology.The effects of composition design on the phase structures,microstructures,electrical properties,transparency and energy storage density were then investigated systematically.The main conclusions are as follows:1.By optimizing the ball milling procedures,pre-firing conditions,granulation processes,sintering conditions during the traditional solid method,we successfully prepared?1-x?K0.5Na0.5NbO₃-xCa?Zn1/3Nb2/3?O₃?x = 0.03,0.05,0.06,0.07,0.08,0.10,?1-x?KNN-xCZN?ceramics.The effects of CZN content on phase structure,microstructure,relaxor-like behavior,transparency and electrical properties were investigated.The results showed that with the increase of Ca?Zn1/3Nb2/3?O₃ content,the crystal structure transforms from orthorhombic phase to pseudo-cubic phase,the relaxor-like behavior becomes more obvious,the grain size first decreases and then increases,and the optical transmittance first increases and then decreases.The ceramics,as x = 0.07,possess pseudo-cubic phase structure,fine-grain size?the main size is 195 nm?,dense microstructure?the relative density is 98%?,and more obvious relaxor-like behavior.Besides,the high transmittance of over 80%in the near-infrared region and over 70%in the visible region and the excellent electrical properties of the x = 0.07 ceramics were achieved,i.e.,?s = 1162,d33 = 102pC/N.2.?1-x?K0.5Na0.5NbO₃-xSr?Zn1/3Nb2/3?O₃?x = 0.03,0.05,0.06,0.07,0.08,0.10,?1-x?KNN-xSZN?ceramics were successfully designed and prepared.The effects of SZN content on phase structure,grain size,relaxor-like structure,transparency and energy storage density were investigated.The results showed that the ceramics with pure perovskite structure,dense and fine-grained microstructure,relaxor-like behavior were synthesized.With the increase of Sr?Zn1/3Nb2/3?O₃ content,the crystal structure transforms from orthorhombic phase to pseudo-cubic phase,the grain size first decreases and then increases and the relaxor-like behavior becomes more obvious.The ceramics with x = 0.06 possess pseudo-cubic phase structure,smallest grain size,highest density,maximum optical transmittance and highest energy storage density,i.e.,T = 80%at 1064 nm and T = 73%at 780 nm,Wtotal = 3.0 J/cm³,Wrec= 1.5 J/cm³?under an electric field of 180 kV/cm?.In addition,compared with?1-x?KNN-xCZN ceramics,?1-x?KNN-xSZN ceramics possess smaller grains,more obvious relaxor-like behavior and lower concentration of SZN for phase transition and grain minimization,so more excellent transparency and energy storage density.3.?1-x?K0.5Na0.5NbO₃-xBi?Zn2/3Nb1/3?O₃?x = 0.03,0.05,0.06,0.07,0.08,?1-x?KNN-xBZN?ceramics were successfully designed and prepared.The effects of BZN content on phase structure,grain size,relaxor-like behavior,transparency,energy storage density and electrical properties were investigated.The results showed that the pure perovskite structure and low symmetric orthorhombic phase were maintained,the grain growth was inhibited,and the transmittance,electrical properties and energy storage density were enhanced.Increasing the BZN concentration resulted in an increased grain size so the decreased transmittance in the visible region.The diffusion factor ? of the ceramics was increased with increasing BZN concentration,showing the maximum value 1.90 at x = 0.08,which indicates that the ceramics are transformed from normal ferroelectrics to relaxor ferroelectrics.As a result,the light scattering of ceramics is much lower than that of macrodomains in normal ferroelectrics,thus increasing the transmittance of ceramics,especially in the near-infrared region.In summary,the novel near-infrared transparency,i.e.,T = 91%about 2000 nm,was achieved in low-symmetry orthorhombic?1-x?K0.5Na0.5NbO₃-xBi?Zn2/3Nb1/3?O₃?KNN-xBZN?ceramics,as x = 0.06.Meanwhile,the low symmetry of orthorhombic phase structure assured decent electrical properties and energy storage density in the ceramics,i.e.,?m = 1337,Pr = 5.28 ?C/cm2,Wtotal =1.4 J/cm³,Wrec = 0.7 J/cm³ as x = 0.06.